"""
A module for converting numbers or color arguments to *RGB* or *RGBA*.
*RGB* and *RGBA* are sequences of, respectively, 3 or 4 floats in the
range 0-1.
This module includes functions and classes for color specification conversions,
and for mapping numbers to colors in a 1-D array of colors called a colormap.
Mapping data onto colors using a colormap typically involves two steps: a data
array is first mapped onto the range 0-1 using a subclass of `Normalize`,
then this number is mapped to a color using a subclass of `Colormap`. Two
subclasses of `Colormap` provided here: `LinearSegmentedColormap`, which uses
piecewise-linear interpolation to define colormaps, and `ListedColormap`, which
makes a colormap from a list of colors.
.. seealso::
:doc:`/tutorials/colors/colormap-manipulation` for examples of how to
make colormaps and
:doc:`/tutorials/colors/colormaps` for a list of built-in colormaps.
:doc:`/tutorials/colors/colormapnorms` for more details about data
normalization
More colormaps are available at palettable_.
The module also provides functions for checking whether an object can be
interpreted as a color (`is_color_like`), for converting such an object
to an RGBA tuple (`to_rgba`) or to an HTML-like hex string in the
"#rrggbb" format (`to_hex`), and a sequence of colors to an (n, 4)
RGBA array (`to_rgba_array`). Caching is used for efficiency.
Matplotlib recognizes the following formats to specify a color:
* an RGB or RGBA (red, green, blue, alpha) tuple of float values in closed
interval ``[0, 1]`` (e.g., ``(0.1, 0.2, 0.5)`` or ``(0.1, 0.2, 0.5, 0.3)``);
* a hex RGB or RGBA string (e.g., ``'#0f0f0f'`` or ``'#0f0f0f80'``;
case-insensitive);
* a shorthand hex RGB or RGBA string, equivalent to the hex RGB or RGBA
string obtained by duplicating each character, (e.g., ``'#abc'``, equivalent
to ``'#aabbcc'``, or ``'#abcd'``, equivalent to ``'#aabbccdd'``;
case-insensitive);
* a string representation of a float value in ``[0, 1]`` inclusive for gray
level (e.g., ``'0.5'``);
* one of the characters ``{'b', 'g', 'r', 'c', 'm', 'y', 'k', 'w'}``, which
are short-hand notations for shades of blue, green, red, cyan, magenta,
yellow, black, and white. Note that the colors ``'g', 'c', 'm', 'y'`` do not
coincide with the X11/CSS4 colors. Their particular shades were chosen for
better visibility of colored lines against typical backgrounds.
* a X11/CSS4 color name (case-insensitive);
* a name from the `xkcd color survey`_, prefixed with ``'xkcd:'`` (e.g.,
``'xkcd:sky blue'``; case insensitive);
* one of the Tableau Colors from the 'T10' categorical palette (the default
color cycle): ``{'tab:blue', 'tab:orange', 'tab:green', 'tab:red',
'tab:purple', 'tab:brown', 'tab:pink', 'tab:gray', 'tab:olive', 'tab:cyan'}``
(case-insensitive);
* a "CN" color spec, i.e. 'C' followed by a number, which is an index into the
default property cycle (:rc:`axes.prop_cycle`); the indexing is intended to
occur at rendering time, and defaults to black if the cycle does not include
color.
.. _palettable: https://jiffyclub.github.io/palettable/
.. _xkcd color survey: https://xkcd.com/color/rgb/
"""
import base64
from collections.abc import Sized, Sequence
import copy
import functools
import inspect
import io
import itertools
from numbers import Number
import re
from PIL import Image
from PIL.PngImagePlugin import PngInfo
import matplotlib as mpl
import numpy as np
from matplotlib import _api, cbook, scale
from ._color_data import BASE_COLORS, TABLEAU_COLORS, CSS4_COLORS, XKCD_COLORS
class _ColorMapping(dict):
def __init__(self, mapping):
super().__init__(mapping)
self.cache = {}
def __setitem__(self, key, value):
super().__setitem__(key, value)
self.cache.clear()
def __delitem__(self, key):
super().__delitem__(key)
self.cache.clear()
_colors_full_map = {}
# Set by reverse priority order.
_colors_full_map.update(XKCD_COLORS)
_colors_full_map.update({k.replace('grey', 'gray'): v
for k, v in XKCD_COLORS.items()
if 'grey' in k})
_colors_full_map.update(CSS4_COLORS)
_colors_full_map.update(TABLEAU_COLORS)
_colors_full_map.update({k.replace('gray', 'grey'): v
for k, v in TABLEAU_COLORS.items()
if 'gray' in k})
_colors_full_map.update(BASE_COLORS)
_colors_full_map = _ColorMapping(_colors_full_map)
_REPR_PNG_SIZE = (512, 64)
[docs]def get_named_colors_mapping():
"""Return the global mapping of names to named colors."""
return _colors_full_map
def _sanitize_extrema(ex):
if ex is None:
return ex
try:
ret = ex.item()
except AttributeError:
ret = float(ex)
return ret
def _is_nth_color(c):
"""Return whether *c* can be interpreted as an item in the color cycle."""
return isinstance(c, str) and re.match(r"\AC[0-9]+\Z", c)
[docs]def is_color_like(c):
"""Return whether *c* can be interpreted as an RGB(A) color."""
# Special-case nth color syntax because it cannot be parsed during setup.
if _is_nth_color(c):
return True
try:
to_rgba(c)
except ValueError:
return False
else:
return True
def _check_color_like(**kwargs):
"""
For each *key, value* pair in *kwargs*, check that *value* is color-like.
"""
for k, v in kwargs.items():
if not is_color_like(v):
raise ValueError(f"{v!r} is not a valid value for {k}")
[docs]def same_color(c1, c2):
"""
Return whether the colors *c1* and *c2* are the same.
*c1*, *c2* can be single colors or lists/arrays of colors.
"""
c1 = to_rgba_array(c1)
c2 = to_rgba_array(c2)
n1 = max(c1.shape[0], 1) # 'none' results in shape (0, 4), but is 1-elem
n2 = max(c2.shape[0], 1) # 'none' results in shape (0, 4), but is 1-elem
if n1 != n2:
raise ValueError('Different number of elements passed.')
# The following shape test is needed to correctly handle comparisons with
# 'none', which results in a shape (0, 4) array and thus cannot be tested
# via value comparison.
return c1.shape == c2.shape and (c1 == c2).all()
[docs]def to_rgba(c, alpha=None):
"""
Convert *c* to an RGBA color.
Parameters
----------
c : Matplotlib color or ``np.ma.masked``
alpha : float, optional
If *alpha* is not ``None``, it forces the alpha value, except if *c* is
``"none"`` (case-insensitive), which always maps to ``(0, 0, 0, 0)``.
Returns
-------
tuple
Tuple of ``(r, g, b, a)`` scalars.
"""
# Special-case nth color syntax because it should not be cached.
if _is_nth_color(c):
from matplotlib import rcParams
prop_cycler = rcParams['axes.prop_cycle']
colors = prop_cycler.by_key().get('color', ['k'])
c = colors[int(c[1:]) % len(colors)]
try:
rgba = _colors_full_map.cache[c, alpha]
except (KeyError, TypeError): # Not in cache, or unhashable.
rgba = None
if rgba is None: # Suppress exception chaining of cache lookup failure.
rgba = _to_rgba_no_colorcycle(c, alpha)
try:
_colors_full_map.cache[c, alpha] = rgba
except TypeError:
pass
return rgba
def _to_rgba_no_colorcycle(c, alpha=None):
"""
Convert *c* to an RGBA color, with no support for color-cycle syntax.
If *alpha* is not ``None``, it forces the alpha value, except if *c* is
``"none"`` (case-insensitive), which always maps to ``(0, 0, 0, 0)``.
"""
orig_c = c
if c is np.ma.masked:
return (0., 0., 0., 0.)
if isinstance(c, str):
if c.lower() == "none":
return (0., 0., 0., 0.)
# Named color.
try:
# This may turn c into a non-string, so we check again below.
c = _colors_full_map[c]
except KeyError:
if len(orig_c) != 1:
try:
c = _colors_full_map[c.lower()]
except KeyError:
pass
if isinstance(c, str):
# hex color in #rrggbb format.
match = re.match(r"\A#[a-fA-F0-9]{6}\Z", c)
if match:
return (tuple(int(n, 16) / 255
for n in [c[1:3], c[3:5], c[5:7]])
+ (alpha if alpha is not None else 1.,))
# hex color in #rgb format, shorthand for #rrggbb.
match = re.match(r"\A#[a-fA-F0-9]{3}\Z", c)
if match:
return (tuple(int(n, 16) / 255
for n in [c[1]*2, c[2]*2, c[3]*2])
+ (alpha if alpha is not None else 1.,))
# hex color with alpha in #rrggbbaa format.
match = re.match(r"\A#[a-fA-F0-9]{8}\Z", c)
if match:
color = [int(n, 16) / 255
for n in [c[1:3], c[3:5], c[5:7], c[7:9]]]
if alpha is not None:
color[-1] = alpha
return tuple(color)
# hex color with alpha in #rgba format, shorthand for #rrggbbaa.
match = re.match(r"\A#[a-fA-F0-9]{4}\Z", c)
if match:
color = [int(n, 16) / 255
for n in [c[1]*2, c[2]*2, c[3]*2, c[4]*2]]
if alpha is not None:
color[-1] = alpha
return tuple(color)
# string gray.
try:
c = float(c)
except ValueError:
pass
else:
if not (0 <= c <= 1):
raise ValueError(
f"Invalid string grayscale value {orig_c!r}. "
f"Value must be within 0-1 range")
return c, c, c, alpha if alpha is not None else 1.
raise ValueError(f"Invalid RGBA argument: {orig_c!r}")
# turn 2-D array into 1-D array
if isinstance(c, np.ndarray):
if c.ndim == 2 and c.shape[0] == 1:
c = c.reshape(-1)
# tuple color.
if not np.iterable(c):
raise ValueError(f"Invalid RGBA argument: {orig_c!r}")
if len(c) not in [3, 4]:
raise ValueError("RGBA sequence should have length 3 or 4")
if not all(isinstance(x, Number) for x in c):
# Checks that don't work: `map(float, ...)`, `np.array(..., float)` and
# `np.array(...).astype(float)` would all convert "0.5" to 0.5.
raise ValueError(f"Invalid RGBA argument: {orig_c!r}")
# Return a tuple to prevent the cached value from being modified.
c = tuple(map(float, c))
if len(c) == 3 and alpha is None:
alpha = 1
if alpha is not None:
c = c[:3] + (alpha,)
if any(elem < 0 or elem > 1 for elem in c):
raise ValueError("RGBA values should be within 0-1 range")
return c
[docs]def to_rgba_array(c, alpha=None):
"""
Convert *c* to a (n, 4) array of RGBA colors.
Parameters
----------
c : Matplotlib color or array of colors
If *c* is a masked array, an ndarray is returned with a (0, 0, 0, 0)
row for each masked value or row in *c*.
alpha : float or sequence of floats, optional
If *alpha* is not ``None``, it forces the alpha value, except if *c* is
``"none"`` (case-insensitive), which always maps to ``(0, 0, 0, 0)``.
If *alpha* is a sequence and *c* is a single color, *c* will be
repeated to match the length of *alpha*.
Returns
-------
array
(n, 4) array of RGBA colors.
"""
# Special-case inputs that are already arrays, for performance. (If the
# array has the wrong kind or shape, raise the error during one-at-a-time
# conversion.)
if np.iterable(alpha):
alpha = np.asarray(alpha).ravel()
if (isinstance(c, np.ndarray) and c.dtype.kind in "if"
and c.ndim == 2 and c.shape[1] in [3, 4]):
mask = c.mask.any(axis=1) if np.ma.is_masked(c) else None
c = np.ma.getdata(c)
if np.iterable(alpha):
if c.shape[0] == 1 and alpha.shape[0] > 1:
c = np.tile(c, (alpha.shape[0], 1))
elif c.shape[0] != alpha.shape[0]:
raise ValueError("The number of colors must match the number"
" of alpha values if there are more than one"
" of each.")
if c.shape[1] == 3:
result = np.column_stack([c, np.zeros(len(c))])
result[:, -1] = alpha if alpha is not None else 1.
elif c.shape[1] == 4:
result = c.copy()
if alpha is not None:
result[:, -1] = alpha
if mask is not None:
result[mask] = 0
if np.any((result < 0) | (result > 1)):
raise ValueError("RGBA values should be within 0-1 range")
return result
# Handle single values.
# Note that this occurs *after* handling inputs that are already arrays, as
# `to_rgba(c, alpha)` (below) is expensive for such inputs, due to the need
# to format the array in the ValueError message(!).
if cbook._str_lower_equal(c, "none"):
return np.zeros((0, 4), float)
try:
if np.iterable(alpha):
return np.array([to_rgba(c, a) for a in alpha], float)
else:
return np.array([to_rgba(c, alpha)], float)
except (ValueError, TypeError):
pass
if isinstance(c, str):
raise ValueError("Using a string of single character colors as "
"a color sequence is not supported. The colors can "
"be passed as an explicit list instead.")
if len(c) == 0:
return np.zeros((0, 4), float)
# Quick path if the whole sequence can be directly converted to a numpy
# array in one shot.
if isinstance(c, Sequence):
lens = {len(cc) if isinstance(cc, (list, tuple)) else -1 for cc in c}
if lens == {3}:
rgba = np.column_stack([c, np.ones(len(c))])
elif lens == {4}:
rgba = np.array(c)
else:
rgba = np.array([to_rgba(cc) for cc in c])
else:
rgba = np.array([to_rgba(cc) for cc in c])
if alpha is not None:
rgba[:, 3] = alpha
return rgba
[docs]def to_rgb(c):
"""Convert *c* to an RGB color, silently dropping the alpha channel."""
return to_rgba(c)[:3]
[docs]def to_hex(c, keep_alpha=False):
"""
Convert *c* to a hex color.
Uses the ``#rrggbb`` format if *keep_alpha* is False (the default),
``#rrggbbaa`` otherwise.
"""
c = to_rgba(c)
if not keep_alpha:
c = c[:3]
return "#" + "".join(format(int(round(val * 255)), "02x") for val in c)
### Backwards-compatible color-conversion API
cnames = CSS4_COLORS
hexColorPattern = re.compile(r"\A#[a-fA-F0-9]{6}\Z")
rgb2hex = to_hex
hex2color = to_rgb
class ColorConverter:
"""
A class only kept for backwards compatibility.
Its functionality is entirely provided by module-level functions.
"""
colors = _colors_full_map
cache = _colors_full_map.cache
to_rgb = staticmethod(to_rgb)
to_rgba = staticmethod(to_rgba)
to_rgba_array = staticmethod(to_rgba_array)
colorConverter = ColorConverter()
### End of backwards-compatible color-conversion API
def _create_lookup_table(N, data, gamma=1.0):
r"""
Create an *N* -element 1D lookup table.
This assumes a mapping :math:`f : [0, 1] \rightarrow [0, 1]`. The returned
data is an array of N values :math:`y = f(x)` where x is sampled from
[0, 1].
By default (*gamma* = 1) x is equidistantly sampled from [0, 1]. The
*gamma* correction factor :math:`\gamma` distorts this equidistant
sampling by :math:`x \rightarrow x^\gamma`.
Parameters
----------
N : int
The number of elements of the created lookup table; at least 1.
data : (M, 3) array-like or callable
Defines the mapping :math:`f`.
If a (M, 3) array-like, the rows define values (x, y0, y1). The x
values must start with x=0, end with x=1, and all x values be in
increasing order.
A value between :math:`x_i` and :math:`x_{i+1}` is mapped to the range
:math:`y^1_{i-1} \ldots y^0_i` by linear interpolation.
For the simple case of a y-continuous mapping, y0 and y1 are identical.
The two values of y are to allow for discontinuous mapping functions.
E.g. a sawtooth with a period of 0.2 and an amplitude of 1 would be::
[(0, 1, 0), (0.2, 1, 0), (0.4, 1, 0), ..., [(1, 1, 0)]
In the special case of ``N == 1``, by convention the returned value
is y0 for x == 1.
If *data* is a callable, it must accept and return numpy arrays::
data(x : ndarray) -> ndarray
and map values between 0 - 1 to 0 - 1.
gamma : float
Gamma correction factor for input distribution x of the mapping.
See also https://en.wikipedia.org/wiki/Gamma_correction.
Returns
-------
array
The lookup table where ``lut[x * (N-1)]`` gives the closest value
for values of x between 0 and 1.
Notes
-----
This function is internally used for `.LinearSegmentedColormap`.
"""
if callable(data):
xind = np.linspace(0, 1, N) ** gamma
lut = np.clip(np.array(data(xind), dtype=float), 0, 1)
return lut
try:
adata = np.array(data)
except Exception as err:
raise TypeError("data must be convertible to an array") from err
shape = adata.shape
if len(shape) != 2 or shape[1] != 3:
raise ValueError("data must be nx3 format")
x = adata[:, 0]
y0 = adata[:, 1]
y1 = adata[:, 2]
if x[0] != 0. or x[-1] != 1.0:
raise ValueError(
"data mapping points must start with x=0 and end with x=1")
if (np.diff(x) < 0).any():
raise ValueError("data mapping points must have x in increasing order")
# begin generation of lookup table
if N == 1:
# convention: use the y = f(x=1) value for a 1-element lookup table
lut = np.array(y0[-1])
else:
x = x * (N - 1)
xind = (N - 1) * np.linspace(0, 1, N) ** gamma
ind = np.searchsorted(x, xind)[1:-1]
distance = (xind[1:-1] - x[ind - 1]) / (x[ind] - x[ind - 1])
lut = np.concatenate([
[y1[0]],
distance * (y0[ind] - y1[ind - 1]) + y1[ind - 1],
[y0[-1]],
])
# ensure that the lut is confined to values between 0 and 1 by clipping it
return np.clip(lut, 0.0, 1.0)
def _warn_if_global_cmap_modified(cmap):
if getattr(cmap, '_global', False):
_api.warn_deprecated(
"3.3",
removal="3.6",
message="You are modifying the state of a globally registered "
"colormap. This has been deprecated since %(since)s and "
"%(removal)s, you will not be able to modify a "
"registered colormap in-place. To remove this warning, "
"you can make a copy of the colormap first. "
f'cmap = mpl.cm.get_cmap("{cmap.name}").copy()'
)
[docs]class Colormap:
"""
Baseclass for all scalar to RGBA mappings.
Typically, Colormap instances are used to convert data values (floats)
from the interval ``[0, 1]`` to the RGBA color that the respective
Colormap represents. For scaling of data into the ``[0, 1]`` interval see
`matplotlib.colors.Normalize`. Subclasses of `matplotlib.cm.ScalarMappable`
make heavy use of this ``data -> normalize -> map-to-color`` processing
chain.
"""
[docs] def __init__(self, name, N=256):
"""
Parameters
----------
name : str
The name of the colormap.
N : int
The number of rgb quantization levels.
"""
self.name = name
self.N = int(N) # ensure that N is always int
self._rgba_bad = (0.0, 0.0, 0.0, 0.0) # If bad, don't paint anything.
self._rgba_under = None
self._rgba_over = None
self._i_under = self.N
self._i_over = self.N + 1
self._i_bad = self.N + 2
self._isinit = False
#: When this colormap exists on a scalar mappable and colorbar_extend
#: is not False, colorbar creation will pick up ``colorbar_extend`` as
#: the default value for the ``extend`` keyword in the
#: `matplotlib.colorbar.Colorbar` constructor.
self.colorbar_extend = False
[docs] def __call__(self, X, alpha=None, bytes=False):
"""
Parameters
----------
X : float or int, ndarray or scalar
The data value(s) to convert to RGBA.
For floats, X should be in the interval ``[0.0, 1.0]`` to
return the RGBA values ``X*100`` percent along the Colormap line.
For integers, X should be in the interval ``[0, Colormap.N)`` to
return RGBA values *indexed* from the Colormap with index ``X``.
alpha : float or array-like or None
Alpha must be a scalar between 0 and 1, a sequence of such
floats with shape matching X, or None.
bytes : bool
If False (default), the returned RGBA values will be floats in the
interval ``[0, 1]`` otherwise they will be uint8s in the interval
``[0, 255]``.
Returns
-------
Tuple of RGBA values if X is scalar, otherwise an array of
RGBA values with a shape of ``X.shape + (4, )``.
"""
if not self._isinit:
self._init()
mask_bad = X.mask if np.ma.is_masked(X) else np.isnan(X) # Mask nan's.
xa = np.array(X, copy=True)
if not xa.dtype.isnative:
xa = xa.byteswap().newbyteorder() # Native byteorder is faster.
if xa.dtype.kind == "f":
with np.errstate(invalid="ignore"):
xa *= self.N
# Negative values are out of range, but astype(int) would
# truncate them towards zero.
xa[xa < 0] = -1
# xa == 1 (== N after multiplication) is not out of range.
xa[xa == self.N] = self.N - 1
# Avoid converting large positive values to negative integers.
np.clip(xa, -1, self.N, out=xa)
xa = xa.astype(int)
# Set the over-range indices before the under-range;
# otherwise the under-range values get converted to over-range.
xa[xa > self.N - 1] = self._i_over
xa[xa < 0] = self._i_under
xa[mask_bad] = self._i_bad
if bytes:
lut = (self._lut * 255).astype(np.uint8)
else:
lut = self._lut.copy() # Don't let alpha modify original _lut.
rgba = np.empty(shape=xa.shape + (4,), dtype=lut.dtype)
lut.take(xa, axis=0, mode='clip', out=rgba)
if alpha is not None:
if np.iterable(alpha):
alpha = np.asarray(alpha)
if alpha.shape != xa.shape:
raise ValueError("alpha is array-like but its shape"
" %s doesn't match that of X %s" %
(alpha.shape, xa.shape))
alpha = np.clip(alpha, 0, 1)
if bytes:
alpha = (alpha * 255).astype(np.uint8)
rgba[..., -1] = alpha
# If the "bad" color is all zeros, then ignore alpha input.
if (lut[-1] == 0).all() and np.any(mask_bad):
if np.iterable(mask_bad) and mask_bad.shape == xa.shape:
rgba[mask_bad] = (0, 0, 0, 0)
else:
rgba[..., :] = (0, 0, 0, 0)
if not np.iterable(X):
rgba = tuple(rgba)
return rgba
[docs] def __copy__(self):
cls = self.__class__
cmapobject = cls.__new__(cls)
cmapobject.__dict__.update(self.__dict__)
if self._isinit:
cmapobject._lut = np.copy(self._lut)
cmapobject._global = False
return cmapobject
[docs] def get_bad(self):
"""Get the color for masked values."""
if not self._isinit:
self._init()
return np.array(self._lut[self._i_bad])
[docs] def set_bad(self, color='k', alpha=None):
"""Set the color for masked values."""
_warn_if_global_cmap_modified(self)
self._rgba_bad = to_rgba(color, alpha)
if self._isinit:
self._set_extremes()
[docs] def get_under(self):
"""Get the color for low out-of-range values."""
if not self._isinit:
self._init()
return np.array(self._lut[self._i_under])
[docs] def set_under(self, color='k', alpha=None):
"""Set the color for low out-of-range values."""
_warn_if_global_cmap_modified(self)
self._rgba_under = to_rgba(color, alpha)
if self._isinit:
self._set_extremes()
[docs] def get_over(self):
"""Get the color for high out-of-range values."""
if not self._isinit:
self._init()
return np.array(self._lut[self._i_over])
[docs] def set_over(self, color='k', alpha=None):
"""Set the color for high out-of-range values."""
_warn_if_global_cmap_modified(self)
self._rgba_over = to_rgba(color, alpha)
if self._isinit:
self._set_extremes()
[docs] def set_extremes(self, *, bad=None, under=None, over=None):
"""
Set the colors for masked (*bad*) values and, when ``norm.clip =
False``, low (*under*) and high (*over*) out-of-range values.
"""
if bad is not None:
self.set_bad(bad)
if under is not None:
self.set_under(under)
if over is not None:
self.set_over(over)
[docs] def with_extremes(self, *, bad=None, under=None, over=None):
"""
Return a copy of the colormap, for which the colors for masked (*bad*)
values and, when ``norm.clip = False``, low (*under*) and high (*over*)
out-of-range values, have been set accordingly.
"""
new_cm = copy.copy(self)
new_cm.set_extremes(bad=bad, under=under, over=over)
return new_cm
def _set_extremes(self):
if self._rgba_under:
self._lut[self._i_under] = self._rgba_under
else:
self._lut[self._i_under] = self._lut[0]
if self._rgba_over:
self._lut[self._i_over] = self._rgba_over
else:
self._lut[self._i_over] = self._lut[self.N - 1]
self._lut[self._i_bad] = self._rgba_bad
def _init(self):
"""Generate the lookup table, ``self._lut``."""
raise NotImplementedError("Abstract class only")
[docs] def is_gray(self):
"""Return whether the colormap is grayscale."""
if not self._isinit:
self._init()
return (np.all(self._lut[:, 0] == self._lut[:, 1]) and
np.all(self._lut[:, 0] == self._lut[:, 2]))
def _resample(self, lutsize):
"""Return a new colormap with *lutsize* entries."""
raise NotImplementedError()
[docs] def reversed(self, name=None):
"""
Return a reversed instance of the Colormap.
.. note:: This function is not implemented for base class.
Parameters
----------
name : str, optional
The name for the reversed colormap. If it's None the
name will be the name of the parent colormap + "_r".
See Also
--------
LinearSegmentedColormap.reversed
ListedColormap.reversed
"""
raise NotImplementedError()
def _repr_png_(self):
"""Generate a PNG representation of the Colormap."""
X = np.tile(np.linspace(0, 1, _REPR_PNG_SIZE[0]),
(_REPR_PNG_SIZE[1], 1))
pixels = self(X, bytes=True)
png_bytes = io.BytesIO()
title = self.name + ' colormap'
author = f'Matplotlib v{mpl.__version__}, https://matplotlib.org'
pnginfo = PngInfo()
pnginfo.add_text('Title', title)
pnginfo.add_text('Description', title)
pnginfo.add_text('Author', author)
pnginfo.add_text('Software', author)
Image.fromarray(pixels).save(png_bytes, format='png', pnginfo=pnginfo)
return png_bytes.getvalue()
def _repr_html_(self):
"""Generate an HTML representation of the Colormap."""
png_bytes = self._repr_png_()
png_base64 = base64.b64encode(png_bytes).decode('ascii')
def color_block(color):
hex_color = to_hex(color, keep_alpha=True)
return (f'<div title="{hex_color}" '
'style="display: inline-block; '
'width: 1em; height: 1em; '
'margin: 0; '
'vertical-align: middle; '
'border: 1px solid #555; '
f'background-color: {hex_color};"></div>')
return ('<div style="vertical-align: middle;">'
f'<strong>{self.name}</strong> '
'</div>'
'<div class="cmap"><img '
f'alt="{self.name} colormap" '
f'title="{self.name}" '
'style="border: 1px solid #555;" '
f'src="data:image/png;base64,{png_base64}"></div>'
'<div style="vertical-align: middle; '
f'max-width: {_REPR_PNG_SIZE[0]+2}px; '
'display: flex; justify-content: space-between;">'
'<div style="float: left;">'
f'{color_block(self.get_under())} under'
'</div>'
'<div style="margin: 0 auto; display: inline-block;">'
f'bad {color_block(self.get_bad())}'
'</div>'
'<div style="float: right;">'
f'over {color_block(self.get_over())}'
'</div>')
[docs] def copy(self):
"""Return a copy of the colormap."""
return self.__copy__()
[docs]class LinearSegmentedColormap(Colormap):
"""
Colormap objects based on lookup tables using linear segments.
The lookup table is generated using linear interpolation for each
primary color, with the 0-1 domain divided into any number of
segments.
"""
[docs] def __init__(self, name, segmentdata, N=256, gamma=1.0):
"""
Create colormap from linear mapping segments
segmentdata argument is a dictionary with a red, green and blue
entries. Each entry should be a list of *x*, *y0*, *y1* tuples,
forming rows in a table. Entries for alpha are optional.
Example: suppose you want red to increase from 0 to 1 over
the bottom half, green to do the same over the middle half,
and blue over the top half. Then you would use::
cdict = {'red': [(0.0, 0.0, 0.0),
(0.5, 1.0, 1.0),
(1.0, 1.0, 1.0)],
'green': [(0.0, 0.0, 0.0),
(0.25, 0.0, 0.0),
(0.75, 1.0, 1.0),
(1.0, 1.0, 1.0)],
'blue': [(0.0, 0.0, 0.0),
(0.5, 0.0, 0.0),
(1.0, 1.0, 1.0)]}
Each row in the table for a given color is a sequence of
*x*, *y0*, *y1* tuples. In each sequence, *x* must increase
monotonically from 0 to 1. For any input value *z* falling
between *x[i]* and *x[i+1]*, the output value of a given color
will be linearly interpolated between *y1[i]* and *y0[i+1]*::
row i: x y0 y1
/
/
row i+1: x y0 y1
Hence y0 in the first row and y1 in the last row are never used.
See Also
--------
LinearSegmentedColormap.from_list
Static method; factory function for generating a smoothly-varying
LinearSegmentedColormap.
"""
# True only if all colors in map are identical; needed for contouring.
self.monochrome = False
super().__init__(name, N)
self._segmentdata = segmentdata
self._gamma = gamma
def _init(self):
self._lut = np.ones((self.N + 3, 4), float)
self._lut[:-3, 0] = _create_lookup_table(
self.N, self._segmentdata['red'], self._gamma)
self._lut[:-3, 1] = _create_lookup_table(
self.N, self._segmentdata['green'], self._gamma)
self._lut[:-3, 2] = _create_lookup_table(
self.N, self._segmentdata['blue'], self._gamma)
if 'alpha' in self._segmentdata:
self._lut[:-3, 3] = _create_lookup_table(
self.N, self._segmentdata['alpha'], 1)
self._isinit = True
self._set_extremes()
[docs] def set_gamma(self, gamma):
"""Set a new gamma value and regenerate colormap."""
self._gamma = gamma
self._init()
[docs] @staticmethod
def from_list(name, colors, N=256, gamma=1.0):
"""
Create a `LinearSegmentedColormap` from a list of colors.
Parameters
----------
name : str
The name of the colormap.
colors : array-like of colors or array-like of (value, color)
If only colors are given, they are equidistantly mapped from the
range :math:`[0, 1]`; i.e. 0 maps to ``colors[0]`` and 1 maps to
``colors[-1]``.
If (value, color) pairs are given, the mapping is from *value*
to *color*. This can be used to divide the range unevenly.
N : int
The number of rgb quantization levels.
gamma : float
"""
if not np.iterable(colors):
raise ValueError('colors must be iterable')
if (isinstance(colors[0], Sized) and len(colors[0]) == 2
and not isinstance(colors[0], str)):
# List of value, color pairs
vals, colors = zip(*colors)
else:
vals = np.linspace(0, 1, len(colors))
r, g, b, a = to_rgba_array(colors).T
cdict = {
"red": np.column_stack([vals, r, r]),
"green": np.column_stack([vals, g, g]),
"blue": np.column_stack([vals, b, b]),
"alpha": np.column_stack([vals, a, a]),
}
return LinearSegmentedColormap(name, cdict, N, gamma)
def _resample(self, lutsize):
"""Return a new colormap with *lutsize* entries."""
new_cmap = LinearSegmentedColormap(self.name, self._segmentdata,
lutsize)
new_cmap._rgba_over = self._rgba_over
new_cmap._rgba_under = self._rgba_under
new_cmap._rgba_bad = self._rgba_bad
return new_cmap
# Helper ensuring picklability of the reversed cmap.
@staticmethod
def _reverser(func, x):
return func(1 - x)
[docs] def reversed(self, name=None):
"""
Return a reversed instance of the Colormap.
Parameters
----------
name : str, optional
The name for the reversed colormap. If it's None the
name will be the name of the parent colormap + "_r".
Returns
-------
LinearSegmentedColormap
The reversed colormap.
"""
if name is None:
name = self.name + "_r"
# Using a partial object keeps the cmap picklable.
data_r = {key: (functools.partial(self._reverser, data)
if callable(data) else
[(1.0 - x, y1, y0) for x, y0, y1 in reversed(data)])
for key, data in self._segmentdata.items()}
new_cmap = LinearSegmentedColormap(name, data_r, self.N, self._gamma)
# Reverse the over/under values too
new_cmap._rgba_over = self._rgba_under
new_cmap._rgba_under = self._rgba_over
new_cmap._rgba_bad = self._rgba_bad
return new_cmap
[docs]class ListedColormap(Colormap):
"""
Colormap object generated from a list of colors.
This may be most useful when indexing directly into a colormap,
but it can also be used to generate special colormaps for ordinary
mapping.
Parameters
----------
colors : list, array
List of Matplotlib color specifications, or an equivalent Nx3 or Nx4
floating point array (*N* rgb or rgba values).
name : str, optional
String to identify the colormap.
N : int, optional
Number of entries in the map. The default is *None*, in which case
there is one colormap entry for each element in the list of colors.
If ::
N < len(colors)
the list will be truncated at *N*. If ::
N > len(colors)
the list will be extended by repetition.
"""
[docs] def __init__(self, colors, name='from_list', N=None):
self.monochrome = False # Are all colors identical? (for contour.py)
if N is None:
self.colors = colors
N = len(colors)
else:
if isinstance(colors, str):
self.colors = [colors] * N
self.monochrome = True
elif np.iterable(colors):
if len(colors) == 1:
self.monochrome = True
self.colors = list(
itertools.islice(itertools.cycle(colors), N))
else:
try:
gray = float(colors)
except TypeError:
pass
else:
self.colors = [gray] * N
self.monochrome = True
super().__init__(name, N)
def _init(self):
self._lut = np.zeros((self.N + 3, 4), float)
self._lut[:-3] = to_rgba_array(self.colors)
self._isinit = True
self._set_extremes()
def _resample(self, lutsize):
"""Return a new colormap with *lutsize* entries."""
colors = self(np.linspace(0, 1, lutsize))
new_cmap = ListedColormap(colors, name=self.name)
# Keep the over/under values too
new_cmap._rgba_over = self._rgba_over
new_cmap._rgba_under = self._rgba_under
new_cmap._rgba_bad = self._rgba_bad
return new_cmap
[docs] def reversed(self, name=None):
"""
Return a reversed instance of the Colormap.
Parameters
----------
name : str, optional
The name for the reversed colormap. If it's None the
name will be the name of the parent colormap + "_r".
Returns
-------
ListedColormap
A reversed instance of the colormap.
"""
if name is None:
name = self.name + "_r"
colors_r = list(reversed(self.colors))
new_cmap = ListedColormap(colors_r, name=name, N=self.N)
# Reverse the over/under values too
new_cmap._rgba_over = self._rgba_under
new_cmap._rgba_under = self._rgba_over
new_cmap._rgba_bad = self._rgba_bad
return new_cmap
[docs]class Normalize:
"""
A class which, when called, linearly normalizes data into the
``[0.0, 1.0]`` interval.
"""
[docs] def __init__(self, vmin=None, vmax=None, clip=False):
"""
Parameters
----------
vmin, vmax : float or None
If *vmin* and/or *vmax* is not given, they are initialized from the
minimum and maximum value, respectively, of the first input
processed; i.e., ``__call__(A)`` calls ``autoscale_None(A)``.
clip : bool, default: False
If ``True`` values falling outside the range ``[vmin, vmax]``,
are mapped to 0 or 1, whichever is closer, and masked values are
set to 1. If ``False`` masked values remain masked.
Clipping silently defeats the purpose of setting the over, under,
and masked colors in a colormap, so it is likely to lead to
surprises; therefore the default is ``clip=False``.
Notes
-----
Returns 0 if ``vmin == vmax``.
"""
self.vmin = _sanitize_extrema(vmin)
self.vmax = _sanitize_extrema(vmax)
self.clip = clip
self._scale = scale.LinearScale(axis=None)
[docs] @staticmethod
def process_value(value):
"""
Homogenize the input *value* for easy and efficient normalization.
*value* can be a scalar or sequence.
Returns
-------
result : masked array
Masked array with the same shape as *value*.
is_scalar : bool
Whether *value* is a scalar.
Notes
-----
Float dtypes are preserved; integer types with two bytes or smaller are
converted to np.float32, and larger types are converted to np.float64.
Preserving float32 when possible, and using in-place operations,
greatly improves speed for large arrays.
"""
is_scalar = not np.iterable(value)
if is_scalar:
value = [value]
dtype = np.min_scalar_type(value)
if np.issubdtype(dtype, np.integer) or dtype.type is np.bool_:
# bool_/int8/int16 -> float32; int32/int64 -> float64
dtype = np.promote_types(dtype, np.float32)
# ensure data passed in as an ndarray subclass are interpreted as
# an ndarray. See issue #6622.
mask = np.ma.getmask(value)
data = np.asarray(value)
result = np.ma.array(data, mask=mask, dtype=dtype, copy=True)
return result, is_scalar
[docs] def __call__(self, value, clip=None):
"""
Normalize *value* data in the ``[vmin, vmax]`` interval into the
``[0.0, 1.0]`` interval and return it.
Parameters
----------
value
Data to normalize.
clip : bool
If ``None``, defaults to ``self.clip`` (which defaults to
``False``).
Notes
-----
If not already initialized, ``self.vmin`` and ``self.vmax`` are
initialized using ``self.autoscale_None(value)``.
"""
if clip is None:
clip = self.clip
result, is_scalar = self.process_value(value)
self.autoscale_None(result)
# Convert at least to float, without losing precision.
(vmin,), _ = self.process_value(self.vmin)
(vmax,), _ = self.process_value(self.vmax)
if vmin == vmax:
result.fill(0) # Or should it be all masked? Or 0.5?
elif vmin > vmax:
raise ValueError("minvalue must be less than or equal to maxvalue")
else:
if clip:
mask = np.ma.getmask(result)
result = np.ma.array(np.clip(result.filled(vmax), vmin, vmax),
mask=mask)
# ma division is very slow; we can take a shortcut
resdat = result.data
resdat -= vmin
resdat /= (vmax - vmin)
result = np.ma.array(resdat, mask=result.mask, copy=False)
if is_scalar:
result = result[0]
return result
[docs] def inverse(self, value):
if not self.scaled():
raise ValueError("Not invertible until both vmin and vmax are set")
(vmin,), _ = self.process_value(self.vmin)
(vmax,), _ = self.process_value(self.vmax)
if np.iterable(value):
val = np.ma.asarray(value)
return vmin + val * (vmax - vmin)
else:
return vmin + value * (vmax - vmin)
[docs] def autoscale(self, A):
"""Set *vmin*, *vmax* to min, max of *A*."""
A = np.asanyarray(A)
self.vmin = A.min()
self.vmax = A.max()
[docs] def autoscale_None(self, A):
"""If vmin or vmax are not set, use the min/max of *A* to set them."""
A = np.asanyarray(A)
if self.vmin is None and A.size:
self.vmin = A.min()
if self.vmax is None and A.size:
self.vmax = A.max()
[docs] def scaled(self):
"""Return whether vmin and vmax are set."""
return self.vmin is not None and self.vmax is not None
[docs]class TwoSlopeNorm(Normalize):
[docs] def __init__(self, vcenter, vmin=None, vmax=None):
"""
Normalize data with a set center.
Useful when mapping data with an unequal rates of change around a
conceptual center, e.g., data that range from -2 to 4, with 0 as
the midpoint.
Parameters
----------
vcenter : float
The data value that defines ``0.5`` in the normalization.
vmin : float, optional
The data value that defines ``0.0`` in the normalization.
Defaults to the min value of the dataset.
vmax : float, optional
The data value that defines ``1.0`` in the normalization.
Defaults to the the max value of the dataset.
Examples
--------
This maps data value -4000 to 0., 0 to 0.5, and +10000 to 1.0; data
between is linearly interpolated::
>>> import matplotlib.colors as mcolors
>>> offset = mcolors.TwoSlopeNorm(vmin=-4000.,
vcenter=0., vmax=10000)
>>> data = [-4000., -2000., 0., 2500., 5000., 7500., 10000.]
>>> offset(data)
array([0., 0.25, 0.5, 0.625, 0.75, 0.875, 1.0])
"""
self.vcenter = vcenter
self.vmin = vmin
self.vmax = vmax
if vcenter is not None and vmax is not None and vcenter >= vmax:
raise ValueError('vmin, vcenter, and vmax must be in '
'ascending order')
if vcenter is not None and vmin is not None and vcenter <= vmin:
raise ValueError('vmin, vcenter, and vmax must be in '
'ascending order')
[docs] def autoscale_None(self, A):
"""
Get vmin and vmax, and then clip at vcenter
"""
super().autoscale_None(A)
if self.vmin > self.vcenter:
self.vmin = self.vcenter
if self.vmax < self.vcenter:
self.vmax = self.vcenter
[docs] def __call__(self, value, clip=None):
"""
Map value to the interval [0, 1]. The clip argument is unused.
"""
result, is_scalar = self.process_value(value)
self.autoscale_None(result) # sets self.vmin, self.vmax if None
if not self.vmin <= self.vcenter <= self.vmax:
raise ValueError("vmin, vcenter, vmax must increase monotonically")
result = np.ma.masked_array(
np.interp(result, [self.vmin, self.vcenter, self.vmax],
[0, 0.5, 1.]), mask=np.ma.getmask(result))
if is_scalar:
result = np.atleast_1d(result)[0]
return result
[docs]class CenteredNorm(Normalize):
[docs] def __init__(self, vcenter=0, halfrange=None, clip=False):
"""
Normalize symmetrical data around a center (0 by default).
Unlike `TwoSlopeNorm`, `CenteredNorm` applies an equal rate of change
around the center.
Useful when mapping symmetrical data around a conceptual center
e.g., data that range from -2 to 4, with 0 as the midpoint, and
with equal rates of change around that midpoint.
Parameters
----------
vcenter : float, default: 0
The data value that defines ``0.5`` in the normalization.
halfrange : float, optional
The range of data values that defines a range of ``0.5`` in the
normalization, so that *vcenter* - *halfrange* is ``0.0`` and
*vcenter* + *halfrange* is ``1.0`` in the normalization.
Defaults to the largest absolute difference to *vcenter* for
the values in the dataset.
Examples
--------
This maps data values -2 to 0.25, 0 to 0.5, and 4 to 1.0
(assuming equal rates of change above and below 0.0):
>>> import matplotlib.colors as mcolors
>>> norm = mcolors.CenteredNorm(halfrange=4.0)
>>> data = [-2., 0., 4.]
>>> norm(data)
array([0.25, 0.5 , 1. ])
"""
self._vcenter = vcenter
# calling the halfrange setter to set vmin and vmax
self.halfrange = halfrange
self.clip = clip
def _set_vmin_vmax(self):
"""
Set *vmin* and *vmax* based on *vcenter* and *halfrange*.
"""
self.vmax = self._vcenter + self._halfrange
self.vmin = self._vcenter - self._halfrange
[docs] def autoscale(self, A):
"""
Set *halfrange* to ``max(abs(A-vcenter))``, then set *vmin* and *vmax*.
"""
A = np.asanyarray(A)
self._halfrange = max(self._vcenter-A.min(),
A.max()-self._vcenter)
self._set_vmin_vmax()
[docs] def autoscale_None(self, A):
"""Set *vmin* and *vmax*."""
A = np.asanyarray(A)
if self.vmax is None and A.size:
self.autoscale(A)
@property
def vcenter(self):
return self._vcenter
@vcenter.setter
def vcenter(self, vcenter):
self._vcenter = vcenter
if self.vmax is not None:
# recompute halfrange assuming vmin and vmax represent
# min and max of data
self._halfrange = max(self._vcenter-self.vmin,
self.vmax-self._vcenter)
self._set_vmin_vmax()
@property
def halfrange(self):
return self._halfrange
@halfrange.setter
def halfrange(self, halfrange):
if halfrange is None:
self._halfrange = None
self.vmin = None
self.vmax = None
else:
self._halfrange = abs(halfrange)
[docs] def __call__(self, value, clip=None):
if self._halfrange is not None:
# enforce symmetry, reset vmin and vmax
self._set_vmin_vmax()
return super().__call__(value, clip=clip)
def _make_norm_from_scale(scale_cls, base_norm_cls=None, *, init=None):
"""
Decorator for building a `.Normalize` subclass from a `.Scale` subclass.
After ::
@_make_norm_from_scale(scale_cls)
class norm_cls(Normalize):
...
*norm_cls* is filled with methods so that normalization computations are
forwarded to *scale_cls* (i.e., *scale_cls* is the scale that would be used
for the colorbar of a mappable normalized with *norm_cls*).
If *init* is not passed, then the constructor signature of *norm_cls*
will be ``norm_cls(vmin=None, vmax=None, clip=False)``; these three
parameters will be forwarded to the base class (``Normalize.__init__``),
and a *scale_cls* object will be initialized with no arguments (other than
a dummy axis).
If the *scale_cls* constructor takes additional parameters, then *init*
should be passed to `_make_norm_from_scale`. It is a callable which is
*only* used for its signature. First, this signature will become the
signature of *norm_cls*. Second, the *norm_cls* constructor will bind the
parameters passed to it using this signature, extract the bound *vmin*,
*vmax*, and *clip* values, pass those to ``Normalize.__init__``, and
forward the remaining bound values (including any defaults defined by the
signature) to the *scale_cls* constructor.
"""
if base_norm_cls is None:
return functools.partial(_make_norm_from_scale, scale_cls, init=init)
if init is None:
def init(vmin=None, vmax=None, clip=False): pass
bound_init_signature = inspect.signature(init)
class Norm(base_norm_cls):
def __init__(self, *args, **kwargs):
ba = bound_init_signature.bind(*args, **kwargs)
ba.apply_defaults()
super().__init__(
**{k: ba.arguments.pop(k) for k in ["vmin", "vmax", "clip"]})
self._scale = scale_cls(axis=None, **ba.arguments)
self._trf = self._scale.get_transform()
def __call__(self, value, clip=None):
value, is_scalar = self.process_value(value)
self.autoscale_None(value)
if self.vmin > self.vmax:
raise ValueError("vmin must be less or equal to vmax")
if self.vmin == self.vmax:
return np.full_like(value, 0)
if clip is None:
clip = self.clip
if clip:
value = np.clip(value, self.vmin, self.vmax)
t_value = self._trf.transform(value).reshape(np.shape(value))
t_vmin, t_vmax = self._trf.transform([self.vmin, self.vmax])
if not np.isfinite([t_vmin, t_vmax]).all():
raise ValueError("Invalid vmin or vmax")
t_value -= t_vmin
t_value /= (t_vmax - t_vmin)
t_value = np.ma.masked_invalid(t_value, copy=False)
return t_value[0] if is_scalar else t_value
def inverse(self, value):
if not self.scaled():
raise ValueError("Not invertible until scaled")
if self.vmin > self.vmax:
raise ValueError("vmin must be less or equal to vmax")
t_vmin, t_vmax = self._trf.transform([self.vmin, self.vmax])
if not np.isfinite([t_vmin, t_vmax]).all():
raise ValueError("Invalid vmin or vmax")
value, is_scalar = self.process_value(value)
rescaled = value * (t_vmax - t_vmin)
rescaled += t_vmin
value = (self._trf
.inverted()
.transform(rescaled)
.reshape(np.shape(value)))
return value[0] if is_scalar else value
Norm.__name__ = base_norm_cls.__name__
Norm.__qualname__ = base_norm_cls.__qualname__
Norm.__module__ = base_norm_cls.__module__
Norm.__init__.__signature__ = bound_init_signature.replace(parameters=[
inspect.Parameter("self", inspect.Parameter.POSITIONAL_OR_KEYWORD),
*bound_init_signature.parameters.values()])
return Norm
[docs]@_make_norm_from_scale(
scale.FuncScale,
init=lambda functions, vmin=None, vmax=None, clip=False: None)
class FuncNorm(Normalize):
"""
Arbitrary normalization using functions for the forward and inverse.
Parameters
----------
functions : (callable, callable)
two-tuple of the forward and inverse functions for the normalization.
The forward function must be monotonic.
Both functions must have the signature ::
def forward(values: array-like) -> array-like
vmin, vmax : float or None
If *vmin* and/or *vmax* is not given, they are initialized from the
minimum and maximum value, respectively, of the first input
processed; i.e., ``__call__(A)`` calls ``autoscale_None(A)``.
clip : bool, default: False
If ``True`` values falling outside the range ``[vmin, vmax]``,
are mapped to 0 or 1, whichever is closer, and masked values are
set to 1. If ``False`` masked values remain masked.
Clipping silently defeats the purpose of setting the over, under,
and masked colors in a colormap, so it is likely to lead to
surprises; therefore the default is ``clip=False``.
"""
[docs]@_make_norm_from_scale(functools.partial(scale.LogScale, nonpositive="mask"))
class LogNorm(Normalize):
"""Normalize a given value to the 0-1 range on a log scale."""
def autoscale(self, A):
# docstring inherited.
super().autoscale(np.ma.masked_less_equal(A, 0, copy=False))
def autoscale_None(self, A):
# docstring inherited.
super().autoscale_None(np.ma.masked_less_equal(A, 0, copy=False))
[docs]@_make_norm_from_scale(
scale.SymmetricalLogScale,
init=lambda linthresh, linscale=1., vmin=None, vmax=None, clip=False, *,
base=10: None)
class SymLogNorm(Normalize):
"""
The symmetrical logarithmic scale is logarithmic in both the
positive and negative directions from the origin.
Since the values close to zero tend toward infinity, there is a
need to have a range around zero that is linear. The parameter
*linthresh* allows the user to specify the size of this range
(-*linthresh*, *linthresh*).
Parameters
----------
linthresh : float
The range within which the plot is linear (to avoid having the plot
go to infinity around zero).
linscale : float, default: 1
This allows the linear range (-*linthresh* to *linthresh*) to be
stretched relative to the logarithmic range. Its value is the
number of decades to use for each half of the linear range. For
example, when *linscale* == 1.0 (the default), the space used for
the positive and negative halves of the linear range will be equal
to one decade in the logarithmic range.
base : float, default: 10
"""
@property
def linthresh(self):
return self._scale.linthresh
@linthresh.setter
def linthresh(self, value):
self._scale.linthresh = value
[docs]class PowerNorm(Normalize):
"""
Linearly map a given value to the 0-1 range and then apply
a power-law normalization over that range.
"""
[docs] def __init__(self, gamma, vmin=None, vmax=None, clip=False):
super().__init__(vmin, vmax, clip)
self.gamma = gamma
[docs] def __call__(self, value, clip=None):
if clip is None:
clip = self.clip
result, is_scalar = self.process_value(value)
self.autoscale_None(result)
gamma = self.gamma
vmin, vmax = self.vmin, self.vmax
if vmin > vmax:
raise ValueError("minvalue must be less than or equal to maxvalue")
elif vmin == vmax:
result.fill(0)
else:
if clip:
mask = np.ma.getmask(result)
result = np.ma.array(np.clip(result.filled(vmax), vmin, vmax),
mask=mask)
resdat = result.data
resdat -= vmin
resdat[resdat < 0] = 0
np.power(resdat, gamma, resdat)
resdat /= (vmax - vmin) ** gamma
result = np.ma.array(resdat, mask=result.mask, copy=False)
if is_scalar:
result = result[0]
return result
[docs] def inverse(self, value):
if not self.scaled():
raise ValueError("Not invertible until scaled")
gamma = self.gamma
vmin, vmax = self.vmin, self.vmax
if np.iterable(value):
val = np.ma.asarray(value)
return np.ma.power(val, 1. / gamma) * (vmax - vmin) + vmin
else:
return pow(value, 1. / gamma) * (vmax - vmin) + vmin
[docs]class BoundaryNorm(Normalize):
"""
Generate a colormap index based on discrete intervals.
Unlike `Normalize` or `LogNorm`, `BoundaryNorm` maps values to integers
instead of to the interval 0-1.
Mapping to the 0-1 interval could have been done via piece-wise linear
interpolation, but using integers seems simpler, and reduces the number of
conversions back and forth between integer and floating point.
"""
[docs] def __init__(self, boundaries, ncolors, clip=False, *, extend='neither'):
"""
Parameters
----------
boundaries : array-like
Monotonically increasing sequence of at least 2 boundaries.
ncolors : int
Number of colors in the colormap to be used.
clip : bool, optional
If clip is ``True``, out of range values are mapped to 0 if they
are below ``boundaries[0]`` or mapped to ``ncolors - 1`` if they
are above ``boundaries[-1]``.
If clip is ``False``, out of range values are mapped to -1 if
they are below ``boundaries[0]`` or mapped to *ncolors* if they are
above ``boundaries[-1]``. These are then converted to valid indices
by `Colormap.__call__`.
extend : {'neither', 'both', 'min', 'max'}, default: 'neither'
Extend the number of bins to include one or both of the
regions beyond the boundaries. For example, if ``extend``
is 'min', then the color to which the region between the first
pair of boundaries is mapped will be distinct from the first
color in the colormap, and by default a
`~matplotlib.colorbar.Colorbar` will be drawn with
the triangle extension on the left or lower end.
Returns
-------
int16 scalar or array
Notes
-----
*boundaries* defines the edges of bins, and data falling within a bin
is mapped to the color with the same index.
If the number of bins, including any extensions, is less than
*ncolors*, the color index is chosen by linear interpolation, mapping
the ``[0, nbins - 1]`` range onto the ``[0, ncolors - 1]`` range.
"""
if clip and extend != 'neither':
raise ValueError("'clip=True' is not compatible with 'extend'")
self.clip = clip
self.vmin = boundaries[0]
self.vmax = boundaries[-1]
self.boundaries = np.asarray(boundaries)
self.N = len(self.boundaries)
if self.N < 2:
raise ValueError("You must provide at least 2 boundaries "
f"(1 region) but you passed in {boundaries!r}")
self.Ncmap = ncolors
self.extend = extend
self._scale = None # don't use the default scale.
self._n_regions = self.N - 1 # number of colors needed
self._offset = 0
if extend in ('min', 'both'):
self._n_regions += 1
self._offset = 1
if extend in ('max', 'both'):
self._n_regions += 1
if self._n_regions > self.Ncmap:
raise ValueError(f"There are {self._n_regions} color bins "
"including extensions, but ncolors = "
f"{ncolors}; ncolors must equal or exceed the "
"number of bins")
[docs] def __call__(self, value, clip=None):
if clip is None:
clip = self.clip
xx, is_scalar = self.process_value(value)
mask = np.ma.getmaskarray(xx)
# Fill masked values a value above the upper boundary
xx = np.atleast_1d(xx.filled(self.vmax + 1))
if clip:
np.clip(xx, self.vmin, self.vmax, out=xx)
max_col = self.Ncmap - 1
else:
max_col = self.Ncmap
# this gives us the bins in the lookup table in the range
# [0, _n_regions - 1] (the offset is baked in in the init)
iret = np.digitize(xx, self.boundaries) - 1 + self._offset
# if we have more colors than regions, stretch the region
# index computed above to full range of the color bins. This
# will make use of the full range (but skip some of the colors
# in the middle) such that the first region is mapped to the
# first color and the last region is mapped to the last color.
if self.Ncmap > self._n_regions:
if self._n_regions == 1:
# special case the 1 region case, pick the middle color
iret[iret == 0] = (self.Ncmap - 1) // 2
else:
# otherwise linearly remap the values from the region index
# to the color index spaces
iret = (self.Ncmap - 1) / (self._n_regions - 1) * iret
# cast to 16bit integers in all cases
iret = iret.astype(np.int16)
iret[xx < self.vmin] = -1
iret[xx >= self.vmax] = max_col
ret = np.ma.array(iret, mask=mask)
if is_scalar:
ret = int(ret[0]) # assume python scalar
return ret
[docs] def inverse(self, value):
"""
Raises
------
ValueError
BoundaryNorm is not invertible, so calling this method will always
raise an error
"""
raise ValueError("BoundaryNorm is not invertible")
[docs]class NoNorm(Normalize):
"""
Dummy replacement for `Normalize`, for the case where we want to use
indices directly in a `~matplotlib.cm.ScalarMappable`.
"""
[docs] def __call__(self, value, clip=None):
return value
[docs] def inverse(self, value):
return value
[docs]def rgb_to_hsv(arr):
"""
Convert float rgb values (in the range [0, 1]), in a numpy array to hsv
values.
Parameters
----------
arr : (..., 3) array-like
All values must be in the range [0, 1]
Returns
-------
(..., 3) ndarray
Colors converted to hsv values in range [0, 1]
"""
arr = np.asarray(arr)
# check length of the last dimension, should be _some_ sort of rgb
if arr.shape[-1] != 3:
raise ValueError("Last dimension of input array must be 3; "
"shape {} was found.".format(arr.shape))
in_shape = arr.shape
arr = np.array(
arr, copy=False,
dtype=np.promote_types(arr.dtype, np.float32), # Don't work on ints.
ndmin=2, # In case input was 1D.
)
out = np.zeros_like(arr)
arr_max = arr.max(-1)
ipos = arr_max > 0
delta = arr.ptp(-1)
s = np.zeros_like(delta)
s[ipos] = delta[ipos] / arr_max[ipos]
ipos = delta > 0
# red is max
idx = (arr[..., 0] == arr_max) & ipos
out[idx, 0] = (arr[idx, 1] - arr[idx, 2]) / delta[idx]
# green is max
idx = (arr[..., 1] == arr_max) & ipos
out[idx, 0] = 2. + (arr[idx, 2] - arr[idx, 0]) / delta[idx]
# blue is max
idx = (arr[..., 2] == arr_max) & ipos
out[idx, 0] = 4. + (arr[idx, 0] - arr[idx, 1]) / delta[idx]
out[..., 0] = (out[..., 0] / 6.0) % 1.0
out[..., 1] = s
out[..., 2] = arr_max
return out.reshape(in_shape)
[docs]def hsv_to_rgb(hsv):
"""
Convert hsv values to rgb.
Parameters
----------
hsv : (..., 3) array-like
All values assumed to be in range [0, 1]
Returns
-------
(..., 3) ndarray
Colors converted to RGB values in range [0, 1]
"""
hsv = np.asarray(hsv)
# check length of the last dimension, should be _some_ sort of rgb
if hsv.shape[-1] != 3:
raise ValueError("Last dimension of input array must be 3; "
"shape {shp} was found.".format(shp=hsv.shape))
in_shape = hsv.shape
hsv = np.array(
hsv, copy=False,
dtype=np.promote_types(hsv.dtype, np.float32), # Don't work on ints.
ndmin=2, # In case input was 1D.
)
h = hsv[..., 0]
s = hsv[..., 1]
v = hsv[..., 2]
r = np.empty_like(h)
g = np.empty_like(h)
b = np.empty_like(h)
i = (h * 6.0).astype(int)
f = (h * 6.0) - i
p = v * (1.0 - s)
q = v * (1.0 - s * f)
t = v * (1.0 - s * (1.0 - f))
idx = i % 6 == 0
r[idx] = v[idx]
g[idx] = t[idx]
b[idx] = p[idx]
idx = i == 1
r[idx] = q[idx]
g[idx] = v[idx]
b[idx] = p[idx]
idx = i == 2
r[idx] = p[idx]
g[idx] = v[idx]
b[idx] = t[idx]
idx = i == 3
r[idx] = p[idx]
g[idx] = q[idx]
b[idx] = v[idx]
idx = i == 4
r[idx] = t[idx]
g[idx] = p[idx]
b[idx] = v[idx]
idx = i == 5
r[idx] = v[idx]
g[idx] = p[idx]
b[idx] = q[idx]
idx = s == 0
r[idx] = v[idx]
g[idx] = v[idx]
b[idx] = v[idx]
rgb = np.stack([r, g, b], axis=-1)
return rgb.reshape(in_shape)
def _vector_magnitude(arr):
# things that don't work here:
# * np.linalg.norm: drops mask from ma.array
# * np.sum: drops mask from ma.array unless entire vector is masked
sum_sq = 0
for i in range(arr.shape[-1]):
sum_sq += arr[..., i, np.newaxis] ** 2
return np.sqrt(sum_sq)
[docs]class LightSource:
"""
Create a light source coming from the specified azimuth and elevation.
Angles are in degrees, with the azimuth measured
clockwise from north and elevation up from the zero plane of the surface.
`shade` is used to produce "shaded" rgb values for a data array.
`shade_rgb` can be used to combine an rgb image with an elevation map.
`hillshade` produces an illumination map of a surface.
"""
[docs] def __init__(self, azdeg=315, altdeg=45, hsv_min_val=0, hsv_max_val=1,
hsv_min_sat=1, hsv_max_sat=0):
"""
Specify the azimuth (measured clockwise from south) and altitude
(measured up from the plane of the surface) of the light source
in degrees.
Parameters
----------
azdeg : float, default: 315 degrees (from the northwest)
The azimuth (0-360, degrees clockwise from North) of the light
source.
altdeg : float, default: 45 degrees
The altitude (0-90, degrees up from horizontal) of the light
source.
Notes
-----
For backwards compatibility, the parameters *hsv_min_val*,
*hsv_max_val*, *hsv_min_sat*, and *hsv_max_sat* may be supplied at
initialization as well. However, these parameters will only be used if
"blend_mode='hsv'" is passed into `shade` or `shade_rgb`.
See the documentation for `blend_hsv` for more details.
"""
self.azdeg = azdeg
self.altdeg = altdeg
self.hsv_min_val = hsv_min_val
self.hsv_max_val = hsv_max_val
self.hsv_min_sat = hsv_min_sat
self.hsv_max_sat = hsv_max_sat
@property
def direction(self):
"""The unit vector direction towards the light source."""
# Azimuth is in degrees clockwise from North. Convert to radians
# counterclockwise from East (mathematical notation).
az = np.radians(90 - self.azdeg)
alt = np.radians(self.altdeg)
return np.array([
np.cos(az) * np.cos(alt),
np.sin(az) * np.cos(alt),
np.sin(alt)
])
[docs] def hillshade(self, elevation, vert_exag=1, dx=1, dy=1, fraction=1.):
"""
Calculate the illumination intensity for a surface using the defined
azimuth and elevation for the light source.
This computes the normal vectors for the surface, and then passes them
on to `shade_normals`
Parameters
----------
elevation : 2D array-like
The height values used to generate an illumination map
vert_exag : number, optional
The amount to exaggerate the elevation values by when calculating
illumination. This can be used either to correct for differences in
units between the x-y coordinate system and the elevation
coordinate system (e.g. decimal degrees vs. meters) or to
exaggerate or de-emphasize topographic effects.
dx : number, optional
The x-spacing (columns) of the input *elevation* grid.
dy : number, optional
The y-spacing (rows) of the input *elevation* grid.
fraction : number, optional
Increases or decreases the contrast of the hillshade. Values
greater than one will cause intermediate values to move closer to
full illumination or shadow (and clipping any values that move
beyond 0 or 1). Note that this is not visually or mathematically
the same as vertical exaggeration.
Returns
-------
ndarray
A 2D array of illumination values between 0-1, where 0 is
completely in shadow and 1 is completely illuminated.
"""
# Because most image and raster GIS data has the first row in the array
# as the "top" of the image, dy is implicitly negative. This is
# consistent to what `imshow` assumes, as well.
dy = -dy
# compute the normal vectors from the partial derivatives
e_dy, e_dx = np.gradient(vert_exag * elevation, dy, dx)
# .view is to keep subclasses
normal = np.empty(elevation.shape + (3,)).view(type(elevation))
normal[..., 0] = -e_dx
normal[..., 1] = -e_dy
normal[..., 2] = 1
normal /= _vector_magnitude(normal)
return self.shade_normals(normal, fraction)
[docs] def shade_normals(self, normals, fraction=1.):
"""
Calculate the illumination intensity for the normal vectors of a
surface using the defined azimuth and elevation for the light source.
Imagine an artificial sun placed at infinity in some azimuth and
elevation position illuminating our surface. The parts of the surface
that slope toward the sun should brighten while those sides facing away
should become darker.
Parameters
----------
fraction : number, optional
Increases or decreases the contrast of the hillshade. Values
greater than one will cause intermediate values to move closer to
full illumination or shadow (and clipping any values that move
beyond 0 or 1). Note that this is not visually or mathematically
the same as vertical exaggeration.
Returns
-------
ndarray
A 2D array of illumination values between 0-1, where 0 is
completely in shadow and 1 is completely illuminated.
"""
intensity = normals.dot(self.direction)
# Apply contrast stretch
imin, imax = intensity.min(), intensity.max()
intensity *= fraction
# Rescale to 0-1, keeping range before contrast stretch
# If constant slope, keep relative scaling (i.e. flat should be 0.5,
# fully occluded 0, etc.)
if (imax - imin) > 1e-6:
# Strictly speaking, this is incorrect. Negative values should be
# clipped to 0 because they're fully occluded. However, rescaling
# in this manner is consistent with the previous implementation and
# visually appears better than a "hard" clip.
intensity -= imin
intensity /= (imax - imin)
intensity = np.clip(intensity, 0, 1)
return intensity
[docs] def shade(self, data, cmap, norm=None, blend_mode='overlay', vmin=None,
vmax=None, vert_exag=1, dx=1, dy=1, fraction=1, **kwargs):
"""
Combine colormapped data values with an illumination intensity map
(a.k.a. "hillshade") of the values.
Parameters
----------
data : 2D array-like
The height values used to generate a shaded map.
cmap : `~matplotlib.colors.Colormap`
The colormap used to color the *data* array. Note that this must be
a `~matplotlib.colors.Colormap` instance. For example, rather than
passing in ``cmap='gist_earth'``, use
``cmap=plt.get_cmap('gist_earth')`` instead.
norm : `~matplotlib.colors.Normalize` instance, optional
The normalization used to scale values before colormapping. If
None, the input will be linearly scaled between its min and max.
blend_mode : {'hsv', 'overlay', 'soft'} or callable, optional
The type of blending used to combine the colormapped data
values with the illumination intensity. Default is
"overlay". Note that for most topographic surfaces,
"overlay" or "soft" appear more visually realistic. If a
user-defined function is supplied, it is expected to
combine an MxNx3 RGB array of floats (ranging 0 to 1) with
an MxNx1 hillshade array (also 0 to 1). (Call signature
``func(rgb, illum, **kwargs)``) Additional kwargs supplied
to this function will be passed on to the *blend_mode*
function.
vmin : float or None, optional
The minimum value used in colormapping *data*. If *None* the
minimum value in *data* is used. If *norm* is specified, then this
argument will be ignored.
vmax : float or None, optional
The maximum value used in colormapping *data*. If *None* the
maximum value in *data* is used. If *norm* is specified, then this
argument will be ignored.
vert_exag : number, optional
The amount to exaggerate the elevation values by when calculating
illumination. This can be used either to correct for differences in
units between the x-y coordinate system and the elevation
coordinate system (e.g. decimal degrees vs. meters) or to
exaggerate or de-emphasize topography.
dx : number, optional
The x-spacing (columns) of the input *elevation* grid.
dy : number, optional
The y-spacing (rows) of the input *elevation* grid.
fraction : number, optional
Increases or decreases the contrast of the hillshade. Values
greater than one will cause intermediate values to move closer to
full illumination or shadow (and clipping any values that move
beyond 0 or 1). Note that this is not visually or mathematically
the same as vertical exaggeration.
Additional kwargs are passed on to the *blend_mode* function.
Returns
-------
ndarray
An MxNx4 array of floats ranging between 0-1.
"""
if vmin is None:
vmin = data.min()
if vmax is None:
vmax = data.max()
if norm is None:
norm = Normalize(vmin=vmin, vmax=vmax)
rgb0 = cmap(norm(data))
rgb1 = self.shade_rgb(rgb0, elevation=data, blend_mode=blend_mode,
vert_exag=vert_exag, dx=dx, dy=dy,
fraction=fraction, **kwargs)
# Don't overwrite the alpha channel, if present.
rgb0[..., :3] = rgb1[..., :3]
return rgb0
[docs] def shade_rgb(self, rgb, elevation, fraction=1., blend_mode='hsv',
vert_exag=1, dx=1, dy=1, **kwargs):
"""
Use this light source to adjust the colors of the *rgb* input array to
give the impression of a shaded relief map with the given *elevation*.
Parameters
----------
rgb : array-like
An (M, N, 3) RGB array, assumed to be in the range of 0 to 1.
elevation : array-like
An (M, N) array of the height values used to generate a shaded map.
fraction : number
Increases or decreases the contrast of the hillshade. Values
greater than one will cause intermediate values to move closer to
full illumination or shadow (and clipping any values that move
beyond 0 or 1). Note that this is not visually or mathematically
the same as vertical exaggeration.
blend_mode : {'hsv', 'overlay', 'soft'} or callable, optional
The type of blending used to combine the colormapped data values
with the illumination intensity. For backwards compatibility, this
defaults to "hsv". Note that for most topographic surfaces,
"overlay" or "soft" appear more visually realistic. If a
user-defined function is supplied, it is expected to combine an
MxNx3 RGB array of floats (ranging 0 to 1) with an MxNx1 hillshade
array (also 0 to 1). (Call signature
``func(rgb, illum, **kwargs)``)
Additional kwargs supplied to this function will be passed on to
the *blend_mode* function.
vert_exag : number, optional
The amount to exaggerate the elevation values by when calculating
illumination. This can be used either to correct for differences in
units between the x-y coordinate system and the elevation
coordinate system (e.g. decimal degrees vs. meters) or to
exaggerate or de-emphasize topography.
dx : number, optional
The x-spacing (columns) of the input *elevation* grid.
dy : number, optional
The y-spacing (rows) of the input *elevation* grid.
Additional kwargs are passed on to the *blend_mode* function.
Returns
-------
ndarray
An (m, n, 3) array of floats ranging between 0-1.
"""
# Calculate the "hillshade" intensity.
intensity = self.hillshade(elevation, vert_exag, dx, dy, fraction)
intensity = intensity[..., np.newaxis]
# Blend the hillshade and rgb data using the specified mode
lookup = {
'hsv': self.blend_hsv,
'soft': self.blend_soft_light,
'overlay': self.blend_overlay,
}
if blend_mode in lookup:
blend = lookup[blend_mode](rgb, intensity, **kwargs)
else:
try:
blend = blend_mode(rgb, intensity, **kwargs)
except TypeError as err:
raise ValueError('"blend_mode" must be callable or one of {}'
.format(lookup.keys)) from err
# Only apply result where hillshade intensity isn't masked
if np.ma.is_masked(intensity):
mask = intensity.mask[..., 0]
for i in range(3):
blend[..., i][mask] = rgb[..., i][mask]
return blend
[docs] def blend_hsv(self, rgb, intensity, hsv_max_sat=None, hsv_max_val=None,
hsv_min_val=None, hsv_min_sat=None):
"""
Take the input data array, convert to HSV values in the given colormap,
then adjust those color values to give the impression of a shaded
relief map with a specified light source. RGBA values are returned,
which can then be used to plot the shaded image with imshow.
The color of the resulting image will be darkened by moving the (s, v)
values (in hsv colorspace) toward (hsv_min_sat, hsv_min_val) in the
shaded regions, or lightened by sliding (s, v) toward (hsv_max_sat,
hsv_max_val) in regions that are illuminated. The default extremes are
chose so that completely shaded points are nearly black (s = 1, v = 0)
and completely illuminated points are nearly white (s = 0, v = 1).
Parameters
----------
rgb : ndarray
An MxNx3 RGB array of floats ranging from 0 to 1 (color image).
intensity : ndarray
An MxNx1 array of floats ranging from 0 to 1 (grayscale image).
hsv_max_sat : number, default: 1
The maximum saturation value that the *intensity* map can shift the
output image to.
hsv_min_sat : number, optional
The minimum saturation value that the *intensity* map can shift the
output image to. Defaults to 0.
hsv_max_val : number, optional
The maximum value ("v" in "hsv") that the *intensity* map can shift
the output image to. Defaults to 1.
hsv_min_val : number, optional
The minimum value ("v" in "hsv") that the *intensity* map can shift
the output image to. Defaults to 0.
Returns
-------
ndarray
An MxNx3 RGB array representing the combined images.
"""
# Backward compatibility...
if hsv_max_sat is None:
hsv_max_sat = self.hsv_max_sat
if hsv_max_val is None:
hsv_max_val = self.hsv_max_val
if hsv_min_sat is None:
hsv_min_sat = self.hsv_min_sat
if hsv_min_val is None:
hsv_min_val = self.hsv_min_val
# Expects a 2D intensity array scaled between -1 to 1...
intensity = intensity[..., 0]
intensity = 2 * intensity - 1
# Convert to rgb, then rgb to hsv
hsv = rgb_to_hsv(rgb[:, :, 0:3])
hue, sat, val = np.moveaxis(hsv, -1, 0)
# Modify hsv values (in place) to simulate illumination.
# putmask(A, mask, B) <=> A[mask] = B[mask]
np.putmask(sat, (np.abs(sat) > 1.e-10) & (intensity > 0),
(1 - intensity) * sat + intensity * hsv_max_sat)
np.putmask(sat, (np.abs(sat) > 1.e-10) & (intensity < 0),
(1 + intensity) * sat - intensity * hsv_min_sat)
np.putmask(val, intensity > 0,
(1 - intensity) * val + intensity * hsv_max_val)
np.putmask(val, intensity < 0,
(1 + intensity) * val - intensity * hsv_min_val)
np.clip(hsv[:, :, 1:], 0, 1, out=hsv[:, :, 1:])
# Convert modified hsv back to rgb.
return hsv_to_rgb(hsv)
[docs] def blend_soft_light(self, rgb, intensity):
"""
Combine an rgb image with an intensity map using "soft light" blending,
using the "pegtop" formula.
Parameters
----------
rgb : ndarray
An MxNx3 RGB array of floats ranging from 0 to 1 (color image).
intensity : ndarray
An MxNx1 array of floats ranging from 0 to 1 (grayscale image).
Returns
-------
ndarray
An MxNx3 RGB array representing the combined images.
"""
return 2 * intensity * rgb + (1 - 2 * intensity) * rgb**2
[docs] def blend_overlay(self, rgb, intensity):
"""
Combines an rgb image with an intensity map using "overlay" blending.
Parameters
----------
rgb : ndarray
An MxNx3 RGB array of floats ranging from 0 to 1 (color image).
intensity : ndarray
An MxNx1 array of floats ranging from 0 to 1 (grayscale image).
Returns
-------
ndarray
An MxNx3 RGB array representing the combined images.
"""
low = 2 * intensity * rgb
high = 1 - 2 * (1 - intensity) * (1 - rgb)
return np.where(rgb <= 0.5, low, high)
[docs]def from_levels_and_colors(levels, colors, extend='neither'):
"""
A helper routine to generate a cmap and a norm instance which
behave similar to contourf's levels and colors arguments.
Parameters
----------
levels : sequence of numbers
The quantization levels used to construct the `BoundaryNorm`.
Value ``v`` is quantized to level ``i`` if ``lev[i] <= v < lev[i+1]``.
colors : sequence of colors
The fill color to use for each level. If *extend* is "neither" there
must be ``n_level - 1`` colors. For an *extend* of "min" or "max" add
one extra color, and for an *extend* of "both" add two colors.
extend : {'neither', 'min', 'max', 'both'}, optional
The behaviour when a value falls out of range of the given levels.
See `~.Axes.contourf` for details.
Returns
-------
cmap : `~matplotlib.colors.Normalize`
norm : `~matplotlib.colors.Colormap`
"""
slice_map = {
'both': slice(1, -1),
'min': slice(1, None),
'max': slice(0, -1),
'neither': slice(0, None),
}
_api.check_in_list(slice_map, extend=extend)
color_slice = slice_map[extend]
n_data_colors = len(levels) - 1
n_expected = n_data_colors + color_slice.start - (color_slice.stop or 0)
if len(colors) != n_expected:
raise ValueError(
f'With extend == {extend!r} and {len(levels)} levels, '
f'expected {n_expected} colors, but got {len(colors)}')
cmap = ListedColormap(colors[color_slice], N=n_data_colors)
if extend in ['min', 'both']:
cmap.set_under(colors[0])
else:
cmap.set_under('none')
if extend in ['max', 'both']:
cmap.set_over(colors[-1])
else:
cmap.set_over('none')
cmap.colorbar_extend = extend
norm = BoundaryNorm(levels, ncolors=n_data_colors)
return cmap, norm
