matplotlib.axes.Axes.pcolormesh¶

Axes.pcolormesh(self, *args, alpha=None, norm=None, cmap=None, vmin=None, vmax=None, shading=None, antialiased=False, data=None, **kwargs)[source]

Create a pseudocolor plot with a non-regular rectangular grid.

Call signature:

pcolormesh([X, Y,] C, **kwargs)


X and Y can be used to specify the corners of the quadrilaterals.

Hint

pcolormesh is similar to pcolor. It is much faster and preferred in most cases. For a detailed discussion on the differences see Differences between pcolor() and pcolormesh().

Parameters:
Carray-like

A scalar 2-D array. The values will be color-mapped.

X, Yarray-like, optional

The coordinates of the corners of quadrilaterals of a pcolormesh:

(X[i+1, j], Y[i+1, j])       (X[i+1, j+1], Y[i+1, j+1])
+-----+
|     |
+-----+
(X[i, j], Y[i, j])       (X[i, j+1], Y[i, j+1])


Note that the column index corresponds to the x-coordinate, and the row index corresponds to y. For details, see the Notes section below.

If shading='flat' the dimensions of X and Y should be one greater than those of C, and the quadrilateral is colored due to the value at C[i, j]. If X, Y and C have equal dimensions, a warning will be raised and the last row and column of C will be ignored.

If shading='nearest' or 'gouraud', the dimensions of X and Y should be the same as those of C (if not, a ValueError will be raised). For 'nearest' the color C[i, j] is centered on (X[i, j], Y[i, j]). For 'gouraud', a smooth interpolation is caried out between the quadrilateral corners.

If X and/or Y are 1-D arrays or column vectors they will be expanded as needed into the appropriate 2-D arrays, making a rectangular grid.

cmapstr or Colormap, default: rcParams["image.cmap"] (default: 'viridis')

A Colormap instance or registered colormap name. The colormap maps the C values to colors.

normNormalize, optional

The Normalize instance scales the data values to the canonical colormap range [0, 1] for mapping to colors. By default, the data range is mapped to the colorbar range using linear scaling.

vmin, vmaxfloat, default: None

The colorbar range. If None, suitable min/max values are automatically chosen by the Normalize instance (defaults to the respective min/max values of C in case of the default linear scaling). It is deprecated to use vmin/vmax when norm is given.

edgecolors{'none', None, 'face', color, color sequence}, optional

The color of the edges. Defaults to 'none'. Possible values:

• 'none' or '': No edge.
• None: rcParams["patch.edgecolor"] (default: 'black') will be used. Note that currently rcParams["patch.force_edgecolor"] (default: False) has to be True for this to work.
• 'face': Use the adjacent face color.
• A color or sequence of colors will set the edge color.

The singular form edgecolor works as an alias.

alphafloat, default: None

The alpha blending value, between 0 (transparent) and 1 (opaque).

The fill style for the quadrilateral; defaults to 'flat' or rcParams["pcolor.shading"] (default: 'flat'). Possible values:

• 'flat': A solid color is used for each quad. The color of the quad (i, j), (i+1, j), (i, j+1), (i+1, j+1) is given by C[i, j]. The dimensions of X and Y should be one greater than those of C; if they are the same as C, then a deprecation warning is raised, and the last row and column of C are dropped.
• 'nearest': Each grid point will have a color centered on it, extending halfway between the adjacent grid centers. The dimensions of X and Y must be the same as C.
• 'gouraud': Each quad will be Gouraud shaded: The color of the corners (i', j') are given by C[i', j']. The color values of the area in between is interpolated from the corner values. The dimensions of X and Y must be the same as C. When Gouraud shading is used, edgecolors is ignored.
• 'auto': Choose 'flat' if dimensions of X and Y are one larger than C. Choose 'nearest' if dimensions are the same.

See pcolormesh grids and shading for more description.

snapbool, default: False

Whether to snap the mesh to pixel boundaries.

Returns:
matplotlib.collections.QuadMesh
Other Parameters:
**kwargs

Additionally, the following arguments are allowed. They are passed along to the QuadMesh constructor:

Property Description
agg_filter a filter function, which takes a (m, n, 3) float array and a dpi value, and returns a (m, n, 3) array
alpha float or None
animated bool
antialiased or aa or antialiaseds bool or list of bools
array ndarray
capstyle {'butt', 'round', 'projecting'}
clim (vmin: float, vmax: float)
clip_box Bbox
clip_on bool
clip_path Patch or (Path, Transform) or None
cmap Colormap or str or None
color color or list of rgba tuples
contains unknown
edgecolor or ec or edgecolors color or list of colors or 'face'
facecolor or facecolors or fc color or list of colors
figure Figure
gid str
hatch {'/', '\', '|', '-', '+', 'x', 'o', 'O', '.', '*'}
in_layout bool
joinstyle {'miter', 'round', 'bevel'}
label object
linestyle or dashes or linestyles or ls str or tuple or list thereof
linewidth or linewidths or lw float or list of floats
norm Normalize or None
offset_position unknown
offsets array-like (N, 2) or (2,)
path_effects AbstractPathEffect
picker None or bool or callable
pickradius unknown
rasterized bool or None
sketch_params (scale: float, length: float, randomness: float)
snap bool or None
transform Transform
url str
urls list of str or None
visible bool
zorder float

pcolor
An alternative implementation with slightly different features. For a detailed discussion on the differences see Differences between pcolor() and pcolormesh().
imshow
If X and Y are each equidistant, imshow can be a faster alternative.

Notes

C may be a masked array. If C[i, j] is masked, the corresponding quadrilateral will be transparent. Masking of X and Y is not supported. Use pcolor if you need this functionality.

Grid orientation

The grid orientation follows the standard matrix convention: An array C with shape (nrows, ncolumns) is plotted with the column number as X and the row number as Y.

Differences between pcolor() and pcolormesh()

Both methods are used to create a pseudocolor plot of a 2-D array using quadrilaterals.

The main difference lies in the created object and internal data handling: While pcolor returns a PolyCollection, pcolormesh returns a QuadMesh. The latter is more specialized for the given purpose and thus is faster. It should almost always be preferred.

There is also a slight difference in the handling of masked arrays. Both pcolor and pcolormesh support masked arrays for C. However, only pcolor supports masked arrays for X and Y. The reason lies in the internal handling of the masked values. pcolor leaves out the respective polygons from the PolyCollection. pcolormesh sets the facecolor of the masked elements to transparent. You can see the difference when using edgecolors. While all edges are drawn irrespective of masking in a QuadMesh, the edge between two adjacent masked quadrilaterals in pcolor is not drawn as the corresponding polygons do not exist in the PolyCollection.

Another difference is the support of Gouraud shading in pcolormesh, which is not available with pcolor.

Note

In addition to the above described arguments, this function can take a data keyword argument. If such a data argument is given, every other argument can also be string s, which is interpreted as data[s] (unless this raises an exception).

Objects passed as data must support item access (data[s]) and membership test (s in data).