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Axes.pcolor(*args, data=None, **kwargs)

Create a pseudocolor plot of a 2-D array.

Call signatures:

pcolor(C, **kwargs)
pcolor(X, Y, C, **kwargs)

pcolor can be very slow for large arrays; consider using the similar but much faster pcolormesh() instead.


C : array_like

An array of color values.

X, Y : array_like, optional

If given, specify the (x, y) coordinates of the colored quadrilaterals; the quadrilateral for C[i,j] has corners at:

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

Ideally the dimensions of X and Y should be one greater than those of C; if the dimensions are the same, then the last row and column of C will be ignored.

Note that the column index corresponds to the x-coordinate, and the row index corresponds to y; for details, see the Grid Orientation section below.

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

cmap : Colormap, optional, default: None

If None, default to rc settings.

norm : matplotlib.colors.Normalize, optional, default: None

An instance is used to scale luminance data to (0, 1). If None, defaults to normalize().

vmin, vmax : scalar, optional, default: None

vmin and vmax are used in conjunction with norm to normalize luminance data. If either is None, it is autoscaled to the respective min or max of the color array C. If not None, vmin or vmax passed in here override any pre-existing values supplied in the norm instance.

edgecolors : {None, ‘none’, color, color sequence}

If None, the rc setting is used by default. If ‘none’, edges will not be visible. An mpl color or sequence of colors will set the edge color.

alpha : scalar, optional, default: None

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

snap : bool, optional, default: False

Whether to snap the mesh to pixel boundaries.


collection : matplotlib.collections.Collection

Other Parameters:

antialiaseds : bool, optional, default: False

The default antialiaseds is False if the default edgecolors="none" is used. This eliminates artificial lines at patch boundaries, and works regardless of the value of alpha. If edgecolors is not “none”, then the default antialiaseds is taken from rcParams['patch.antialiased'], which defaults to True. Stroking the edges may be preferred if alpha is 1, but will cause artifacts otherwise.

**kwargs :

Any unused keyword arguments are passed along to the PolyCollection constructor:

Property Description
agg_filter unknown
alpha float or None
animated [True | False]
antialiased or antialiaseds Boolean or sequence of booleans
array unknown
clim a length 2 sequence of floats
clip_box a matplotlib.transforms.Bbox instance
clip_on [True | False]
clip_path [ (Path, Transform) | Patch | None ]
cmap a colormap or registered colormap name
color matplotlib color arg or sequence of rgba tuples
contains a callable function
edgecolor or edgecolors matplotlib color spec or sequence of specs
facecolor or facecolors matplotlib color spec or sequence of specs
figure a matplotlib.figure.Figure instance
gid an id string
hatch [ ‘/’ | ‘' | ‘|’ | ‘-‘ | ‘+’ | ‘x’ | ‘o’ | ‘O’ | ‘.’ | ‘*’ ]
label string or anything printable with ‘%s’ conversion.
linestyle or dashes or linestyles [‘solid’ | ‘dashed’, ‘dashdot’, ‘dotted’ | (offset, on-off-dash-seq) | '-' | '--' | '-.' | ':' | 'None' | ' ' | '']
linewidth or linewidths or lw float or sequence of floats
norm unknown
offset_position unknown
offsets float or sequence of floats
path_effects unknown
picker [None|float|boolean|callable]
pickradius unknown
rasterized [True | False | None]
sketch_params unknown
snap unknown
transform Transform instance
url a url string
urls unknown
visible [True | False]
zorder any number

See also

for an explanation of the differences between pcolor and pcolormesh.


X, Y and C may be masked arrays. If either C[i, j], or one of the vertices surrounding C[i,j] (X or Y at [i, j], [i+1, j], [i, j+1], [i+1, j+1]) is masked, nothing is plotted.

The grid orientation follows the MATLAB convention: an array C with shape (nrows, ncolumns) is plotted with the column number as X and the row number as Y, increasing up; hence it is plotted the way the array would be printed, except that the Y axis is reversed. That is, C is taken as C (y, x).

Similarly for meshgrid():

x = np.arange(5)
y = np.arange(3)
X, Y = np.meshgrid(x, y)

is equivalent to:

X = array([[0, 1, 2, 3, 4],
           [0, 1, 2, 3, 4],
           [0, 1, 2, 3, 4]])

Y = array([[0, 0, 0, 0, 0],
           [1, 1, 1, 1, 1],
           [2, 2, 2, 2, 2]])

so if you have:

C = rand(len(x), len(y))

then you need to transpose C:

pcolor(X, Y, C.T)



MATLAB pcolor() always discards the last row and column of C, but Matplotlib displays the last row and column if X and Y are not specified, or if X and Y have one more row and column than C.


In addition to the above described arguments, this function can take a data keyword argument. If such a data argument is given, the following arguments are replaced by data[<arg>]:

  • All positional and all keyword arguments.