Version 3.0.0
matplotlib
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matplotlib.pyplot.imshow

matplotlib.pyplot.imshow(X, cmap=None, norm=None, aspect=None, interpolation=None, alpha=None, vmin=None, vmax=None, origin=None, extent=None, shape=None, filternorm=1, filterrad=4.0, imlim=None, resample=None, url=None, *, data=None, **kwargs)[source]

Display an image, i.e. data on a 2D regular raster.

Parameters:
X : array-like or PIL image

The image data. Supported array shapes are:

  • (M, N): an image with scalar data. The data is visualized using a colormap.
  • (M, N, 3): an image with RGB values (float or uint8).
  • (M, N, 4): an image with RGBA values (float or uint8), i.e. including transparency.

The first two dimensions (M, N) define the rows and columns of the image.

The RGB(A) values should be in the range [0 .. 1] for floats or [0 .. 255] for integers. Out-of-range values will be clipped to these bounds.

cmap : str or Colormap, optional

A Colormap instance or registered colormap name. The colormap maps scalar data to colors. It is ignored for RGB(A) data. Defaults to rcParams["image.cmap"].

aspect : {'equal', 'auto'} or float, optional

Controls the aspect ratio of the axes. The aspect is of particular relevance for images since it may distort the image, i.e. pixel will not be square.

This parameter is a shortcut for explicitly calling Axes.set_aspect. See there for further details.

  • 'equal': Ensures an aspect ratio of 1. Pixels will be square (unless pixel sizes are explicitly made non-square in data coordinates using extent).
  • 'auto': The axes is kept fixed and the aspect is adjusted so that the data fit in the axes. In general, this will result in non-square pixels.

If not given, use rcParams["image.aspect"] (default: 'equal').

interpolation : str, optional

The interpolation method used. If None rcParams["image.interpolation"] is used, which defaults to 'nearest'.

Supported values are 'none', 'nearest', 'bilinear', 'bicubic', 'spline16', 'spline36', 'hanning', 'hamming', 'hermite', 'kaiser', 'quadric', 'catrom', 'gaussian', 'bessel', 'mitchell', 'sinc', 'lanczos'.

If interpolation is 'none', then no interpolation is performed on the Agg, ps and pdf backends. Other backends will fall back to 'nearest'.

See Interpolations for imshow/matshow for an overview of the supported interpolation methods.

Some interpolation methods require an additional radius parameter, which can be set by filterrad. Additionally, the antigrain image resize filter is controlled by the parameter filternorm.

norm : Normalize, optional

If scalar data are used, 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. This parameter is ignored for RGB(A) data.

vmin, vmax : scalar, optional

When using scalar data and no explicit norm, vmin and vmax define the data range that the colormap covers. By default, the colormap covers the complete value range of the supplied data. vmin, vmax are ignored if the norm parameter is used.

alpha : scalar, optional

The alpha blending value, between 0 (transparent) and 1 (opaque). This parameter is ignored for RGBA input data.

origin : {'upper', 'lower'}, optional

Place the [0,0] index of the array in the upper left or lower left corner of the axes. The convention 'upper' is typically used for matrices and images. If not given, rcParams["image.origin"] is used, defaulting to 'upper'.

Note that the vertical axes points upward for 'lower' but downward for 'upper'.

extent : scalars (left, right, bottom, top), optional

The bounding box in data coordinates that the image will fill. The image is stretched individually along x and y to fill the box.

The default extent is determined by the following conditions. Pixels have unit size in data coordinates. Their centers are on integer coordinates, and their center coordinates range from 0 to columns-1 horizontally and from 0 to rows-1 vertically.

Note that the direction of the vertical axis and thus the default values for top and bottom depend on origin:

  • For origin == 'upper' the default is (-0.5, numcols-0.5, numrows-0.5, -0.5).
  • For origin == 'lower' the default is (-0.5, numcols-0.5, -0.5, numrows-0.5).

See the example origin and extent in imshow for a more detailed description.

shape : scalars (columns, rows), optional, default: None

For raw buffer images.

filternorm : bool, optional, default: True

A parameter for the antigrain image resize filter (see the antigrain documentation). If filternorm is set, the filter normalizes integer values and corrects the rounding errors. It doesn't do anything with the source floating point values, it corrects only integers according to the rule of 1.0 which means that any sum of pixel weights must be equal to 1.0. So, the filter function must produce a graph of the proper shape.

filterrad : float > 0, optional, default: 4.0

The filter radius for filters that have a radius parameter, i.e. when interpolation is one of: 'sinc', 'lanczos' or 'blackman'.

resample : bool, optional

When True, use a full resampling method. When False, only resample when the output image is larger than the input image.

url : str, optional

Set the url of the created AxesImage. See Artist.set_url.

Returns:
image : AxesImage
Other Parameters:
**kwargs : Artist properties

These parameters are passed on to the constructor of the AxesImage artist.

See also

matshow
Plot a matrix or an array as an image.

Notes

Unless extent is used, pixel centers will be located at integer coordinates. In other words: the origin will coincide with the center of pixel (0, 0).

There are two common representations for RGB images with an alpha channel:

  • Straight (unassociated) alpha: R, G, and B channels represent the color of the pixel, disregarding its opacity.
  • Premultiplied (associated) alpha: R, G, and B channels represent the color of the pixel, adjusted for its opacity by multiplication.

imshow expects RGB images adopting the straight (unassociated) alpha representation.

Note

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.

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