lets_plot.geom_imshow

lets_plot.geom_imshow(image_data, cmap=None, *, norm=None, alpha=None, vmin=None, vmax=None, extent=None, compression=None)

Display image specified by ndarray with shape.

  • (M, N) - grey-scale image

  • (M, N, 3) - color RGB image

  • (M, N, 4) - color RGB image with alpha channel

This geom is not as flexible as geom_raster() or geom_tile() but vastly superior in the terms of rendering efficiency.

Parameters
image_datandarray

Specify image type, size and pixel values. Supported array shapes are:

  • (M, N): an image with scalar data. The values are mapped to colors (greys by default) using normalization. See parameters norm, cmap, vmin, vmax.

  • (M, N, 3): an image with RGB values (0-1 float or 0-255 int).

  • (M, N, 4): an image with RGBA values (0-1 float or 0-255 int).

The first two dimensions (M, N) define the rows and columns of the image. Out-of-range values are clipped.

cmapstr, optional

Name of colormap. For example “viridis”, “magma”, “plasma”, “inferno”, or any other colormap which is supported by the Palettable package (https://github.com/jiffyclub/palettable) This parameter is ignored for RGB(A) images.

normbool, default=True

True - luminance values in grey-scale image will be scaled to [0-255] range using a linear scaler. False - disables scaling of luminance values in grey-scale image. This parameter is ignored for RGB(A) images.

alpha: float, optional

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

vmin, vmaxnumber, optional

Define the data range used for luminance normalization in grey-scale images. This parameter is ignored for RGB(A) images or if parameter norm=False.

extentlist of 4 numbers: [left, right, bottom, top], optional

Define image’s bounding box in terms of the “data coordinates”.

  • left, right: coordinates of pixels’ outer edge along the x-axis for pixels in the 1-st and the last column.

  • bottom, top: coordinates of pixels’ outer edge along the y-axis for pixels in the 1-st and the last row.

The default is: [-0.5, ncol-0.5, -0.5, nrow-0.5]

compressionint, optional

The compression level to be used by the zlib module. Values from 0 (no compression) to 9 (highest). Value None means that the zlib module uses the default level of compression (which is generally acceptable).

Returns
LayerSpec

Geom object specification.

Notes

This geom doesn’t understand any aesthetics. It doesn’t support color scales either.

Examples

1import numpy as np
2from lets_plot import *
3LetsPlot.setup_html()
4np.random.seed(42)
5image = np.random.randint(256, size=(64, 64, 4))
6ggplot() + geom_imshow(image)


1import numpy as np
2from lets_plot import *
3LetsPlot.setup_html()
4n = 64
5image = 256 * np.linspace(np.linspace(0, .5, n), \
6                          np.linspace(.5, .5, n), n)
7ggplot() + geom_imshow(image, norm=False)


1import numpy as np
2from lets_plot import *
3LetsPlot.setup_html()
4np.random.seed(42)
5image = np.random.normal(size=(64, 64))
6ggplot() + geom_imshow(image, vmin=-1, vmax=1)