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caxis

Color axis scaling

Syntax

caxis([cmin cmax])
caxis auto
caxis manual
caxis(caxis)
v = caxis
caxis(axes_handle,...)

Description

caxis controls the mapping of data values to the colormap. It affects any surfaces, patches, and images with indexed CData and CDataMapping set to scaled. It does not affect surfaces, patches, or images with true color CData or with CDataMapping set to direct.

caxis([cmin cmax]) sets the color limits to specified minimum and maximum values. Data values less than cmin or greater than cmax map to cmin and cmax, respectively. Values between cmin and cmax linearly map to the current colormap.

caxis auto computes the color limits automatically using the minimum and maximum data values. This is the default behavior. Color values set to Inf map to the maximum color, and values set to -Inf map to the minimum color. Faces or edges with color values set to NaN are not drawn.

caxis manual and caxis(caxis)freeze the color axis scaling at the current limits. This enables subsequent plots to use the same limits when hold is on.

v = caxis returns a two-element row vector containing the [cmin cmax] currently in use.

caxis(axes_handle,...) uses the axes specified by axes_handle instead of the current axes.

caxis changes the CLim and CLimMode properties of axes graphics objects.

Examples

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Change Color Axis Scaling

Define X, Y, and Z as data for a sphere and view the data as a surface. Define the colors for the surface, C.

[X,Y,Z] = sphere;
C = Z;
surf(X,Y,Z,C)

Values of C are in the range [-1,1]. Values of C near -1 are assigned the lowest values in the colormap. Values of C near 1 are assigned the highest values in the colormap.

Map the top half of the surface to the highest value in the color table by setting the maximum color limit to 0.

caxis([-1,0])

Reset the axis scaling back to its default range.

caxis auto

Return the values of the current color limits.

v = caxis
v =

    -1     1

Set Color Axis Scaling for Image Data

Load the cape file which contains the image data, X, and the colormap, map, for Cape Cod, Massachusetts.

load cape

Display the image with CDataMapping set to scaled, and use the map colormap.

figure
image(X,'CDataMapping','scaled')
colormap(map)

The color limits span the range of the image data, which is 1 to 192. The blue color of the ocean is the first color in the colormap and is mapped to the lowest data value, 1. You can effectively move sea level by changing the lower color limit value using caxis.

Display the image data using four different color limit values.

load cape

figure
colormap(map)

subplot(2,2,1)
image(X,'CDataMapping','scaled')
title('caxis = [1 192]')

subplot(2,2,2)
image(X,'CDataMapping','scaled')
caxis([4,192]) % change caxis
title('caxis = [4 192]')

subplot(2,2,3)
image(X,'CDataMapping','scaled')
caxis([7,192]) % change caxis
title('caxis = [7 192]')

subplot(2,2,4)
image(X,'CDataMapping','scaled')
caxis([10,192]) % change caxis
title('caxis = [10 192]')

More About

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Tips

How Color Axis Scaling Works

Surface, patch, and image graphics objects having indexed CData and CDataMapping set to scaled map CData values to colors in the figure colormap each time they render. CData values equal to or less than cmin map to the first color value in the colormap, and CData values equal to or greater than cmax map to the last color value in the colormap. The following linear transformation is performed on the intermediate values (referred to as C below) to map them to an entry in the colormap (whose length is m, and whose row index is referred to as index below).

index = fix((C-cmin)/(cmax-cmin)*m)+1;
%Clamp values outside the range [1 m]
index(index<1) = 1;
index(index>m) = m; 

See Also

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