Color axis scaling
v = caxis
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.
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.
Reset the axis scaling back to its default range.
Return the values of the current color limits.
v = caxis
v = -1 1
Load the cape file which contains the image data, X, and the colormap, map, for Cape Cod, Massachusetts.
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]')
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;