Automatic construction of a colormap around the value zero

Question

I often want to plot a difference image that ranges from some negative number to some positive one. The issue with that is that matlab\'s colormaps scale only from the min

Answer 1

The color mapping can be controlled using the caxis function (which sets the CLim property of the current axes object). The assumption of course is that a scaled color mapping is in use, as opposed to direct color mapping (read the CDataMapping property). By using a zero-centered range as input, you can ensure that zero is always in the middle.

Here is an example:

load penny
P = 4*(P./255) - 1;        %# not centered around zero
imagesc(P), axis image off
colormap(lbmap(64,'BrownBlue')), colorbar

Now we adjust the color mapping to make it symmetric around zero:

c = max(abs([min(P(:)),max(P(:))]));
caxis([-c c])

Note that I am using the Light Bartlein color scheme which was designed as a divergent palette to highlight differences between two extremes.

If the original range is very skewed, you might want to resample the colormap to give it more values in the sub-range that is over-stretched.