Customizing colormap for Matlab

Question

I am not sure how to approach this problem. I am trying to find good resources on how to customize a colormap (without using colormap editor) to set your colors and your boundaries for an image in Matlab. I have managed to do it using the colormap editor but I want to figure out how to do it manually.

I am trying to make a colormap that ranges between 0 and 127. The boundaries would be:

0 to 64 is black (0) to white (64)

65 to 127 is blue (65) to red (127)

Can someone give me some advice on how to manually make these changes to the colormap? A good resource would also be useful.

Thanks.

Answer 1

I suggest using linspace. It helps you creating a uniform distribution of numbers in some range.

 blackToWhite = repmat(linspace(0,1,66),3,1)' ; 
 l1 = linspace(0,1,127-65+1);
 blueToRed = [flipud(l1(:)) zeros(size(l1(:))) l1(:) ];

 cmap = [blackToWhite; blueToRed];

The idea is to interpolate [1 0 0] up to [0 0 1]; Each of the color channels, red green and blue is interpolated on its own.

     Red -> 1 ... 0
     Green -> 0 ... 0
     Blue ->  0 ... 1

So I generated l1 both for the red and the blue channel, but flipped it in one of them.