How do I get a colormap from JPEG file in MATLAB?

Question

I have a jpg image file of the surface of Neptune. My intention is to build a texture mapping (see Matlab help about this topic). I have used the command imread with the file but jpg files have not a colormap (in general, the command imread produces an MxNx3 matrix and a colormap is a Mx3 matrix). I would like to know how I could do it.

Like an image is more valuable than 1000 words (sometimes), my purpose is doing something like that example but for Neptune.

Answer 1

The MxNx3 array is a RGB array, i.e. at position (x,y), the third dimension corresponds to a triplet of red, green, and blue values.

To change from an RGB image to a indexed image with a colormap, you use the function RGB2IND

[indexedImage,colorMap] = rgb2ind(rgbImage, nColors); %# set nColors to e.g. 128