Convert color to value

Hello everyone. I have a jpg image with blue to red color corresponding to different value. There is also a colorbar showing each colorscale correspond to a value. Is there a simple way to convert this color image into matrix? Thanks a lot.

Answer 1

[Jos (10584)]

So you have combinations of red and blue colour values (R,B) that correspond to a some arbitrary single values V according to the colour scale. Perhaps 2D interpolation, will work for you:

Extract all the the (R,B) combinations for each pixel (Rq,Bq)

Vq = interp2(R,B,V,Rq,Bq)

If the green channel is also important, use interp3.

Answer 2

[Image Analyst]

See my attached demo where I used the colormap in a thermal image to convert that into a grayscale temperature image.

Answer 3

[Stephen23]

Use rgb2ind.

[Jos (10584)]

+1 Hopefully it is indeed that simple ...

[Image Analyst]

That's the gist of it, but it's not that simple unless you already have the colormap. In many cases, the user does not and has only some kind of screenshot. My solution also uses rgb2ind() but also does the hard part of figuring out how to obtain the colormap.