Problem using ind2rgb and CDataMapping

Hi, I have a matrix (M) with values ranging from 0 to 5000 that I want to save as an RGB image.

When plotting the image using imagesc(M,'cdatamapping','scaled'); i see exactly what i want.

However, using rgbM=ind2rgb(M,jet); (I tried different sized colormaps, didnt help)

rgbM now has only 2~3 colors and plotting it looks completely different.

I can't find help for this seemingly simple problem online... Any tips on how it should be done?

Answer 1

[Teja Muppirala]

You need to call IND2RGB with a colormap that is as big as your data. Something like this:

M = round(5000*rand(300,300));
imagesc(M,'cdatamapping','scaled');
rgbM = ind2rgb(M - min(M(:)) + 1, jet(range(M(:))+1));

figure;
image(rgbM);

[Syed]

Surprisingly, this doesn't work for 1D images.

x = round(64 * (0.01:0.01:0.99));
figure(1); clf(1);
subplot(211); imagesc(x, 'cdatamapping', 'scaled'); colormap jet;
subplot(212); image(ind2rgb(x - min(x(:)) + 1, jet(range(x(:)) + 1)));

Look at how the spectrum changes in the latter half of the image (the reds):

Answer 2

[Walter Roberson]

I recommend using the File Exchange contribution freezecolors. That will convert your colormapped image into an RGB image; you can then get() the CData of the image as your rgbM array.

[Shay]

Tried freezeColors, it changed the color mapping on the displayed image and the same problem occurs (only shows 2~3 colors).

I should maybe add that i am doing all this in a matlab GUI with 3 axes, not sure if that matters.

Answer 3

[Image Analyst]

Or you can try mat2gray and jet(256)

newImage = mat2gray(oldImage);
imshow(newImage);
colormap(jet(256));