getting RGB from image created with imagesc

Hi. I am creating am image of a matrix using imagesc.

i want to get the RGB values of every pixel in the image.

I tried using get(im,'CData'), but it gives back the matrix that created the image.

how can do it?

thanks, Ariel

Answer 1

[Mike Garrity]

You probably want ind2rgb. But if you're using imagesc, rather than image, you're probably need to scale your color values. It looks something like this:

v = ??; % my matrix
map = colormap;

minv = min(v(:));
maxv = max(v(:));
ncol = size(map,1);
s = round(1+(ncol-1)*(v-minv)/(maxv-minv));
rgb_image = ind2rgb(s,map);

If you have integer color values, then you don't need to do that scaling before calling ind2rgb.

[ariel]

thanks. However, when I get the RGB data, it is slightly different than what appears on the screen when I use the cursor.

The data is:

0.1250    1.0000    0.8750

while the screen shows this:

Another thing is mapping doubles to RGB - the help of ind2rgb clearly states that this is possible, however when I omitted the rounding of 's' in your example, I got the following error:

Subscript indices must either be real positive integers or logicals.

Error in ind2rgb (line 26)

r = zeros(size(a)); r(:) = cm(a,1);

I'm using Matlab 2015b

Answer 2

[Image Analyst]

imagesc() does not create images - it displays them. So you already have the image. If you want it pseudocolored, look up colormap in the help - there are a variety of predefined colormaps to choose from: hot, winter, jet, parula, etc. Pick one that you like and use ind2rgb to create a pseudocolored RGB image from your gray scale image.

% Use hsv color map to create an RGB image from a gray scale image:
rgbImage = ind2gray(grayImage, hsv(256));

[ariel]

thanks, that was very helpful.

I've noticed that colormap 'jet', for instance, is only 64x3, instead of a "normal" 256 colormap.

does that mean my color resolution is smaller?

[Image Analyst]

Yes. If you want some certain amount, specify it. Like if you want 1000 colors, say jet(1000).