how can I show different values of the image in different colors?

I have a gray scale image with values that differ between 0 and 255. I want to show value 0 as black , value 255 as white, value between 1 to 100 as red, and so on. how can I do that , without changing the image values?

Answer 1

[Massimo Zanetti]

Here it is how to remap a grey scale image into color image by selecting gray values intervals:

%original grayscale image
A=rgb2gray(imread('peppers.png'));
figure; imshow(A);
% 0->black 1:100->red 101-254->green 255->white
cmap = [0,0,0;1,0,0;0,1,0;1,1,1];
%remap original image to indeces 1,2,3,4
B=zeros(size(A));
B(A==0)=1;
B(1<=A & A<=100)=2;
B(101<=A & A<=254)=3;
B(A==255)=4;
%define color image by remapping
RGB = ind2rgb(B,cmap);
%remapped image
figure; imshow(RGB);

[nirit]

Can this be done without changing the pixels value? I want to be able to look at the original values using 'impixelinfo', but at the same time to see colors.

[Massimo Zanetti]

Uh, I got your point. Yes you can do it by direct mapping of the image values into a your custom colormap. Your colormap will be a 256x3 matrix where RAW index 1 to index 256 map the colors of grayscale image values:

A=rgb2gray(imread('peppers.png'));
% 0->black 1:100->red 101-254->green 255->white
cmap=zeros(256,3);
cmap(2:101,:)=repmat([1,0,0],100,1);
cmap(102:255,:)=repmat([0,1,0],154,1);
cmap(end,:)=[1,1,1];
%show
img=imshow(A);
img.CDataMapping='direct';
colormap(cmap);
impixelinfo

In the pixel info string, < xxx > is the value of the gray pixel and [r g b] is the value of the color. :)