I have an image (256 x 256) where its pixels ranging from 0 to 255. I need to built a look up table to map its values with image pixels.

Since I am a beginner, I cant find a way as how to start with coding for lookuptable. It would really helpful if you would help.

[Florian Bendl]

Please supply an example image and describe what has to be mapped to what. Maybe I can then help.

[Neha W]

I have attached an image explaining the actual thing with simple example. Hope it helps you to understand my problem. Thank you.

Answer 1

[Image Analyst]

Use intlut(). Create your lookuptable, lut, then pass that plus your image into intlut() to get a new, transformed image.

[Neha W]

Thank you for your answer. But do I need to read an image first ?

[Image Analyst]

Yes, you would have to have an image to apply the lut to. But you said you have a 256x256 image already. Just load up the lut and apply it and then show the image.

grayImage = imread('Cameraman.tif');
subplot(2,2,1);
imshow(grayImage);
title('Original Image');
grayLevels = 0:255;
fx = 2*grayLevels+3;
% Make lut
lut = uint8(mod(fx,5));
outputImage = intlut(grayImage, lut);
subplot(2,2,2);
imshow(outputImage);
title('Output Image in range 0-255');
subplot(2,2,3);
imshow(outputImage, []);
title('Output Image Scaled so you can see it');

Of course if you have a formula and operations, then you can just apply those directly like Florian showed, so you wouldn't need a lookup table. Originally you didn't show that formula and intlut() is good for cases where you have some totally general mapping of some gray levels into others.

[Neha W]

Thank you very much. This has really helped me to understand the concept of look up table and to implement it.

Answer 2

[Florian Bendl]

Oh, if I see that correct, then you need no lookup tabel...just do:

im = imread('your file');
% Convert image to double in case it is in some other number format
im = double(im);
% Calculate f(x)
im = 2*im + 3;
% Apply modulo 5
Result = mod( im, 5 )

[Neha W]

Oh. Thank you. It will surely help me a lot. One more thing, if I use different names to assign each step then, would that affect my result?