# intlut() alternative for LUT consisting of doubles

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Stefan on 15 Aug 2012
Is there a fast alterative to intlut() accepting an array of doubles as LUT?
Problem is, I want to convert grayscale values (uint8) of an image using a LUT consisting of 256 doubles.
Example:
lut = (1:256)+0.1; % upshift by 0.1
A = uint8(randi(256,50));
% current approach
lutMat = repmat(reshape(lut, 1, 1, numel(lut)), ...
size(A));
idx = sub2ind( ...
size(lutMat), ...
repmat((1:size(A, 1))', 1, size(A, 2)), ...
repmat((1:size(A, 2)) , size(A, 1), 1), ...
double(A));
B = lutMat(idx);
The above code works fine, but takes a lot of time and needs too much memory
Image Analyst on 20 Aug 2012
You're still having the problem? Didn't my code do what you want?

Jan on 18 Aug 2012
I'm not sure if I understand the question. Does this help:
B = lut(A);

Image Analyst on 18 Aug 2012
Edited: Image Analyst on 18 Aug 2012
If you're just adding a constant value to the lut-transformed values, like 0.1, you can just do this:
lut = uint8(1:256); % upshift by 0.1
A = uint8(randi(256,50));
B = double(intlut(A, lut)) + 0.1;
If it's not some constant added value, then you can do it like this:
lut = 1000 * rand(256, 1); % A Random reassignment between 0 and 1000.
A = uint8(randi(256,50));
B2 = zeros(size(A), class(lut));
for inputValue = uint8(0) : uint8(255)
indexes = (A == inputValue);
B2(indexes) = lut(inputValue + 1);
end