How do I go about generating a colormap from a matlab file containing RGB values

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Saba Malik 2016-5-13

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https://ww2.mathworks.cn/matlabcentral/answers/284101-how-do-i-go-about-generating-a-colormap-from-a-matlab-file-containing-rgb-values

评论： Walter Roberson 2016-5-16

采纳的回答： Walter Roberson

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Hi all !

I'm really stuck on a problem I would appreciate help with :

I have a matlab file containing 359 variables where each variable consists of a 360 x 3 matrix of double RGB values . For example , variable 1 looks like this :

and so on until row 360 .

My question is how can I go about loading these values into a matrix from which I can generate a colormap?

I have loaded values from a structure into a matrix and represented it as a colormap pretty easily before but my issue here is that I have three RGB values for each row and I don't know how to 'combine' them to get a number which represents a color (if it is even necessary for me to do that).

Many thanks in advance !

Saba

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Answer 1

Walter Roberson 2016-5-13

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https://ww2.mathworks.cn/matlabcentral/answers/284101-how-do-i-go-about-generating-a-colormap-from-a-matlab-file-containing-rgb-values#answer_222052

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cmap = unique(YourArray, 'rows');

or, better,

cmap = uniquetol(YourArray, 1, 'ByRows', true, 'DataScale', 0.004);

cmap is now your colormap.

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Saba Malik 2016-5-14

can i just ask why you specified data scale as 0.004 ? ?

Walter Roberson 2016-5-16

0.004 is slightly less than 1/255. I was aiming to have a change of less than 1/255 be recognized as being the same color.

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Answer 2

Image Analyst 2016-5-13

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https://ww2.mathworks.cn/matlabcentral/answers/284101-how-do-i-go-about-generating-a-colormap-from-a-matlab-file-containing-rgb-values#answer_222042

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Use the colormap() function after you've displayed your grayscale or indexed image

imshow(grayImage);
colormap(variable1); % variable1 is a 360 by 1 colormap matrix.
colorbar; % Show a colored ramp showing what intensities map to what RGB color.

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Saba Malik 2016-5-13

Hi - thanks for your reply

My issue is actually getting to the image stage from the values I have in the matlab file . You said 'display your grayscale image' but I wouldn't be able to do that until I generate a colormap from the RGB values in the file

Image Analyst 2016-5-14

You said you have "a 360 x 3 matrix of double RGB values" - well, that is the exact format that a colormap would take. Is the matrix not a colormap? If no, then what is it?

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