Gray(scale) image with a colormap - how to turn into double?

Question

John Kau 2015-7-30

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https://ww2.mathworks.cn/matlabcentral/answers/231845-gray-scale-image-with-a-colormap-how-to-turn-into-double

评论： MatlabEnthusiast 2019-12-22

10.bmp

Hi,

I have an 8-bit image that consists only of gray colors. On checking the characteristics of the image in Matlab with imfinfo, it turns out that it is ColorType "indexed" and has a colormap of 256x3. I would like to transform this image into a simple grayscale image of a n x m matrix (according to its size) class double.

The function ind2gray demands a colormap and using the colormap of this image didn't work on my end. Probably I'm doing something wrong.

Any help is much appreciated.

I'm struggling finding a solution.

Thanks

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Answer 1

David Young 2015-7-30

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https://ww2.mathworks.cn/matlabcentral/answers/231845-gray-scale-image-with-a-colormap-how-to-turn-into-double#answer_187778

编辑：David Young 2015-7-30

在 MATLAB Online 中打开

This works OK:

[imInd, cmap] = imread('10.bmp');
imGrayUint8 = ind2gray(imInd, cmap);
imGrayDouble = im2double(imGrayUint8);
imshow(imGrayDouble);

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Image Analyst 2015-7-31

What did you do when you said "The function ind2gray demands a colormap and using the colormap of this image didn't work on my end"? Because that is exactly what David did. And casting to double shouldn't really be necessary.

MatlabEnthusiast 2019-12-22