Question about rgb image

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Elsie 2014-6-5

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https://ww2.mathworks.cn/matlabcentral/answers/132508-question-about-rgb-image

评论： Image Analyst 2014-6-13

Hi, i have question regarding to imshow a rgb image:

rect =[ ...];
i=image_newC+abs(min(min(image_newC))); % i is a grayscale image
i=imcrop(i,rect);
n = size(unique(reshape(i,size(i,1)*size(i,2),size(i,3))),1);
rgb = ind2rgb(gray2ind(i,n),jet(n));
imshow(rgb,[]); *???why output image is entirely red?*

The purpose is to convert grayscale image to rgb image, i don't know why outcome is not expected. One more thing, is i tried to show it in this way:

imshow(i,[]);
colormap(jet(255));

but i don't know how to access the rgb image if i want to further perform some operations on it. Any way to store it in a variable? Sorry, i am new to Matlab.

Thanks a lot for your help.

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Answer 1

Image Analyst 2014-6-5

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在 MATLAB Online 中打开

Wow! That's about the most complicated, convoluted way of converting a gray scale image to RGB I've ever seen. If image_newC is a unint8 gray scale image, you can simply do

rgbImage = cat(3, image_newC, image_newC, image_newC);

If you want an RGB image with some colormap applied, just as jet(256), do this:

rgbImage = ind2rgb(image_newC, jet(256));

Please see my attached demos if you want to colorize a portion of the image but not the whole image.

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Elsie 2014-6-13

Hi, Image Analyst, is it possible to get the image after colomap? i want the colomapped image...

Image Analyst 2014-6-13

With the demos I posted, you know the color map in advance. You specified it so of course you already know it.

For RGB images there is no color map - it simply does not apply or make sense.

If you want to convert an RGB image to an indexed image, you can use rgb2ind() and it will give you a color map. There is no guarantee that the color map it applies will be anything like the color map you specified when you created the RGB image with ind2rgb().

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