How to concatenate 3 histograms on the same graph in Matlab

问题

I have calculated 3 histograms for an rgb image using imhist function in Matlab, one for each channel. I want to plot these histograms on the same graph, where for instance, the histogram for the first (red) channel stretches on the x axis from 0 to 255, the histogram for the second channel stretches from 256 to 511, and finally the histogram for the third channel stretches from 512 to 767. How can I do this?

回答1:

Assuming uint8 precision, each call to imhist will give you a 256 x 1 vector, and so you can concatenate these together into a single 768 x 1 vector. After, call bar with the histc flag. Assuming you have your image stored in im, do this:

red = imhist(im(:,:,1));
green = imhist(im(:,:,2));
blue = imhist(im(:,:,3));
h = [red; green; blue];
bar(h, 'histc');

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As an example, using the onion.png image that's part of the image processing toolbox:

im = imread('onion.png');

This is what the image looks like:

Using the above code to plot the concatenated histogram produces this graph:

来源：https://stackoverflow.com/questions/30951480/how-to-concatenate-3-histograms-on-the-same-graph-in-matlab