How to generate a HS histogram?

My task is to acquire the frequency values of the H and S values of an image. Therefore, I'm trying to generate a HS histogram of an image. However, I looked up numerous sources and they all create the H and S histograms separately. To state my problem more clearly, how do I know the number of time the H and S values occur together as a pair? Can anyone point me to the right direction?

Thanks!

Answer 1

[Image Analyst]

See my demo, attached.

[Joshua Jorel Lee]

Thanks! But I have a question. Are you specifically referring to the "Histogram of All Bands" portion of your code? From what I can tell, it's still getting the histogram of each of the H, S, and V values. What I need is a histogram that relates the H and S values, not their individual histograms.

I'm not sure if I'm making much sense, but what I plan to do is to characterize the color of an image based on those two values (H and S). So I need what my professor calls a HS histogram.

[Image Analyst]

You can create a 2D histogram by scanning the images

for col = 1 : columns
    for row = 1 : rows
        r = scaleFactor1 * h(row, column) + 1; % Arrays start at 1.
        c = scaleFactor2 * s(row, column) + 1;
        hist_hs(r, c) = hist_hs(r, c) + 1;
    end
end

You might also like to look at the color frequency image: http://www.mathworks.com/matlabcentral/fileexchange/28164-color-frequency-image

[Joshua Jorel Lee]

I think that's just what I need. Thanks a lot! I assume that the scaleFactor would assume the maximum value from each of the channels?

[Image Analyst]

h and s are continuous. To get into an array, you have to digitize them. For example h and s goes from 0 to 1. If you want your 2D histogram image hist_hs to be 500 in the h direction and 300 in the s direction, you need to have scaleFactor1 be 500 and scaleFactor2 be 300. Of course you also have to preallocate hist_hs to be zeros(500,300) before the loop starts.

[Joshua Jorel Lee]

How would you handle those 0 valued h and s values?

[Image Analyst]

Just ignore them. What needs to be "handled" about them?

[Joshua Jorel Lee]

Since you're using the h and s values as the locations for the frequency values in the new matrix, if I have a 0 value in my h or s vector, MATLAB won't allow the data to be stored.

Example: h(r,c) = 0 or s(r,c) = 0, then r or c will be 0. If I assign hist_hs(r,c), then MATLAB will throw an error.

[Image Analyst]

Adjust the scale factor and add 1. See my edited comment above.

[Joshua Jorel Lee]

Thanks! I took the liberty of putting an if statement that would make the 0 values into 1 instead. Then I used a surf plot to see the result.