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Drawing Color Histograms and Color Clouds

version 1.4 (3.74 KB) by

Matlab code to plot color histograms and color clouds

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Editor's Note: This file was selected as MATLAB Central Pick of the Week

Usage: createColorHistograms(im_str)
im_str can be an image file location or a three-dimensional array

There seem to be two confounds in plotting color histograms. One is the obvious one of showing a three-dimensional distribution in two-dimensions. And the other is the perceptual confound of showing actual colors without contextual interactions.

The usual method of plotting histograms separately for each of the three primary color bands is hardly optimal. There's no reason to believe that the peaks of the individual bands correspond to the same triplet of color, and the even the fundamental idea of showing spectral densities with graphs that could just as well be used for any universal triplet is dicey. Why not have the graphs speak to you in the visual language of color when they are supposed to be describing color?

As a starting point I decided to bin the color triplets into bands of 25 gray-scale values in each of the RGB band. That is, each (r,g,b) triplet is truncated as (r*,g*,b*) where each value can only be a multiple of 25 up to a maximum of 255. That gives you a resolution of 11^3 voxels in the entire color space covered by a 24-bit representation. The next step is deciding how to order the bins. Our perception of color difference varies quite a bit from the euclidean distance between two color triplets. It seemed prudent to take brightness out of the mix by normalizing all triplets by the sum of their values, making them (r/(r+g+b), g/(r+g+b), b/(r+g+b)) and then ordering them with (1,0,0) (primary red) as the leftmost point.

You can view some examples here:
http://cns.bu.edu/~gsc/ColorHistograms.html

Comments and Ratings (12)

bhagya

bhagya (view profile)

good work

Larry suarez

Thanksyou

shammy

shammy (view profile)

What are the values in the ans variable indicate?

SHAFIQUL

very nice

JASSEM ENIT

how apply this programm on gray image

Stacy

Stacy (view profile)

Thanks for the code! The histograms came out great!

I was wondering if you might be able to clarify the text output. Given the text below, what do each of the #'s represent?

ans =

0.9874 0.9751 0.9515

ans =

1.8751

Drawing color cloud

ans =

0.9874 0.9751 0.9515

ans =

1.8751

3.3805e+003

(I am looking to make judgements of similarity between color images and thought that this might be of use!)

Thanks!

Ronny Meza

Thanks a lot, very useful

He Zhang

Very heuristical! Like it very much! Kiitos!

Great work,
it is really useful,
Thanks for Sharing...

Joao Henriques

emrah sar1

Updates

1.4

Updated links

1.3

Corrected url location

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MATLAB 7.5 (R2007b)

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