how to measure the percentage of some colors in image?

I'm going to use the "impixel" function to get the pixel value. now I want to know the percentage of the area that darker than the pixel value I took with the "impixel". which function can I use?

*my image isn't B&W

[Walter Roberson]

When you say "darker" do you mean whose brightness (grayscale intensity) is less than the brightness at the current location?

Or are you looking on a color-plane by color-plane basis, like

(R < current_red) | (G < current_green) | (B < current_blue)

which can include pixels that are brighter in a grayscale sense?

[eran golden]

I'm not sure that I understand your question... what I really want to do is to calculate the percentage of a given pixel-value in the pic:

for example, put your mouse on some point at the pic and want to calculate how much area I have in that pixel-value or darker (yes, as you wrote, "brightness (grayscale intensity) is less than the brightness at the current location"). thanks!

Answer 1

[Image Analyst]

Try something like this (untested)

msgbox('Click on a point');
[x,y] = ginput(1);
row = round(y);
column = round(x);
% Convert to hsv color space
hsvImage = rgb2hsv(rgbImage);
%  Get V of where they clicked:
vRef = hsvImage(row, column, 3);
% Get map of where pixels are darker than ref
mask = hsvImage(:,:,3) < vRef;
% Count the pixels that are darker
numDarkerPixels = sum(mask(:))

[Image Analyst]

By the way, you probably don't want to do what you asked for. You probably want to do color segmentation. You might want to have it try to come up with some number of color classes, like 2 or 3, by using rgb2ind(). Then sum up the number in each class.

Another option would be to use the delta E color difference like I do in my Delta E tutorial in my File Exchange: http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862

[eran golden]

well, i tried your code (delta E) and it seems that all the analisys has been done. but i coudn't figure out how to get the percentage of the color I marked... is this program doing it?

[eran golden]

OK. i tried your code, it seems to be working! here is how i used it:

function [ percent ] = color_percentage( picname )
rgbImage=imread(picname);
imshow(rgbImage);
[x,y] = ginput(1);
row = round(y);
column = round(x);
% Convert to hsv color space
hsvImage = rgb2hsv(rgbImage);
%  Get V of where they clicked:
vRef = hsvImage(row, column, 3);
% Get map of where pixels are darker than ref
mask = hsvImage(:,:,3) < vRef;
% Count the pixels that are darker
numDarkerPixels = sum(mask(:));
hsvImage_size=size(hsvImage);
numofpixels=hsvImage_size(1).*hsvImage_size(2);
percent=numDarkerPixels./numofpixels;
end

it seems that it gives the right claculation. can you take a look at it and see if I did any mistake? I'm new to matlab as you probably notice...

[Image Analyst]

Looks right, though it might be simpler if you did this:

[rows, columns, numberOfColorChannels]  = size(hsvImage);
numberOfPixels = rows * columns;
percent = numDarkerPixels / numberOfPixels;

I still think the number of darker pixels than where they clicked is not as good a method as the delta E method though. Anyway, if you think you have a working solution, can you officially "Accept" this answer?

Answer 2

[Walter Roberson]

Let V be the vector of pixel components you want to test against. Then

Vbright = rgb2gray(reshape(V,1,1,3));
Ibright = rgb2gray(YourImage);
precent_darker = mean(Ibright <= Vbright) * 100;

[eran golden]

instead of 'YourImage' I need to put 'I' [which is 'I=imread(...)'], am I right?

the value of "precent_darker" should give me a number? because it is a matrix...

[Image Analyst]

No. Since "I" is a horrible name for a variable you need to do this:

YourImage = imread(...);

or something similar. I looks too much like l (lower case ell) and 1 (one) and is indistinguishable in some fonts, plus of course too many single letter variables makes your code an alphabet soup that's very hard to follow as compared to using descriptive names.

[eran golden]

I'm sorry, still haven't get what I need. here is my code:

mypic=imread('grains.jpg');
V=impixel(mypic)
Vbright = rgb2gray(reshape(V,1,1,3));
Ibright = rgb2gray(mypic);
precent_darker = mean(Ibright <= Vbright) * 100;

what i need to do next in order to get the percentage of the pixel? the variable 'precent_darker' is a matrix, I want to get a number (=X%) thanks for your kindness :)

[Image Analyst]

Maybe you want to give my code a try then.

Answer 3

[lasmer habiba]

how I can calculate the percentage of color on a mammographic image ???

[Image Analyst]

What do you mean by "color"? Mammograms are x-rays (radiographs) and are gray scale, and so have no "colors" by the usual meaning of "color".

Do you mean the gray scale intensity distribution which you can get from imhist(), histogram(), or histcounts()?

[corona]

Dear Image Analyst

I have some images in red,blue,yellow,green and background is in black (attached). I wish to find out how much is the percentage of each colour in entire image. Kindly advise.

Cheers

corona

[Image Analyst]

Start a new question with this, and say there in that new question (not here)

1. if you know the colors (RGB values) in advance or
2. if you know how many colors there are (four in this image), or
3. if you need to find out how many colors there are.