MATLAB: Help getting xy coordiantes using for loop and impixel…!

Question

I am trying to get all the z values (x,y coordinates of B image) of certain RGB values. My ultimate goal is to create a big matrix z of all the x and y values that meet the criteria of the if statement. When I run the code, all the z values are shown in the command window, but only the last recorded z value is stored in the work space. I need all the z(x,y coordinates) into one matrix.

A=imread('ulcer.jpg'); % Or any other image is fine

B=imresize(A, [100 100]);

for i=1:100;

 for j=1:100;
x=i;
y=j;
RGB=impixel(B,x,y);
if RGB(1)>= 120 & RGB(1)<=180 & RGB(2)>=20 & RGB(2)<=90 & RGB(3)>=40 & RGB(2)<=100;
  z=[x y]
else
   disp('No');
    end
    end
end

Answer 1

You should take a look at my demo that does this: http://www.mathworks.com/matlabcentral/fileexchange/26420-simplecolordetection

Try it this way instead

% Extract individual color channels.
redChannel = B(:,:,1);
greenChannel = B(:,:,2);
blueChannel = B(:,:,3);
% Create masks to see where criteria is met for each color channel.
redMask = redChannel > 120 & redChannel < 180;
greenMask = greenChannel > 20 & greenChannel < 90;
blueMask = blueChannel >= 40 & blueChannel <= 100;
% Combine to see where criteria is met for all color channels.
overallMask = redMask & greenMask & blueMask;
% Find rows and columns where criteria is met:
[rows, columns] = find(overallMask);