Randomizing Color to 3D Objects - improving speed

Hi all,

I have a 3D array with spheres embedded in the array, labeled as 1, and 0 elsewhere. I want to count the spheres and then randomize color with each sphere so when I look at an arbitrary 2D slice through the 3D array, I can verify that each sphere was uniquely identified. (i.e. if two spheres were close together and were considered the same sphere, they would be the same color). Anyways I've completed the task in a simple manner (see below) and my question pertains to how to make this operation faster. Any and all help will be greatly appreciated. Thank you.

if true
  % code
SphereLabel=bwlabeln(SphereBW,26);
AddMatrix = zeros(512,512,256,'uint8');
hWaitBar=waitbar(0,'Randomizing');
for i = 1:max(SphereLabel(:))
  f1=round(rand(1)*255);
  AddMatrix(SphereLabel==i)=f1;
  waitbar(i/max(X(:)))
end
delete(hWaitBar)
AddMatrix(:,:,:,2) = AddMatrix(:,:,:,1); 
AddMatrix(:,:,:,3) = AddMatrix(:,:,:,1); 

end

If there is a large number of spheres in the matrix, then this will take a long time. I'm not sure if there is a faster way, but I thought I'd ask if anyone had any suggestions to improve the speed of this. Always appreciate it.

Cheers, Edwin

Answer 1

[Image Analyst]

Edwin:

Did you know there's a function called label2rgb(). I think this is what you need.

[Image Analyst]

Regarding your "Answer" about colors being too close to each other, you can make up your own custom map I think. Like you can use the lines() map, or your own one with random colors widely spaced out in color space.

[Edwin]

Ah, yea that would be great! Would you mind elucidating on how to implement that with label2rgb, please? I really appreciate it!

[Image Analyst]

I've only done it with 2D labeled images, but here's a snippet from my Image Segmentation Tutorial:

labeledImage = bwlabel(binaryImage, 8);     % Label each blob so we can make measurements of it
coloredLabels = label2rgb (labeledImage, 'hsv', 'k', 'shuffle'); % pseudo random color labels

subplot(3, 3, 4);
imshow(labeledImage, []);
title('Labeled Image, from bwlabel()');
subplot(3, 3, 5);
imshow(coloredLabels);
caption = sprintf('Pseudo colored labels, from label2rgb().\nBlobs are numbered from top to bottom, then from left to right.');
title(caption);

Answer 2

[Edwin]

Hi,

Thank you for the speedy response. I am aware of the function; my issue with that is that due to the way 'bwlabeln' labels the spheres, neighbors will have RGB values close to each other. Ideally, I would like to have completely random RGB values so neighboring spheres will have unique colors.

Also, I also realized an issue with my code. I would need to do the randomizing for all three RGB values. I.e. would need to be adjusted like:

    % code
for i = 1:max(SphereLabel(:))
  f1=round(rand(1)*255);
  f1=round(rand(2)*255);
  f1=round(rand(3)*255);
  AddMatrix1(SphereLabel==i)=f1;
  AddMatrix2(SphereLabel==i)=f2;
  AddMatrix3(SphereLabel==i)=f3;
  waitbar(i/max(X(:)))
end
delete(hWaitBar)
RGBMatrix(:,:,1,:) = AddMatrix1; 
RGBMatrix(:,:,2,:) = AddMatrix2; 
RGBMatrix(:,:,3,:) = AddMatrix3;

I realize I'm asking a pretty unique question here. I'm just eager to learn in hopes to increase my knowledge within matlab. Thank you for any and all help.