assigning color to binary image

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Hassan 2011-12-27

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I have an image consisting of values 1 to 7. I want to show each value with specific color (green,blue,yellow,cyan,magenta,maroon, and sea green). I think I need to use colormap function but dont know how. Any suggestion please?

imshow(BW)
colormap(?)

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Answer 1

Image Analyst 2011-12-27

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Hassan: Then, try this:

% Create sample data
m=7*rand(150);
imshow(m, []);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]); % Maximize figure.
% Construct new colormap with 8 rows and 3 columns
% Each row applies to one gray level.
% Create the 8x3 array any way you want.
% Here I'm using the built-in "jet" array
% set up to go over only 8 gray levels.
cmap = jet(8);
% Apply the colormap
colormap(cmap);
colorbar;

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Image Analyst 2011-12-27

Just take the rgb values and divide by 255, something like

cmap=[0 255 0;... % Green

0 0 255;...

255 255 0;,... % Yellow

... etc.

] / 255;

You can figure out the rgb values for the colors like sea green and maroon by using a program such as Photoshop.

Hassan 2011-12-27

thanks.

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Answer 2

Image Analyst 2011-12-27

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That's not a binary image. It's probably a labeled image, which is a double. Look at this snippet of code that assigns a multitude of different colors to the regions:

% Label each blob with 8-connectivity, so we can make measurements of it
[labeledImage numberOfBlobs] = bwlabel(binaryImage, 8);
% Apply a variety of pseudo-colors to the regions.
coloredLabelsImage = label2rgb (labeledImage, 'hsv', 'k', 'shuffle'); 
% Display the pseudo-colored image.
imshow(coloredLabelsImage);

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Hassan 2011-12-27

thanks for the comment. again, this code doesnt give once color to each label. instead, it gives on color to the connected regions.

Hassan 2011-12-27

Actually Walter's code was the one I needed. the image consists of many regions (connected cells). some regions have value 1, some regions have value 2, ...and some have value 7. Sorry if I didn't describe it clearly.

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Answer 3

Sukuchha 2011-12-27

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first of all if your image is binary, you cant have values from 1 to 7.

if you have image with values 1 to 7, first you have label the connected components.

CC = bwconncomp(BW);
L = labelmatrix(CC);
RGB = label2rgb(L);
figure, imshow(RGB)taken from help file of label2rgb

see doc label2rgb

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Hassan 2011-12-27

thanks Walter. It's the one I needed.

Image Analyst 2011-12-27

Funny, same function as I used, label2rgb. But you're saying now that you don't have a labeled image and that you don't care about labels or connected regions. So that if you had 15 blobs with gray level 4, then all 15 of those should be the same color. And if you had 42 blobs with gray level 5, then all 42 of those should be the same color (but different than the color used for gray level 4). You can do that with just the regular colormap, like my answer below, without having to use label2rgb at all.

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