# How can assign a color for two member of a matrix?

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Amir Torabi on 7 Jan 2020 at 20:23
Commented: Meg Noah on 16 Jan 2020 at 18:04
Hello everyone.
I have written the below code. The aim of the below code is defining a red color for two bubble 26 and 27(eta(:,:,26) and eta(:,:,27).
I did it for one of them, but i have no idea about the assigning red color for bubble 27.
The eta matrix contain the bubbles 26 and 27.
mag=1;
phi=sum(eta(:,:,:).^2,3);
graymap=1/(max(max(phi-min(min(phi)))))*(phi-min(min(phi)));
% subplot(2,1,1)
%Assiging color for particle-26
cmap(:,:,1)=graymap;
cmap(:,:,2)=imcomplement(eta(:,:,26)).*graymap;
cmap(:,:,3)=imcomplement(eta(:,:,26)).*graymap;
%Display
imagesc(cmap);

Meg Noah on 7 Jan 2020 at 23:08
Edited: Meg Noah on 7 Jan 2020 at 23:09
There are a couple of different ways to do it. But I really like just making a false color composite over making a pseudocolor. The trick for your data is picking a threshold for establishing the region that will be colored - I chose 0.1
clc
close all
clear all
mag=1;
phi=sum(eta(:,:,:).^2,3);
graymap=1/(max(max(phi-min(min(phi)))))*(phi-min(min(phi)));
codedImageG = 255*graymap;
codedImageR = codedImageG;
codedImageB = codedImageG;
% make 27 in red only
codedImageG(eta(:,:,27)>0.1) = 0;
codedImageB(eta(:,:,27)>0.1) = 0;
% make 26 in blue only
codedImageR(eta(:,:,26)>0.1) = 0;
codedImageG(eta(:,:,26)>0.1) = 0;
codedImage = zeros(size(codedImageR,1),size(codedImageR,2),3);
codedImage(:,:,1) = codedImageR;
codedImage(:,:,2) = codedImageG;
codedImage(:,:,3) = codedImageB;
codedImage(codedImage > 255) = 255;
codedImage(codedImage < 0) = 0;
imwrite(uint8(codedImage),'codedImage.png');
x1D = -63.5:63.5;
y1D = -63.5:63.5;
figure('color','white');
image(x1D,y1D,myImage);
axis equal
axis tight
This code produces the following image:
And this is the figure:

Amir Torabi on 8 Jan 2020 at 19:23
Thank for your help. However my aim is that bubble 26-27 and even more numbers, have a same color. For example, each of 26 and 27 have red color. And is there any ways to change the color of graymap into another color?
Meg Noah on 9 Jan 2020 at 1:31

Meg Noah on 9 Jan 2020 at 1:36
So the new constraints are:
• change the background color from grayscale to single tone color scale
• arbitrary set of bubbles to be same color
• a couple of different bubble classes with a set of bubbles to be a particular color
This code lets you define the bubble classes and corresponding bubbles for special classes. There are three special classes in the example but it is flexible and extensible. The bubble assignments to each class are also flexible and extensible. Additional metrics could be implemented to classify bubbles. The background bubble color is also user-defined.
For the example: the background bubbles are light teal-blue. Bubbles 8, 26, and 27 are red. Bubbles 1 and 5 are green. Bubbles 6 and 7 are blue. The code is easy to edit to change background bubble color and to add or remove special bubble classes, change membership (indices of bubbles), and change their color.
clc
close all
clear all
mag=1;
phi=sum(eta(:,:,:).^2,3);
graymap=1/(max(max(phi-min(min(phi)))))*(phi-min(min(phi)));
% most of the image (not special bubbles) will be this color in a grayscale
bkgColor = [0 0.5 1];
% special bubbles
% Color = R G B weights for the bubble class
% Bubbles = index into eta array for highlighted bubbles
highlight(1).Color = [1 0 0]; % type 1 bubbles
highlight(1).Bubbles = [8 26 27];
highlight(2).Color =[0 0.9 0]; % type 2 bubbles
highlight(2).Bubbles = [1 5];
highlight(3).Color =[0 0 1]; % type 3 bubbles
highlight(3).Bubbles = [6 7];
% threshold for determining a bubble region
thresh = 0.1;
[ny,nx] = size(graymap);
nClass = length(highlight);
% mask image for the special bubbles
for iClass = 1:length(highlight)
idxBubble = highlight(iClass).Bubbles;
tmpSpecial = zeros(ny,nx);
for iBubble = 1:length(idxBubble)
tmpSpecial(eta(:,:,idxBubble(iBubble))>thresh) = 1;
end
end
% scale between 0 and 255 for a 8-bit color image
graymap = 255*graymap;
graymap(graymap > 255) = 255;
graymap(graymap < 0) = 0;
% create the 3-band (RGB) image
codedImage = zeros(size(graymap,1),size(graymap,2),3);
for iBand = 1:3
for iClass = 1:length(highlight)
codedImage(:,:,iBand) = codedImage(:,:,iBand) + ...
end
end
codedImage(codedImage > 255) = 255;
codedImage(codedImage < 0) = 0;
imwrite(uint8(codedImage),'codedImage.png');
x1D = -63.5:63.5;
y1D = -63.5:63.5;
figure('color','white');
image(x1D,y1D,myImage);
axis equal
axis tight
The code produces these images: