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Dave
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How to get different colours in a matrix with imagesc?

Asked by Dave
on 10 Nov 2018 at 17:55
Latest activity Answered by Dave
on 11 Nov 2018 at 0:57
Hello,
i created a matrix and within the matrix there is a circle of red dots.
i need all the dots to have different colours (red, blue, green) on a random basis, but i dont know how to do it.
here is my code:
m1 = zeros(400,400,3);
center = round(size(m1)/2);
ecc = (rand(1,1000).^0.5).*100;
pol = rand(1,1000).*360;
x = round(cosd(pol) .* ecc); y = round(sind(pol) .* ecc);
m1(sub2ind(size(m1),center(1)-y, center(2)+x)) = 3;
figure; imagesc(m1)
i want to do it with a "for" loop like this
for i = 1:3
ecc = (rand(1,1000).^0.5).*100, i;
pol = rand(1,1000).*360, i;
end
or something like this:
for i = 1:3
ecc = (rand(1,1000, i).^0.5).*100;
pol = rand(1,1000, i).*360;
end
i am very new to matlab and i even fail to figure out where in this code the colour can be placed.
i just know that colour for a very simple matrix works like this:
mat(3,4,1) = 1; %red
mat(5,6,2) = 1; %green
mat(1,2,3) = 1; %blue
thanks for help :)

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2 Answers

Answer by jonas
on 10 Nov 2018 at 20:05
Edited by jonas
on 10 Nov 2018 at 20:06
 Accepted Answer

I made an attempt at fixing your code. What you describe with colors is for RGB images, to display with imshow not imagesc. For imagesc you can simply work with 2D matrices and a suitable colormap.
m1 = zeros(400,400,1);
center = round(size(m1)/2);
ecc = (rand(1,1000).^0.5).*100;
pol = rand(1,1000).*360;
x = round(cosd(pol) .* ecc); y = round(sind(pol) .* ecc);
m1(sub2ind(size(m1),center(1)-y, center(2)+x)) = randi([1 3],1,1000);
figure;
colormap([0 0 0;1 0 0;0 1 0;0 0 1])
imagesc(m1)

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Answer by Dave
on 11 Nov 2018 at 0:57

Thanks a lot for your help Jonas!

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