How to create a rectangular mask based on current code for making an elliptical mask

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I have an code that creates an elliptical mask and rotates it to a certain angle:
for k = 0:180/deltaK:180-1 % Loop to Rotate the mask in steps.
if rectMask == 0
% Create circular mask.
x = ones(round(diamMax+0.5),1)*(1:round(diamMax+0.5))-round(diamMax+0.5)/2; % Distance in x-direction to centre.
y = (1:round(diamMax+0.5))'*ones(1,round(diamMax+0.5))-round(diamMax+0.5)/2; % Distance in y-direction to centre.
r = sqrt(x.^2+y.^2); % Absolute distance to centre.
maskMax = double(r <= diamMax/2);
% Create mask to convolve the image with.
maskMin = double(abs(x) <= diamMin/2);
maskMin = imrotate(maskMin, k); % Rotation of the mask.
lMaskMax = length(maskMax);
lMaskMin = length(maskMin);
if round(k/90) ~= k/90
maskMin = maskMin(round((lMaskMin-lMaskMax)/2+1.5):round(lMaskMin-...
(lMaskMin-lMaskMax)/2+0.5), round((lMaskMin-lMaskMax)/2+1.5):...
round(lMaskMin-(lMaskMin-lMaskMax)/2+0.5));
end % if
mask = double(maskMax & maskMin);
else % use rectangular mask
% code for creating rectangular mask
% ...
end % if end
end % end for
I would like to replace the elliptical mask if I choose (that is, I want to have both options available by setting a parameter rectMask), with an rectangular mask of with the same size and rotation. How can I do this based on current code?
My input data here are:
  • diamMax
  • diamMin
  • k
  • rectMask = 1 or 0

Accepted Answer

Matt J
Matt J on 4 Aug 2022
Edited: Matt J on 4 Aug 2022
I don't understand how your current code works, but you might consider modifying the code below, as appropriate:
M=256; N=256; %Image dimensions
diamMax=60; diamMin=40;
k=30;
imshow(getMask('rect',M,N,diamMin,diamMax,k))
imshow(getMask('ellipse',M,N,diamMin,diamMax,k))
function Mask=getMask(shape,M,N,diamMin,diamMax,k)
x=(1:M)-(M+1)/2;
y=(1:N)'-(N+1)/2;
switch shape
case 'ellipse'
Mask=(x/diamMax).^2 + (y./diamMin).^2<=1;
case 'rect'
Mask=max(abs(x)/diamMax,abs(y)/diamMin)<=1;
end
Mask=imrotate(Mask,k);
end
  4 Comments
Matt J
Matt J on 5 Aug 2022
Just divide the diams in half
function Mask=getMask(shape,M,N,diamMin,diamMax,k)
diamMin=diamIn/2;
diamMask=diamMask/2;
...
end

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More Answers (1)

Matt J
Matt J on 4 Aug 2022
Edited: Matt J on 4 Aug 2022
You could also just use poly2mask. This would avoid the overhead of imrotate.
M=256; N=256; %Image dimensions
diamMax=60; diamMin=40;
k=30;
imshow(getMask('rect',M,N,diamMin,diamMax,k))
imshow(getMask('ellipse',M,N,diamMin,diamMax,k))
function Mask=getMask(shape,M,N,diamMin,diamMax,k)
switch shape
case 'ellipse'
p=nsidedpoly(1000);
case 'rect'
p=nsidedpoly(4);
end
p=scale(p,[diamMax,diamMin]);
p=translate( rotate(p,-k) ,[M/2,N/2]);
V=p.Vertices;
Mask=poly2mask(V(:,1),V(:,2), M,N);
end

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