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

Risposta accettata

Matt J
Matt J il 4 Ago 2022
Modificato: Matt J il 4 Ago 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 Commenti
Happy PhD
Happy PhD il 5 Ago 2022
Modificato: Happy PhD il 5 Ago 2022
Ok, I have reviewed the previous code and i am not getting the same size on the mask of my orginal code.
The mask in my original code is 38x38 pixlar (becuase diamMax, diamMin = 38). The size of the mask in your code is about 72 pixlar and the whole image is case 113 x121. The whole image is larger than the mask.
For some reason the size of the mask itself (which is for k = 0 a circular mask becuase at first I set diamMax and diamMin is equal values) is larger in your code. I can't figure out why.
Matt J
Matt J il 5 Ago 2022
Just divide the diams in half
function Mask=getMask(shape,M,N,diamMin,diamMax,k)
diamMin=diamIn/2;
diamMask=diamMask/2;
...
end

Accedi per commentare.

Più risposte (1)

Matt J
Matt J il 4 Ago 2022
Modificato: Matt J il 4 Ago 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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