Radially plot ROIs on image

2021 10 2
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更新时间：2021 10 3
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I have a 64x64 rectangular ROI. I want to place 30 of them in a radial pattern from a set distance from the center of my image. I will then calculate take the FFT of these ROI regions. I can't seem to figure our how to plot the ROIs in a radial pattern. Any starting tips would be greatly appreciated! Let me know if I need to provide more details. Example of what I would like below.

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Simon Chan
Simon Chan 2021-10-2

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Try using function cart2pol, following is an example
clear; clc;
Ny = 1000;
Nx = 1000;
Nz = 30; % Number of ROIs
rho = 200; % Radius, 200 pixels
theta = linspace(-pi,pi,Nz); % Theta separation
cx = 400; % Your center point, x-coordinates = 400 (example)
cy = 700; % Your center point, y-coordinates = 700 (example)
[x,y] = pol2cart(theta,rho); % Use pol2cart
cx_coord = round(cx-x); % Convert back from polar coordinates
cy_coord = round(cy-y);
ROIsize = 64; % Size of ROI
x1 = round(cx_coord - ROIsize/2); % x start position
x2 = x1 + ROIsize - 1; % x end position
y1 = round(cy_coord - ROIsize/2); % y start position
y2 = y1 + ROIsize - 1; % y end position
plot(cx, cy,'g*');
hold on
for k = 1:Nz
plot(cx_coord, cy_coord, 'b.')
plot([x1(k),x2(k),x2(k),x1(k),x1(k)],[y1(k),y1(k),y2(k),y2(k),y1(k)],'r-');
end
xlim([0 Nx])
ylim([0 Ny])

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Russell Chow
Russell Chow 2021-10-2
oh i see. I have never used cart2pol before so i will give it a shot. thank you very much!
Russell Chow
Russell Chow 2021-10-2
@Simon Chan how would I be able to apply an FFT to each of these ROIs and save them in an array?
Russell Chow
Russell Chow 2021-10-2
also is there a way i can use drawrectangle to set the ROIs?
Image Analyst
Image Analyst 2021-10-2
Drawing a rectangle merely draws some graphic in the overlay above the image. It doesn't really "set an ROI". You would need to extract the little image and then call fft2 on it
subImage = grayImage(y1(k) : y2(k), x1(k) : x2(k));
Note that the y's are the first index, not the second.
Russell Chow
Russell Chow 2021-10-2
@Image Analyst thank you! I also used drawrectangle to create the ROIs instead of merely drawing lines.
Image Analyst
Image Analyst 2021-10-2
编辑：Image Analyst 2021-10-2
Yes, the drawrectangle() function (unlike plot() and rectangle()) can return an "roi" object class.
Russell Chow
Russell Chow 2021-10-3
@Image Analyst I have a quick question. i created a mask of the roi and i want to take the FFT of this section, however due to the mask, all my values in the roi are just 1. how can i use the pixel values in the roi without making them binary?

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