Radially plot ROIs on image

2 views (last 30 days)
Russell Chow
Russell Chow on 2 Oct 2021
Commented: Russell Chow on 3 Oct 2021
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.

Accepted Answer

Simon Chan
Simon Chan on 2 Oct 2021
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])
  7 Comments
Image Analyst
Image Analyst on 2 Oct 2021
Edited: Image Analyst on 2 Oct 2021
Yes, the drawrectangle() function (unlike plot() and rectangle()) can return an "roi" object class.
Russell Chow
Russell Chow on 3 Oct 2021
@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?

Sign in to comment.

More Answers (0)

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!