How to extract the radial profile in 'quarter' of circle?

Hi all,

I got an image which is a quarter of circle, and I want to extract the values in a curved line radially which center is a bottm right of the corner.

Here is the code for the radial profile. I modified a little bit of the radial profile code, which is posted in the Mathwork.

function profile = radialprofile(img)
    [x y] = size(img2)
    Z_integer=round(abs(x+1i*y/radial_step)+1);    
end

How can I consider the fixed center position in the code?

Any suggestion and help is welcome. Thank you in advance. Haein

Answer 1

[Bjorn Gustavsson]

Think of this in cylindrical coordinates:

phi360 = linspace(0,2*pi,361);
r0 = [x_lower_right,y_lower_righth];
r = 12;
r_circ = [r*cos(phi360(:))+r0(1),r*sin(phi360(:))+r0(2)];

So that gives you coordinates on an entire circle;

To calculate the image-profile along a sector of that circle you can use interp2:

Im_sector = interp2(1:size(Im,2),1:size(Im,1),Im,r_circ(90:180,1),r_circ(90:180),'spline');

You might want to adjust any parts of this.

HTH

[Haein Shin]

Thanks! It works well!!

[Bjorn Gustavsson]

You're welcome!

Answer 2

[Simon Chan]

You may extarct the values of the radial profiles from variable 'display_profile' according to the code below.

It is a little bit long but allows you to define each parameter when extracting the profiles.

rawdata = imread('demo.png');                               % Image
[Ny,Nx,Nc] = size(rawdata);
cx = Nx;                                                    % Define center of circle at the bottom right
cy = Ny;                                                    % Define center of circle at the bottom right
theta_start = -pi;                                          % Profile starts at botton left                                     
theta_end = -pi/2;                                          % Profile ends at top right
Nprofile = 200;                                             % Number of radial profiles
theta = linspace(theta_start,theta_end,Nprofile);
rho_start = 1150;                                           % profile start at distance rho_start from circle center
rho_end = min(Nx,Ny);                                       % profile end at distance rho_end from circle center
[x_start,y_start] = pol2cart(theta,repelem(rho_start,1,Nprofile));
xs = x_start + cx;                                  
ys = y_start + cy;
[x_end,y_end] = pol2cart(theta,repelem(rho_end,1,Nprofile));
xe = x_end + cx;
ye = y_end + cy;
Npoint = 100;                                               % Number of points on each radial profile
profile = zeros(Npoint,1,Nc,Nprofile);                      % Pre-allocate variable profile
for k = 1:Nprofile
    profile(:,:,:,k) = improfile(rawdata,[xs(k) xe(k)],[ys(k) ye(k)],Npoint);
end
display_profile = permute(profile,[1 4 3 2]);               % Re-arrange for displayed profile
figure(1)
subplot(1,2,1)
imshow(rawdata);
hold on
title('Image with profile start and end points');
plot(xs,ys,'b.');                                           % Blue dots represent profile start location 
plot(xe,ye,'g.');                                           % Green dots represent profile end location
subplot(1,2,2)
imshow(display_profile);
title('Extracted profiles');