Why do I get iradon error saying THETA does not match the number of projections?

I want to do filter back projection after creating a sinogram, but I keep getting this error: The sinogram is made of 400 projections and has a size of 400 x 500.

Error using iradon>parse_inputs

THETA does not match the number of projections.

Error in iradon (line 119)

[p,theta,filter,d,interp,N] = parse_inputs(args{:});

reconstructed_image = iradon(sinogram, theta)

%This is the part of my code that does not work.

% Display the sinogram

figure;

imshow(sinogram, []);

% Define the angular range (theta) for equally spaced angles from 0 to 180 degrees with a step size of 0.45

theta = 0:0.45:180-0.45;

% Perform filtered back projection (FBP) using iradon to reconstruct the image

reconstructed_image = iradon(sinogram, theta;

% Display the reconstructed image

figure;

imshow(reconstructed_image, []);

Answer 1

[R]

Hi Tevin,

I understand that the projection data i.e. 'sinogram' is made up of 400x500 projections. Therefore, 'theta' value should be a 1x500 numeric vector. The following code demonstrates the changes you can make to resolve the error:

theta = 0:180/500:180-180/500;

You can also use the following command that automatically sets the incremental angle between projections to 180/size(R,2)

reconstructed_image = iradon(sinogram, []);

Refer to the following documentation for more information:

https://www.mathworks.com/help/images/ref/iradon.html#d126e218710:~:text=theta%20%E2%80%94%20Projection%20angles

Hope this helps!

[Tevin]

Thank you.