Index in position 1 is invalid. Array indices must be positive integers or logical values?

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Josh Allen
Josh Allen 2018-9-27
评论： Walter Roberson 2023-3-23
I am getting the following error message: Index in position 1 is invalid. Array indices must be positive integers or logical values.
My code is:
clc;
close all;
clear;
% The radon transform of Circle Phantom
PD=phantom('Modified Shepp-Logan');
% pad the image with zeros
padimage = [2,2];
PD= padarray(PD,padimage);
% Original image
subplot(2,3,1)
imagesc(PD);
colormap('gray');
title('Circle Phantom')
xlabel('X')
ylabel('Y')
% Theta is 0:180 with the increment of 0.5 degrees
freq = 2;
thetas = 0:freq:180;
% compute sinogram / radon transformation
gtheta = length(thetas);
gl = size(PD,1);
sinogram = zeros(gl,gtheta);
% loop for the number of angles
for i = 1:length(thetas)
tmpImage = imrotate(PD,-thetas(i),'bilinear','crop');
sinogram(:,i) = sum(tmpImage);
end
subplot(2,3,2)
imagesc(sinogram);
title('Circle Sinogram');
xlabel('l');
ylabel('\theta');
% The inverse radon transform with only 1 back projection that is theta = 0
thetas=0;
Fl = size(sinogram,1);
Ftheta = length(thetas);
% convert thetas to radians
thetas = (pi/180)*thetas;
% set up the backprojected image
g0 = zeros(Fl,Fl);
% find the middle index of the projections
Fmid = ceil(Fl/2);
% set up the coords of the image
[x,y] = meshgrid(ceil(-Fl/2):ceil(Fl/2-1));
% loop over each projection
for i = 1:Ftheta
% Using the back projection formula
rotCoords = Fmid+round(x*sin(thetas(i)) + y*cos(thetas(i)));
% % check which coords are in bounds
% indices = find((rotCoords > 0) & (rotCoords <= Fl));
% newCoords = rotCoords(indices);
% summation
rotCoords=floor(abs(rotCoords));
g0 = g0 + sinogram(rotCoords,i)./Ftheta;
end
subplot(2,3,3);
imagesc(g0);
title('Simple backprojection')
xlabel('X')
ylabel('Y')
The error message is occurring for line 54:
Index in position 1 is invalid. Array indices must be positive integers or logical values.
Error in CT_HW3_BP (line 54)
g0 = g0 + sinogram(rotCoords,i)./Ftheta;
Can anyone tell me what the issue is here?
  3 个评论
显示 1更早的评论
hema
hema 2023-3-23
Index in position 1 is invalid. Array indices must be positive integers or logical values.
A([i,j],:)=A([j,i],:);
my code is:
for i=0:20
for j=0:20
if i==j
A=zeros(i,j);
else
A([i,j],:)=A([j,i],:);
end
please help me

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采纳的回答

Walter Roberson
Walter Roberson 2018-9-27
You have
Fmid = ceil(Fl/2);
[x,y] = meshgrid(ceil(-Fl/2):ceil(Fl/2-1));
rotCoords = Fmid+round(x*sin(thetas(i)) + y*cos(thetas(i)));
when sin(thetas) is 1 then cos(thetas) is 0. so rotCoords would be Fmid + round(x*1 + y*0) which could be as low as ceil(Fl/2) + ceil(-Fl/2) which would be 0. Therefore rotCoords can come out 0, which is not a valid index.
In practice your rotCoords are in the range 0 to 259, where 259 is Fl-1

更多回答（2 个）

Kazi Shakib
Kazi Shakib 2018-10-24
编辑：Walter Roberson 2018-10-24
V=imresize(im,[256,256]);
[m1,n1] = size(V);
blocksize=2;
nob=m1*n1/(blocksize*blocksize);
kk1=0;
for i1=1:(m1/blocksize)
for j1=1:(n1/blocksize)
J=V((blocksize*(1i-1)+1:blocksize*(1i-1)+blocksize),(blocksize*(1j-1)+1:blocksize*(1j-1)+blocksize));
kk1=kk1+(m1/blocksize);
end
end
I have the same probz here..what to do??
William Harris
William Harris 2021-2-5
Hi, I'm getting the same error when I use roi_5, the contents of which are shown below, to index into an image. I'm assuming that the issue is a result of the '10e-09*' at the start. Does anyone know how to deal with this? Or is something else likely to be causing the error?
roi_5 is defined as;
roi_5 = R1rho(22:30, 28:36);
The contents of roi_5:
roi_5 =
1.0e-09 *
0.0313 0.0342 0.0347 0.0307 0.0337 0.0318 0.0355 0.0381 0.0394
0.0329 0.0345 0.0411 0.0412 0.0458 0.0432 0.0456 0.0458 0.0405
0.0383 0.0473 0.0453 0.0393 0.0486 0.0445 0.0455 0.0570 0.0496
0.0415 0.0499 0.0559 0.0541 0.0656 0.0597 0.0627 0.0692 0.0549
0.0457 0.0611 0.0572 0.0508 0.0676 0.0587 0.0636 0.0794 0.0665
0.0491 0.0581 0.0687 0.0650 0.0815 0.0725 0.0811 0.0872 0.0685
0.0638 0.0678 0.0741 0.0655 0.0787 0.0749 0.0777 0.0886 0.0858

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