Problem with matrix indexing in for loop
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HI guys
In this code, I am getting problem when I am trying to find index of object . In for loop if I comment out img=img+obj(x_f,y_f) then Index x_f and y_f shows from 1 to 512 but when I remove comment then indexes changed. I don't know how it is happening in for loop. Can anyone please help to sort out problem. I will appreciate your help
obj=zeros(512);
obj(230:250,230:250)=5;
%theta = pi/2*180;
figure;
subplot(2,2,1);
imshow(obj);
drawnow;
N=512;
x=[-N/2:N/2-1];
y=[-N/2:N/2-1];
theta=pi/180;
img=zeros(512);
for i=1:180
x_f=round( x .* cos(theta*i) + y.* sin(theta * i)+256);
y_f=round( y .* cos(theta*i)- x .* sin(theta * i)+256);
img=img+obj(x_f,y_f);
% subplot(2,2,2);
% imshow(img);
% drawnow;
end
回答（3 个）
per isakson
2014-6-29
编辑：per isakson
2014-6-29
Here are some links on debugging in Matlab
BTW:
>> x_f(1:5)
ans =
-4 -3 -2 -1 0
Try
>> dbstop if error
Image Analyst
2014-6-29
1 个投票
x_f and y_f will not change depending on whether the img line is in there or commented out. However the values do go negative and you can't have negative indexes into img. What are you trying to do anyway? Draw sine waves into an image???
5 个评论
Parag
2014-6-29
Image Analyst
2014-6-29
Use imrotate() - that's by far the easiest. If you want to do it manually, use the rotation matrix [cos, -sin, sin, cos] like you learned in math class. Don't do it like you tried. Don't.
Parag
2014-6-29
Parag
2014-6-29
Image Analyst
2014-6-30
I would be surprised if that produced a rotated image in labview.
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2014-6-30
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