MATLAB: Imtransform had shift the center

imtransformimtranslate

Hi, I had 3 images which size 200*200. I would want to aggregate those image with same center after they have been imtransform. Those 3 images are eye scanning. so let's say there is a optic disc, assume it is a circle and I had it's center coordinate. So for example the first image center is 100,100 (this is perfect),2nd is 101,101(so I had to shift -1,-1 to aggregate the 2nd image with the 1st), the last one is 130,130. However, I had calculate that even the optic disc(the circle) had it own center, the image is not scan properly. Therefore I had to rotate my images. I had a Tform and tried to use imtransform. It look okay after the images transform, and I know the image will have difference size, since the I don't want any information lose. Then I change the image size to 300,300. Since I need to aggregate those 3 images to center 150,150 which is the middle of the images. I had try to use imtranslate, which should be fine. However, everytime I try to aggregate the image, the shifting/center is not correct. Below is the code which I had tried.
for n=1:no_of_pics        
          temp_recover=cell2mat(T(n,1));
          %if it is left eye, it need to be fliped
          if analyzingEye=='OS'
              temp_recover=flipdim(temp_thickness,2);
          end           
          temp_recover(isnan(temp_recover))=0;
          %peaks is the center detected by hough method
          temp_xcenter=ceil(peaks(1,n)*200/668);
          temp_ycenter=ceil(peaks(2,n)*200/668);
          % matrix below is trying to rotate the image about the certain center not the origin
          temp_tocenter=[1 0 0;0 1 0;-(150-temp_xcenter) -(150-temp_ycenter) 1];
          temp_back=[1 0 0;0 1 0;150-temp_xcenter 150-temp_ycenter 1];
          temp_recover=imtransform(temp_recover,maketform('affine',temp_tocenter*cell2mat(TTFORM(n,1))*temp_back),'XData',[1 301],'YData',[1 301]);
end
However by using this method, the center is shifted to somewhere I don't know. Therefore, I had use another code;
for n=1:no_of_pics        
          temp_recover=cell2mat(T(n,1));
          if analyzingEye=='OS'
              temp_recover=flipdim(temp_thickness,2);
          end
          temp_recover(isnan(temp_recover))=0;
          temp_xcenter=ceil(peaks(1,n)*200/668);
          temp_ycenter=ceil(peaks(2,n)*200/668); 
          temp_recover=imtransform(temp_recover,maketform('affine',cell2mat(TTFORM(n,1))));
          %I am trying to expand the matrix to 300*300 so that I can aggregate the center and no information lost
          temp_recover(300,300)=0;       
          temp_recover=imtranslate(temp_recover,[151-temp_xcenter,151-temp_ycenter],'fillvalue',0);
end
It did better, but still the circle is not perfectly match. I am very frustrated on this. Can someone point out where I had done wrong? Thank you very much

Best Answer

Right for anyone have same problem with me. Here is the better solution. Firstly, you create a translation matrix i.e.
 %dx dy are the length that you need to translate
 shift=[1 0 0;0 1 0;dx dy 1]
then you need a matrix to transform to origin
 %so if you want to rotate at point(150,150)
 to_center=[1 0 0;0 1 0;-150 -150 1]
then you need your rotation matrix which is
 %theta is the angle
 rotation=[cosd(theta) -sind(theta) 0;sind(theta) cosd(theta) 0;0 0 1]
then you need to transform back
 back=[1 0 0;0 1 0;150 150 1]
therefore, the overall matrix will be
 final=shift*to_center*rotation*back
hope this can help you :)
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