Shift the origin (0,0) of the pixels in my image

Question

Aude Rapet 2017-2-1

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回答： wenjie liu 2019-12-5

Hi,

As an input of my code, I need to have some positions on my picture: the positions are in pixels and the origin (0,0) is in the CORNER top left of my picture

The problem is that when I run my code which maps the positions on my picture, the origin shifts to the bottom left :

So my question is : how could I also shift my input (positions of my picture1) so that it is relevant with the code process?

Thank you for your help, Aude

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Answer 1

Walter Roberson 2017-2-1

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set(gca, 'ydir', 'reverse')

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Image Analyst 2017-2-2

编辑：Image Analyst 2017-2-2

No. Just put his line of code, exactly as it is , right after you call imshow(). The badly-named "a" (y values) is not used at all in the call to set().

Aude Rapet 2017-2-2

Thank you Image Analyst for your comment, it is working perfectly!

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Answer 2

Camille Marin 2018-4-13

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编辑：Camille Marin 2018-4-20

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Hello all,

With the same spirit, is it possible to assign specific coordinates to the image's origin in order to use them for an imwarp function ? For instance, I would like to click on my image via the "ginput" function, and I want to assign the X,Y values to the image origin, instead of having it at the top left (1,1).

 close all
 clearvars
 Mire_def= imread ('Couronne_cylindrique_cylindrique_reelle.tif');
 %Declaration of the polynomial (4 degree) vectors A & B. Only A has values, 
 since no modification ocured on the Y axe 
  A_tot=[- 1.5828, 0.8289, 0, 0,0.0007, 0,0,  0, - 1E-06, 0,0,0,0,3E-10,0];
  B=zeros(1,15);
  B(3)=1;
 tform = images.geotrans.PolynomialTransformation2D(A_tot,B);
xWorldLimits = [-121 647];
yWorldLimits = [-528 240];   
RA = imref2d(size(Mire_def),xWorldLimits,yWorldLimits);
   Mire_corr=imwarp(Mire_def,RA,tform)