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

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

Answer 1

[Walter Roberson]

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

[Aude Rapet]

Thank you Walter for your reply!

I read the documentation about set but I am not quite sure about how to use it. Should I apply it once I have the list of the y- positions? If my y- positions are the 2nd column of a matrix a, should I use it this way :

set(a, 'a(:,2)', 'reverse');

I had the error message : Error using handle.handle/set Invalid or deleted object.

Thank you for your help

[Image Analyst]

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]

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

Answer 2

[Camille Marin]

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)

Answer 3

[wenjie liu]

will you be able to share code on this? I found usage of finding displacement between two images as well. Thank you.