Calculate image rotation based on old and new positions of two points

Question

I have images of faces in different positions. I want to rotate them, to make the line connecting the eyes always be horizontal. But I don't know how to do this in MATLAB.

And how can I calculate the angle of rotation?

Descriptive drawing of problem:

enter image description here

Automated? Or do you have only a few cases and you can just click on the eyes? — Rody Oldenhuis, Mar 11 '14 at 10:08
I have around.. 200 images. I do the work of manually click on the eyes of all the images, and save this info in a structure. So now, with this info of the position of the eyes, I have to rotate the images, to be all in horizontal. Yes I have processing toolbox ^^ — Shudy, Mar 11 '14 at 10:12

score 3 · Accepted Answer · answered Mar 11 '14 at 10:18

If you already have the locations of the eyes, then it's easy :) Here's an outline:

%//    left eye - right eye
pos = [  30          90    %// X
         80          40];  %// Y 

%// The angle equals the arctangent of dy/dx
angle = atan2(diff(pos(2,:)), diff(pos(1,:)));

%// Rotate in the opposite direction 
img = imrotate(img, -angle);

score 1 · Answer 2 · answered Mar 11 '14 at 13:27

Since you seem to have the Image Processing Toolbox, you can also look into the built-in landmark-based registration functions (especially if your transform is not limited to pure rotation), in particular cpselect with a syntax like:

cpselect(moving,fixed)

And then use fitgeotrans to construct the geometrical transform and imwarp to warp the moving image.

Calculate image rotation based on old and new positions of two points

2 Answers2