MATLAB: Is image scaled down when I use FITGEOTRANS with an affine transformation

fitgeotransMATLAB

I am using FITGEOTRANS to warp an image.
My control points have a range: -1 .. 1, and my moving points have a range -10 .. 10. the image I obtain has a scaling that is off by a factor of 10.
Why is that so? By definition, an affine transform only includes a translation and rotation, no shear and no scaling.

Best Answer

Affine does indeed imply scaling as well. The definition and conventions for different transforms used in MATLAB can be found here:
https://in.mathworks.com/help/images/ref/imregister.html
Under "Definitions" in the table: "Affine transformation consisting of translation, rotation, scale, and shear."
In your case, there is a scaling of 100 between the Moving Points and the Fixed Points.
The reason your image was reduce to 3 pixels was because your original images was 256x256, and the affine transform had both translation, rotation, but also a scaling of 1/100, this reducing the image to 2,56 , i.e. 3 pixels.
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