Manually written tform (images.ge​otrans.Pol​ynomialTra​nsformatio​n2D) does not work in right way.

I am correcting a chromatic errror from two images by using polynomial fitting.

The images have many spot pairs and I could get the images.geotrans.PolynomialTransformation2D object and correct the second image like below.

tform = fitgeotrans(movingPoints,fixedPoints,'polynomial',2);
Jregistered = imwarp(J,tform,'OutputView',imref2d(size(I)));
figure
subplot(1,2,1)
imshowpair(I,J,'falsecolor')
title('compare I & J');
subplot(1,2,2)
imshowpair(I,Jregistered,'falsecolor');
title('after imwarp');

I want to make the tform (images.geotrans.PolynomialTransformation2D) with known coefficients and repeat this procedure.

I made one reusing the coefficients from fitgeotrans, but it makes totally different images.

tform_new = images.geotrans.PolynomialTransformation2D(tform.A,tform.B) ;
J_new= imwarp(J,imref2d(size(J)),tform_new,'OutputView',imref2d(size(I)));

figure
subplot(1,2,1)
imshowpair(I,J,'falsecolor')
title('compare I & J');
subplot(1,2,2)
imshowpair(I,J_new,'falsecolor');
title('after imwarp');

The 'tform' and 'tform_new' are exactly same as shown in worksapce.

I do not understand what makes this difference. I need to edit the coefficients.

Is there any hidden parameter or property in 'images.geotrans.PolynomialTransformation2D' I need to change?

[锐]

Hi, did you solve this question?

Answer 1

[RogerWilco]

Just take into account the coefficient isn't enough to get an exact copy of the transform.

Eventhough the coefficients are the same:

>> isequal(tform.A, tform_new.A)

ans =

logical

1

>> isequal(tform.B, tform_new.B)

ans =

logical

1

The transformations aren't:

>> isequal(tform, tform_new)

ans =

logical

0

In addition to the coefficients PolynomialTransformation2D uses the private properties normTransformXY and normTransformUV, which you can't see/access directly. These aren't set when generating the transformation just by coefficients.

But you can use the hidden methods saveobj and loadobj to rebuild the transformation like:

tformStruct = tform.saveobj;

tform_new = images.geotrans.PolynomialTransformation2D.loadobj(tformStruct);

Now, the transformations are the same:

>> isequal(tform, tform_new)

ans =

logical

1

Hope, this still helps.

Cheers,

Ralf

[Myunghyun]

Thank you for answering this old question, RogerWilco!

[Myunghyun]

Sorry, I cannot accept the answer because I lost the access for MATLAB account I had in the former institute...