Re: [OctDev] imrotate

[Paul K. <pki...@us...>]

On Feb 13, 2005, at 2:35 PM, Justus Piater wrote:

> I've fixed the problems reported by Todd Neal, and added support for
> rot90(). Note that for "crop" one has to do the cropping after the
> rot90(). Moreover, if the image dimensions are not of equal parity
> (odd width and even height, or vice versa), a +/- 90 degree rotation
> entails interpolation. This implies that rot90() cannot be used for
> such rotations.
>
> The new code is designed to behave smoothly across small increments of
> rotation angle, rot90 or not. The result should be exactly the same,
> whether or not rot90 is used.
>
> Please try out the code (Todd!) and tell me what you think. Once I
> have Todd's approval, this code (imrotate.m and imrotate_Fourier.m)
> should replace the existing version of imrotate in CVS.
>
> There are two test functions, testimrotate and testrot90. Look at
> their code and play with them. The other files are needed by these
> two.
>

I replaced the old version of imrotate with what you sent.

I would appreciate a few simple test cases which do not
rely on a human visual system to determine if the result
is correct.

I tried the following:

	X = rand(30);
	Y = imrotate(imrotate(X,30,'bicubic'),-30,'bicubic');
	norm(X(17+[1:5],17+[1:5])-Y(30+[1:5],30+[1:5]))
	ans = 0.46103

Using a smoother function worked better:

	X = peaks(30);
	Y = imrotate(imrotate(X,30,'bicubic'),-30,'bicubic');
	norm(X(17+[1:5],17+[1:5])-Y(30+[1:5],30+[1:5]))
	ans = 0.0036647

Anyone have any better suggestions?

Thanks,

- Paul