Re: [OctDev] imrotate

[Jeffery O. <jj...@cs...>]

Your concernes about a .m implementation of imrotate are wise. However, 
my implementation does not have any loops. It applies the rotation by 
decomposing the rotaion matrix into 3 shears, and then applies the 
shears using Fourier interpolation. As a result, it uses the 1D fft 
function heavily. But since the bulk of those operations are implemented 
efficiently, the speed is OK. I haven't had the chance to run any 
benchmarks yet, but I will soon.

The function uses another function I could submit, called "imshear.m". 
Guess what it does! That's right... applies a shear using Fourier 
interpolation.

Certainly, a C implementation of these functions would be at LEAST 
slightly faster, but I must admit that I'm hesitant because I've never 
written a .oct routine, and I'm not familiar enough with the API to do 
it in a timely manner. Not to mention, I hope I wouldn't have to 
re-implement the fft, etc., myself. Since the vast majority of the data 
manipulation is offloaded to other routines, it might not be worth it.

Since it seems that there are no imrotates lurking around, I guess I 
wouldn't be re-inventing the wheel. I'll spend some time tying up some 
loose ends, and you can check out the "alpha release" once I'm done, if 
you wish.

Jeff

Andy Adler wrote:

>On Fri, 28 Jun 2002, Jeff Orchard wrote:
>
>>I have developed "imrotate.m". I noticed that it is not yet implemented 
>>in the octave collections. Is there one out there that I've simply not 
>>seen? Just want to check before going through the effort of making it 
>>compatible with RGB images, colormaps, etc.
>>
>
>I don't think we have imrotate. It would be a great thing
>to have.
>
>One question: don't you think an *.m file implementation
>would be slow?
>
>I have some C code that does image scaling and
>rotation. (greyscale only) I could contribute that if
>you'd be interested in doing an *oct file implementation.
>
>andy
>_______________________________________
>Andy Adler,
>ad...@nc...
>
>
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