[FFmpeg-devel] [PATCH] libavfilter image transformations

[Michael Niedermayer]

On Thu, Apr 22, 2010 at 09:58:02AM -0400, Daniel G. Taylor wrote:
> Hey,
>
> Fixed everything mentioned by Bobby (it is indeed significantly faster to 
> not do the floor/ceil all those times and I added interpolation of edge 
> pixels as suggested), replying to rest here inline.
>
> On 04/20/2010 10:26 PM, Alexander Strange wrote:
>> On Apr 20, 2010, at 5:03 PM, Daniel G. Taylor wrote:
>>
>>> Hey,
>>>
>>> Attached is a patch to add matrix transformation utility methods to 
>>> libavfilter. These are useful for translation, rotation, scaling, etc of 
>>> input pictures and can be easily used from any filter.
>>>
>>> This code was originally part of my work on the deshake/stabilize filter 
>>> and the work of Georg Martius from his transcode transform filter.
>>>
>>> Example usage:
>>>
>>> #include "transform.h"
>>>
>>> ...
>>> double matrix[9];
>>>
>>> avfilter_get_matrix(shift_x, shift_y, radians, scale, (double *)&matrix);
>>> avfilter_transform(src, dst, src_stride, dst_stride, width, 
>>> height,&matrix, INTERPOLATE_BILINEAR, FILL_MIRROR);
>>> ...
>>>
>>> The code supports creating simple matrices from translation, rotation, 
>>> and scaling parameters, adding/subtracting matrices, multiplying a matrix 
>>> by a scalar, and doing the actual picture transform. It supports several 
>>> types of interpolation and edge fill methods.
>>>
>>> This is useful for any filter that might want to transform video frames 
>>> in any way in the future. I have at least one filter that will use this 
>>> but is waiting on motion estimation stuff (deshake/stabilize video).
>>
>> First, are these transforms separable? I'm not familiar with affine 
>> rotations to know how to split them into 1D.

i think they can be implemented through several 1D operations if you
allow sheer operations (that is apply different translation to each line)


>
> I don't know to be honest.
>
>> Second, can they be done in fixed-point?
>
> I believe so, and given some extra time I will try to port it to be e.g. 
> 16.16 fixed point arithmetic.
>
>> Third, can it be merged with swscale? Though that looks hard, filters 
>> should be using it for scaling and transformation if possible.
>
> I'm not at all familiar with swscale and the code looks a bit daunting. I'd 
> rather keep it simple and in libavfilter if possible unless someone is 
> willing to step up and make it all work with swscale!

i agree, about keeping this seperate from swscale currently

also i should probably point out the existence of 
ff_gmc_c()
and
mplayer/libmpcodecs/vf_perspective.c

which do somewhat related things

in that sense allowing libmpcodec filters from mplayer to be used
directly in libavfilter would be great ...

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Avoid a single point of failure, be that a person or equipment.
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