[x264-devel] Re: Integral projection

[Loren Merritt]

On Wed, 17 May 2006, Florian Seitner wrote:

> I guessed so. I am currently working on H.264 encoder for an embedded
> chip. The available resources (memory/cache sizes/..) are quite limited
> and an extra computation of an integral image for each frame quite
> costly.
>
> Maybe integral projections for fast block matching would be a good
> feature to add in x264. They are probably quite useable in embedded
> solutions since they are updated locally and do not require as much
> memory as e.g. a whole integral images. In case that there is enough
> memory available to compute the integral images, we could also use them
> for computing the integral projections... .

The integral image was a fun feature that I implemented just because I 
could. It's not useful, and I recommend that you not port it to your 
embedded app even if you could. Even with the integral optimizations, 
exhaustive search is still much slower than any of x264's 3 iterative 
search methods, and rarely produces measurably better motion vectors.

As far as I can tell from a little reading, integral projections are the 
same idea as integral image, applied to PHODS instead of exhaustive 
search. Yes it will be fast, but I have doubts about the quality. PHODS 
didn't work very well in libavcodec.

--Loren Merritt

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