[FFmpeg-devel] [PATCH] vf_overlay: add support to RGBA packed input and output

[Mark Himsley]

On 30/10/2011 21:47, Michael Niedermayer wrote:
>
> i think we want round to nearest which is
> (x+127)/255
> or
> ((x+127)*257 + 257)>>16
>
> this can be simplified to
> ((x+128)*257)>>16

While I was testing and optimising the code I originally sent on 
2011-03-13 I went through a number of different equations but failed to 
find ((x+128)*257)>>16. The equation I sent was wrong by 1/255th in some 
places, but was a large enough speed-up over (x+127)/255 that in my 
opinion was perceptually close enough.

I am very grateful to you Michael for pointing out ((x+128)*257)>>16.

-- 
Mark