[Libav-user] Help : YUV value for a macroblock in a yuv240p frame

[Boris]

Le mer. 10 avr. 2019 à 11:57, Paul B Mahol <onemda at gmail.com> a écrit :

> On 4/10/19, Boris <ndjoreboris at gmail.com> wrote:
> > Le mar. 9 avr. 2019 à 17:44, Simon Brown <simon.k.brown at gmail.com> a
> écrit
> > :
> >
> >>
> >>> Thanks,
> >>> If I understand what you said, I have to proccess like this :
> >>>
> >>> //Declaration of yuv arrays
> >>> uint16_t yval[mb_height * mb_width][256];
> >>> uint16_t uval[mb_height * mb_width][256];
> >>> uint16_t vval[mb_height * mb_width][256];
> >>>
> >>> for(int mby=0;  mby<mb_height; mby++)
> >>> {
> >>>          for(int mbx=0; mbx <mb_width ;mbx++)
> >>>          {
> >>>              //Now for this 16x16 macroblock
> >>>             for(int y=0; y<16;y++)
> >>>             {
> >>>                for(int x=0; x<16;x++)
> >>>                {
> >>>                  yval[mby*mb_width + mbx][y*16+x] =
> >>> data[0][linesize[0]*y*16+x]; or yval[mby*mb_width + mbx][y*16+x] =
> >>> data[0][y*16+x]???
> >>>                  uval[mby*mb_width + mbx][(y/2)*16+x/2] =
> >>> data[1][linesize[1]*(y/2)*16+x/2];
> >>>                  uval[mby*mb_width + mbx][(y/2)*16+x/2] =
> >>> data[2][linesize[2]*(y/2)*16+x/2];
> >>>                //Setting of Yuv arrays
> >>>
> >>>              }
> >>> }
> >>> //Let's go to  an other macroblock
> >>> }
> >>> }
> >>>
> >>> Regards
> >>>
> >>>>
> >>>> Not quite - the data in data[0] is arranged by pixels, so your
> >> coordinate into that array must include all the pixels, not just the
> >> current macroblock.  So you need:
> >> yval[mby*mb_width + mbx][y*16+x] = data[0][ linesize[0]*(mby*16 + y) +
> >> (mbx*16 + x) ]
> >> so you skip all lines up to the one you're processing, including all
> >> previous macroblocks and all lines already processed in the current
> >> macroblock using "linesize[0]*(mby*16 + y)" and then all the pixels in
> >> the
> >> current line up to the macroblock you're interested in, and any pixels
> >> already processed in that macroblock with "mbx*16 + x".
> >>
> >> I hope that makes sense.
> >>
> >> Regards,
> >> Simon
> >>
> >
> > Hello Simon,
> >
> > I do like you tell me but data[0][ linesize[0]*(mby*16 + y) + (mbx*16 +
> x)
> > ] gives me some negatives pixel's values.
> > Is it normal ?
> > For exemple data[0][ linesize[0]*(mby*16 + y) + (mbx*16 + x) ] =
> >  -62
> > -65
> > -72
> > My question is to know if it is normal to have negatives pixel's value (
> y
> > = -a; u=-b; v=-c) where a, b and c are integers.
>
> Doesn't make sense, post full code.
>

Hello Paul,
The code is the following :
mbx and mby are x,y coordinate (position) of the macroblock in the frame ,
data is AVFrame frame->data and linesize is AVFrame frame->linesize
Then :
 for(int y=0; y<16;y++) //run through the length of the 16x16 macroblock
            {
               for(int x=0; x<16;x++) ////run through the width of the
16x16 macroblock
                {
 cout<<data[0][ linesize[0]*(mby*16 + y) + (mbx*16 + x) ] <<endl;

}
}

So I still getting some negatives values. My question is to know if it's
normal.

Regards

> _______________________________________________
> Libav-user mailing list
> Libav-user at ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/libav-user
>
> To unsubscribe, visit link above, or email
> libav-user-request at ffmpeg.org with subject "unsubscribe".
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://ffmpeg.org/pipermail/libav-user/attachments/20190410/c4236932/attachment.html>