[FFmpeg-devel] libavfilter-soc: negate filter artifacts

[Stefano Sabatini]

Hi,

I wonder what's the point of the default offesets assigned in the config_props:
static int config_props(AVFilterLink *link)
{
    NegContext *neg = link->dst->priv;

    avcodec_get_chroma_sub_sample(link->format, &neg->hsub, &neg->vsub);

    switch(link->format) {
    case PIX_FMT_YUVJ444P:
    case PIX_FMT_YUVJ422P:
    case PIX_FMT_YUVJ420P:
    case PIX_FMT_YUVJ440P:
        neg->offY  =
        neg->offUV = 0;
        break;
    default:
        neg->offY  = -4;
        neg->offUV = 1;
    }

    return 0;
}

This is causing artifacts, for example with pixfmt = yuv420p we have:
inrow[j]  = 255
outrow[j] = 255 - inrow[j] + neg->offY =
          = 255 - 255      + -4        = -4 = 251

Simply leaving the offY/UV values to 0 seems to fix the issue in this
case, would be that a valid fix?

Also can someone comment on the usage of the offY / offUV fields?

Regards.
-- 
FFmpeg = Faboulous Free Mortal Peaceful Energized God