tor 2022-06-02 klockan 14:06 +0200 skrev Paul B Mahol:
> On Thu, Jun 2, 2022 at 1:58 PM Tomas Härdin <tjop...@acc.umu.se>
> wrote:
> >
> > > + uint8_t px[4] = { 0, 0, 0, 255 };
> > > + GetByteContext gb;
> > > + uint8_t *dst;
> > > + uint64_t len;
> > > +
> > > + if (buf_size < 20)
> > > + return AVERROR_INVALIDDATA;
> > > +
> > > + bytestream2_init(&gb, buf, buf_size);
> > > + bytestream2_skip(&gb, 4);
> > > + width = bytestream2_get_be32(&gb);
> > > + height = bytestream2_get_be32(&gb);
> > > + bytestream2_skip(&gb, 2);
> >
> > This should reject linear RGB, not silently treat it as sRGB.
> >
>
> Reject?
From the spec:
> uint8_t colorspace; // 0 = sRGB with linear alpha
> // 1 = all channels linear
RGB in lavc is always sRGB as far as I'm aware.
>
> > > +++ b/libavcodec/qoienc.c
> > >
> > > +static int qoi_encode_frame(AVCodecContext *avctx, AVPacket
> > > *pkt,
> > > + const AVFrame *pict, int
> > > *got_packet)
> > > +{
> > > [...]
> > > + index_pos = QOI_COLOR_HASH(px) & 63;
> > > +
> > > + if (!memcmp(index[index_pos], px, 4)) {
> > > + bytestream_put_byte(&buf, QOI_OP_INDEX |
> > > index_pos);
> >
> > This needs protection against outputting 0x0000000000000001
> >
>
> What?
I had the notion that the encoder could produce runs of index_pos == 0
followed by a single index_pos == 1, thus accidentally signalling end
of image. But the RLE stuff ensures that can't happen. The closest we
can get is an QOI_OP_RGBA with {0,0,0,0} followed by QOI_OP_INDEX with
index_pos == 0 which is five 0x00 in a row. A further match for
index_pos == 0 would be handled as a run. So there's no risk of
accidentally marking end of image. This is why the spec says an encoder
must not output consecutive QOI_OP_INDEX with the same index.
/Tomas
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