On Wed, Aug 29, 2018 at 11:50 AM Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx> wrote:
>
> On Mon, 2018-08-27 at 09:47 +0200, Paul Kocialkowski wrote:
> > Hi,
> >
> > On Wed, 2018-08-22 at 13:59 -0300, Ezequiel Garcia wrote:
> > > From: Shunqian Zheng <zhengsq@xxxxxxxxxxxxxx>
> > >
> > > Add V4L2_CID_JPEG_LUMA/CHROMA_QUANTIZATION controls to allow userspace
> > > configure the JPEG quantization tables.
> >
> > How about having a single control for quantization?
> >
> > In MPEG-2/H.264/H.265, we have a single control exposed as a structure,
> > which contains the tables for both luma and chroma. In the case of JPEG,
> > it's not that big a deal, but for advanced video formats, it would be
> > too much hassle to have one control per table.
> >
> > In order to keep the interface consistent, I think it'd be best to merge
> > both matrices into a single control.
> >
> > What do you think?
> >
>
> I think it makes a lot of sense. I don't see the benefit in having luma
> and chroma separated, and consistency is good.
>
> I guess the more consistent solution would be to expose a compound
> control, similar to the video quantization one.
>
> struct v4l2_ctrl_jpeg_quantization {
> __u8 luma_quantization_matrix[64];
> __u8 chroma_quantization_matrix[64];
> };
Makes sense indeed. It also lets us avoid the hassle of setting
.min/.max/.dims and other array control stuff, since everything is
already defined by the C struct itself.
Best regards,
Tomasz
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