On Wed, Aug 29, 2018 at 11:50 AM Ezequiel Garcia [off-list ref] wrote:

On Mon, 2018-08-27 at 09:47 +0200, Paul Kocialkowski wrote:

quoted

Hi,

On Wed, 2018-08-22 at 13:59 -0300, Ezequiel Garcia wrote:

quoted

From: Shunqian Zheng <redacted>

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