Hi Marek,
On Mon, Jan 16, 2023 at 12:45:34AM +0100, Marek Vasut wrote:
> On 1/15/23 22:32, Laurent Pinchart wrote:
> > On Fri, Jan 13, 2023 at 02:03:33AM +0100, Marek Vasut wrote:
> >> On 1/13/23 00:15, Laurent Pinchart wrote:
> >>> On Tue, Jan 10, 2023 at 08:53:31PM +0100, Marek Vasut wrote:
> >>>> The Cypress EZUSB FX3 UVC example can be configured to report pixel
> >>>> format "e436eb7e-524f-11ce-9f53-0020af0ba770". This is its GUID for
> >>>> BGRA/X 8:8:8:8.
> >>>>
> >>>> The UVC 1.5 spec [1] only defines GUIDs for YUY2, NV12, M420 and I420.
> >>>> This seems to be an extension documented in the Microsoft Windows Media
> >>>> Format SDK[2]. This Media Format SDK defines this GUID as corresponding
> >>>> to `MEDIASUBTYPE_RGB32`.
> >>>>
> >>>> Note that in my case, the FX3 UVC can output either channel order,
> >>>> BGR or RGB or any other mix for that matter. Since Linux commit
> >>>> 1b8dc32286a1a ("[media] uvcvideo: Add GUID for BGR 8:8:8")
> >>>> defined a GUID for `MEDIASUBTYPE_RGB24` channel order as BGR, keep
> >>>> this change consistent and define `MEDIASUBTYPE_RGB32` as BGR as well.
> >>>
> >>> I'd like to see documentation of the MEDIASUBTYPE_RGB32 format that
> >>> indicates the components order precisely. While there's a high chance it
> >>> maps to a BGR (in the V4L2 nomenclature) format, there would still be
> >>> two different options for the A or X component.
> >>
> >> Maybe this ?
> >>
> >> https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src/DirectShow/uncompressed-rgb-video-subtypes.md
> >>
> >> "
> >> Remarks
> >> ...
> >> For RGB 32, every pixel is an RGBQUAD. Each color is one byte, with a
> >> value from 0 to 255, inclusive. The memory layout is:
> >> Byte 0 1 2 3
> >> Value Blue Green Red Alpha or Don't Care
> >> "
> >>
> >> Maps to
> >>
> >> drivers/media/v4l2-core/v4l2-ioctl.c: case V4L2_PIX_FMT_BGR32:
> >> descr = "32-bit BGRA/X 8-8-8-8"; break;
> >
> > Thank you for digging it up. Looks good to me, except that
> > V4L2_PIX_FMT_BGR32 is deprecated (see
> > https://linuxtv.org/downloads/v4l-dvb-apis/userspace-api/v4l/pixfmt-rgb.html#deprecated-rgb-formats).
> > You should use V4L2_PIX_FMT_BGRA32 or V4L2_PIX_FMT_BGRX32 instead.
>
> V4L2_PIX_FMT_XBGR32 , right ?
Yes, my bad. 4CCs are awful :-)
We could also use V4L2_PIX_FMT_ABGR32, but I don't think a UVC camera
would meaningfully produce an alpha channel.
I can change the pixel format when applying the patch if this is fine
with you.
--
Regards,
Laurent Pinchart
