[libcamera-devel] [PATCH v2 1/6] libcamera: bayer_format: Add a toPixelFormat() helpers to the BayerFormat class

[Naushir Patuck]

Hi Laurent,


On Tue, 26 Oct 2021 at 23:46, Laurent Pinchart <
laurent.pinchart at ideasonboard.com> wrote:

> Hi Naush,
>
> On Tue, Oct 26, 2021 at 11:48:24AM +0100, Naushir Patuck wrote:
> > On Tue, 26 Oct 2021 at 08:48, Naushir Patuck wrote:
> > > On Mon, 25 Oct 2021 at 14:58, Laurent Pinchart wrote:
> > >> On Fri, Oct 22, 2021 at 03:39:02PM +0100, Naushir Patuck wrote:
> > >> > Add a BayerFormat::toPixelFormat() member function to convert a
> BayerFormat to a
> > >> > PixelFormat type. This conversion uses the existing bayerToV4l2
> conversion
> > >> > table.
> > >> >
> > >> > Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> > >> > Reviewed-by: David Plowman <david.plowman at raspberrypi.com>
> > >> > ---
> > >> >  include/libcamera/internal/bayer_format.h |  3 +++
> > >> >  src/libcamera/bayer_format.cpp            | 13 +++++++++++++
> > >> >  2 files changed, 16 insertions(+)
> > >> >
> > >> > diff --git a/include/libcamera/internal/bayer_format.h
> b/include/libcamera/internal/bayer_format.h
> > >> > index 723382d4168d..247a60cf0e36 100644
> > >> > --- a/include/libcamera/internal/bayer_format.h
> > >> > +++ b/include/libcamera/internal/bayer_format.h
> > >> > @@ -10,6 +10,8 @@
> > >> >  #include <stdint.h>
> > >> >  #include <string>
> > >> >
> > >> > +#include <libcamera/pixel_format.h>
> > >> > +
> > >> >  #include "libcamera/internal/v4l2_pixelformat.h"
> > >> >
> > >> >  namespace libcamera {
> > >> > @@ -50,6 +52,7 @@ public:
> > >> >
> > >> >       V4L2PixelFormat toV4L2PixelFormat() const;
> > >> >       static BayerFormat fromV4L2PixelFormat(V4L2PixelFormat
> v4l2Format);
> > >> > +     PixelFormat toPixelFormat() const;
> > >> >       BayerFormat transform(Transform t) const;
> > >> >
> > >> >       Order order;
> > >> > diff --git a/src/libcamera/bayer_format.cpp
> b/src/libcamera/bayer_format.cpp
> > >> > index 11355f144f66..c662ba36604c 100644
> > >> > --- a/src/libcamera/bayer_format.cpp
> > >> > +++ b/src/libcamera/bayer_format.cpp
> > >> > @@ -269,6 +269,19 @@ BayerFormat
> BayerFormat::fromV4L2PixelFormat(V4L2PixelFormat v4l2Format)
> > >> >       return BayerFormat();
> > >> >  }
> > >> >
> > >> > +/**
> > >> > + * \brief Convert a BayerFormat into the corresponding PixelFormat
> > >> > + * \return The PixelFormat corresponding to this BayerFormat
> > >> > + */
> > >> > +PixelFormat BayerFormat::toPixelFormat() const
> > >> > +{
> > >> > +     const auto it = bayerToV4l2.find(*this);
> > >> > +     if (it != bayerToV4l2.end())
> > >> > +             return PixelFormat(it->second);
> > >>
> > >> Should we store the PixelFormat in the bayerToV4l2 map to avoid a
> double
> > >> looking (one here, one in the PixelFormat constructor) ? The map
> should
> > >> be renamed to bayerToFormat, and be stored as either
> > >>
> > >> std::map<BayerFormat, std::pair<PixelFormat, V4L2PixelFormat>,
> > >> BayerFormatComparator>
> > >>
> > >> or
> > >>
> > >> struct Formats {
> > >>         PixelFormat pixelFormat;
> > >>         V4L2PixelFormat v4l2Format;
> > >> };
> > >>
> > >> std::map<BayerFormat, Formats, BayerFormatComparator>
> > >
> > > This seems reasonable.  I will update the table with a std::pair for
> 2-way
> > > conversion.
> >
> > Unfortunately this has hit an unexpected complication. DRM formats, and
> subsequently
> > PixelFormat types do not define Mono Bayer formats. The corresponding
> mbus codes
> > are MEDIA_BUS_FMT_Y8_1X8 and MEDIA_BUS_FMT_Y10_1X10.
>
> DRM and V4L2 define greyscale formats (only 8-bit for DRM with
> DRM_FORMAT_R8, 10- and 12-bit formats could be easily added, and
> V4L2_PIX_FMT_GREY, V4L2_PIX_FMT_Y10 and V4L2_PIX_FMT_Y12 for V4L2).
> They're not Bayer formats indeed, because Bayer filters are only for
> colour formats.
>

I did sport the DRM_FORMAT_R8, but the comment of "/* 8 bpp Red */" make me
think it was not entirely correct to use that for mono sensors.  However, I
am happy to do
so now that you have suggested it :-)


>
> On a side note, I think it was a historical mistake in V4L2 to add Bayer
> formats, we should have defined RAW8/10/12/14/16 formats with the CFA
> pattern being carried out of band.
>
> > Would it be acceptable if the conversion regards these mono BayerFormat
> types as invalid
> > PixelFormat types with a todo to add appropriate support in the future?
> Mono sensor support
> > is still usable as we go from mbus code -> V4L2 4CC correctly, but the
> application can never
> > request a mono output - which it can't do today anyway!
>
> For 8-bit I think you can simply use formats::R8. For 10- and 12-bit,
> would
> https://git.libcamera.org/libcamera/pinchartl/libcamera.git/log/?h=simple/imx8
> help ?
>

Yes it would! I am happy to cherry-pick commits 26f0ce03 and 940d4df4 that
add R10 and R12 formats
to this series if you like?

Thanks,
Naush


> --
> Regards,
>
> Laurent Pinchart
>
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