Re: [PATCH 2/2] v4l2: add new pixel formats supported on dm365

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Guennadi,

On Wednesday 21 December 2011 23:46:24 Guennadi Liakhovetski wrote:
> On Wed, 21 Dec 2011, Laurent Pinchart wrote:
> > On Wednesday 21 December 2011 14:56:36 Hadli, Manjunath wrote:
> > > On Wed, Dec 21, 2011 at 05:32:08, Laurent Pinchart wrote:
> > > > On Friday 16 December 2011 14:42:48 Hadli, Manjunath wrote:
> > > > > On Thu, Dec 15, 2011 at 18:30:47, Laurent Pinchart wrote:
> > > > > > On Thursday 15 December 2011 13:24:58 Manjunath Hadli wrote:
> > > > > > > add new macro V4L2_PIX_FMT_SGRBG10ALAW8 to represent Bayer
> > > > > > > format frames compressed by A-LAW alogorithm.
> > > > > > > add V4L2_PIX_FMT_UV8 to represent storage of C (UV interleved)
> > > > > > > only.
> > > > > > > 
> > > > > > > Signed-off-by: Manjunath Hadli <manjunath.hadli@ti.com>
> > > > > > > Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > > > > > ---
> > > > > > > 
> > > > > > >  include/linux/videodev2.h |    6 ++++++
> > > > > > >  1 files changed, 6 insertions(+), 0 deletions(-)
> > > > > > 
> > > > > > Could you please also document these formats in
> > > > > > Documentation/DocBook/media/v4l ?
> > > > > 
> > > > > I will. Sorry to have missed that out.
> > > > > 
> > > > > > > diff --git a/include/linux/videodev2.h
> > > > > > > b/include/linux/videodev2.h index 4b752d5..969112d 100644
> > > > > > > --- a/include/linux/videodev2.h
> > > > > > > +++ b/include/linux/videodev2.h
> > > > > > > @@ -338,6 +338,9 @@ struct v4l2_pix_format {
> > > > > > > 
> > > > > > >  #define V4L2_PIX_FMT_HM12    v4l2_fourcc('H', 'M', '1', '2')
> > > > > > >  /*  8 YUV
> > > > > > > 
> > > > > > > 4:2:0 16x16 macroblocks */ #define V4L2_PIX_FMT_M420
> > > > > > > v4l2_fourcc('M', '4', '2', '0') /* 12  YUV 4:2:0 2 lines y, 1
> > > > > > > line uv interleaved */
> > > > > > > 
> > > > > > > +/* Chrominance formats */
> > > > > > > +#define V4L2_PIX_FMT_UV8      v4l2_fourcc('U', 'V', '8', ' ')
> > > > > > > /* 8 UV 4:4 */ +
> > > > > > > 
> > > > > > >  /* two planes -- one Y, one Cr + Cb interleaved  */
> > > > > > >  #define V4L2_PIX_FMT_NV12    v4l2_fourcc('N', 'V', '1', '2')
> > > > > > >  /* 12 Y/CbCr
> > > > > > > 
> > > > > > > 4:2:0  */ #define V4L2_PIX_FMT_NV21    v4l2_fourcc('N', 'V',
> > > > > > > '2', '1') /* 12  Y/CrCb 4:2:0  */ @@ -366,6 +369,9 @@ struct
> > > > > > > v4l2_pix_format { #define V4L2_PIX_FMT_SRGGB12
> > > > > > > v4l2_fourcc('R', 'G', '1', '2') /* 12 RGRG.. GBGB.. */ /*
> > > > > > > 10bit raw bayer DPCM compressed to 8 bits */ #define
> > > > > > > V4L2_PIX_FMT_SGRBG10DPCM8 v4l2_fourcc('B', 'D', '1', '0')
> > > > > > > +	/* 10bit raw bayer a-law compressed to 8 bits */ #define
> > > > > > > +V4L2_PIX_FMT_SGRBG10ALAW8 v4l2_fourcc('A', 'L', 'W', '8')
> > > > > > > +
> > > > > > 
> > > > > > That's not very future-proof, how would you describe SGBRG10ALAW8
> > > > > > for instance ?
> > > > > > 
> > > > > > Maybe it's time to standardize FOURCCs for Bayer new formats. We
> > > > > > have 4 characters, we could start with 'B' to denote Bayer,
> > > > > > followed by one character for the order, one for the
> > > > > > compression, and one for the number of bits.
> > > > > 
> > > > > I agree.
> > > > > May be ('B', 'G', 'A', '8') is fine for the above?
> > > > 
> > > > We need to describe at last BGGR, GBRG, GRBG and RGGB. We could use
> > > > 'B', 'g', 'G' and 'R' respectively for the second character. The
> > > > third character would be 'A' for A-law and 'D' for DPCM, and the
> > > > fourth character could describe the bus width in bits from 0 to 15
> > > > with '0' - '9', 'A' - 'F'. However, I suspect that we will need
> > > > 16-bit wide busses for raw Bayer at some point, and a 0 width is
> > > > definitely not useful. We could thus offset the width by some value.
> > > > 
> > > > This is just a preliminary idea, I'm open to suggestions.
> > > 
> > > I think it is a very good suggestion that we can go with.
> > > B : BGGR
> > > g : GBRG
> > > G : GRBG
> > > R : RGGB
> > > 
> > > and 0-F can signify 1-16.
> > 
> > Hans, Guennadi, Sakari, any opinion on that as well ?
> 
> Is there any risk of confusion, if we don't reserve the first character
> for 'B'? I'm just trying to avoid mixed cases, I'm not a great fan of
> those;-)

FOURCCs are not really supposed to be displayed anyway :-)

> What if we use the first two characters for the order like "GR", "GB",...
> AFAICS, 'G' so far only also occurs in GREY and various RGB* / BGR* / ...
> formats, which we wouldn't be confusing with.

Or we could use random FOURCC values as well :-)

There could also be other non-Bayer raw formats, such as panchromatic cells or 
Foveon patterns. I don't know if we need to plan for them already.

> We could further reduce confusion, if we use some other character for A-law
> ('L' or 'W'?)

We could also have µ-law compression, L and W would be ambiguous.

-- 
Regards,

Laurent Pinchart