On Thursday 29 January 2009 09:28:07 Shah, Hardik wrote:
> > -----Original Message-----
> > From: DongSoo Kim [mailto:[email protected]]
> > Sent: Thursday, January 29, 2009 1:14 PM
> > To: Shah, Hardik
> > Cc: [email protected]; [email protected]
> > Subject: Re: [PATCHv2] New V4L2 ioctls for OMAP class of Devices
> >
> > Hello.
> >
> > > +#define VIDIOC_S_COLOR_SPACE_CONV _IOW('V', 83, struct
> >
> > v4l2_color_space_conversion)
> >
> > > +#define VIDIOC_G_COLOR_SPACE_CONV _IOR('V', 84, struct
> >
> > v4l2_color_space_conversion)
> >
> > Do you mind if I ask a question about those ioctls?
> > Because as far as I understand, we can use VIDIOC_S_FMT ioctl to
> > convert colorspaces. Setting through colorspace member in
> > v4l2_pix_format, we could change output colorspace.
> > If there is some different use, can you tell me what it is?
>
> [Shah, Hardik] OMAP Display sub-system supports various pixel formats as
> inputs like YUV, UYVY, RGB24, RGB16 but the compositors which take these
> input format and displays on to the output devices like TV, LCD can only
> understand RGB format. Hardware has provision for converting any data
> taken in YUV or UYVY format to be converted into the RGB formats, before
> giving it to the output devices. To convert this hardware needs to be
> programmed with correct coefficient and offsets to convert from YUV to
> RGB.
Does that mean that when I select a YUV format for output, I still need to
call the color space conversion ioctl? That is not right. Selecting a
format must setup the CSC with decent defaults. I assumed the CSC ioctls
were only meant for fine-grained control: first you call S_FMT to select
the pixelformat which sets up the CSC with defaults, then you call
VIDIOC_G/S_COLOR_SPACE_CONV to modify them if needed.
Regards,
Hans
> These coefficients are pretty standard but still some one may
> require altering it. For this new ioctl is added. Standard equation for
> converting from YUV or UYVY is
>
> | R | | RY RCr RCb | | Y - 16 |
> | G | = 1/K | Gy GCr Gcb | * | Cr - 128 |
> | B | | By BCr BCb | | Cb - 128 |
>
> Where Ry, Rcr, Rcb Gy, Gcr, Gcb, By, Bcr and Bcb are the programmable
> coefficients. But in future offsets like Y-16, Cr-128 or Cb-128 or
> constant like 1/K may also be programmable. So I have added this new
> ioctl.
>
> Regards,
> Hardik Shah
>
> > Regards,
> > Nate
> >
> > --
> > ========================================================
> > Dong Soo, Kim
> > Engineer
> > Mobile S/W Platform Lab. S/W centre
> > Telecommunication R&D Centre
> > Samsung Electronics CO., LTD.
> > e-mail : [email protected]
> > [email protected]
> > ========================================================
>
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--
Hans Verkuil - video4linux developer - sponsored by TANDBERG
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