Re: [PATCH 2/3] Document 8-bit and 16-bit YCrCb media bus pixel codes

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi Christian,

On Wednesday 13 July 2011 20:58:12 Christian Gmeiner wrote:
> 2011/7/11 Christian Gmeiner <christian.gmeiner@xxxxxxxxx>:
> > 2011/7/11 Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>:
> >> On Sunday 10 July 2011 20:14:21 Christian Gmeiner wrote:
> >>> Signed-off-by: Christian Gmeiner
> >>> ---
> >>> diff --git a/Documentation/DocBook/media/v4l/subdev-formats.xml
> >>> b/Documentation/DocBook/media/v4l/subdev-formats.xml
> >>> index 49c532e..18e30b0 100644
> >>> --- a/Documentation/DocBook/media/v4l/subdev-formats.xml
> >>> +++ b/Documentation/DocBook/media/v4l/subdev-formats.xml
> >>> @@ -2565,5 +2565,43 @@
> >>>         </tgroup>
> >>>        </table>
> >>>      </section>
> >>> +
> >>> +    <section>
> >>> +      <title>YCrCb Formats</title>
> >>> +
> >>> +      <para>YCbCr represents colors as a combination of three values:
> >>> +      <itemizedlist>
> >>> +       <listitem><para>Y - the luminosity (roughly the
> >>> brightness)</para></listitem>
> >>> +       <listitem><para>Cb - the chrominance of the blue
> >>> primary</para></listitem>
> >>> +       <listitem><para>Cr - the chrominance of the red
> >>> primary</para></listitem>
> >> 
> >> How does that differ from YUV ?
> > 
> > I need to say that I am very new to this whole format stuff and so I
> > am not really sure.
> > In the data sheet
> > http://dxr3.sourceforge.net/download/hardware/ADV7175A_6A.pdf there is
> > on the
> > first page a FUNCTIONAL BLOCK DIAGRAM which shows that there is a
> > "YCrCb to YUV Matrix"
> > stage in the pipeline. I am also fine to use a YUV format for the media
> > bus. Any suggestions?
> 
> Okay I think I have found the difference between YUV and YCrCb - see [1]
> 
> YCbCr 4:2:2
> (Redirected from YUV 4:2:2)
> 
> FourCCs: YUY2, UYVY, YUV2 (Apple Component Video stored in MOV files)
> Samples: http://samples.mplayerhq.hu/V-codecs/YUV2/
> 
> (These FourCC names only reflect that the YCbCr of digital media is
> often falsely mixed up with analog PAL's YUV color space.)
> 
> YCbCr 4:2:2 is a packed YCbCr format in which a pair of consecutive
> pixels is represented by 1 Y sample each but share a Cb sample and a
> Cr sample.
> 
> This type of data may be packaged in a container format with a a
> FourCC of YUY2 which indicates the following byte formatting:
> 
> 
> [1] http://wiki.multimedia.cx/index.php?title=YUV_4:2:2

According to http://en.wikipedia.org/wiki/Yuv,

"Historically, the terms YUV and Y'UV were used for a specific analog encoding 
of color information in television systems, while YCbCr was used for digital 
encoding of color information suited for video and still-image compression and 
transmission such as MPEG and JPEG. Today, the term YUV is commonly used in 
the computer industry to describe file-formats that are encoded using YCbCr."

V4L2 seems to suffer from the ambiguity, as we use YUV as generic term to mean 
a digital luma/chroma format. I thus think your driver should use the existing 
YUV pixel codes.

-- 
Regards,

Laurent Pinchart
--
To unsubscribe from this list: send the line "unsubscribe linux-media" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [Linux Input]     [Video for Linux]     [Gstreamer Embedded]     [Mplayer Users]     [Linux USB Devel]     [Linux Audio Users]     [Linux Kernel]     [Linux SCSI]     [Yosemite Backpacking]
  Powered by Linux