linux-kernel - Re: [PATCH] media: doc: pixfmt-yuv: Fix 4:4:4 subsampling info

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Date:   Mon, 25 Jan 2021 16:07:41 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Helen Koike <helen.koike@...labora.com>
Cc:     linux-media@...r.kernel.org, hverkuil@...all.nl,
        hans.verkuil@...co.com, kernel@...labora.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: doc: pixfmt-yuv: Fix 4:4:4 subsampling info

Hi Helen,

On Mon, Jan 25, 2021 at 11:02:01AM -0300, Helen Koike wrote:
> On 1/25/21 10:57 AM, Helen Koike wrote:
> > On 1/23/21 6:56 AM, Laurent Pinchart wrote:
> >> On Fri, Jan 22, 2021 at 03:27:23PM -0300, Helen Koike wrote:
> >>> YUV 4:4:4 is not subsampled, fix this in the docs.
> >>>
> >>> Fixes: da785536e007 ("media: doc: pixfmt-yuv: Move all semi-planar YUV formats to common file")
> >>> Signed-off-by: Helen Koike <helen.koike@...labora.com>
> >>> ---
> >>>  Documentation/userspace-api/media/v4l/pixfmt-yuv-planar.rst | 4 ++--
> >>>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/Documentation/userspace-api/media/v4l/pixfmt-yuv-planar.rst b/Documentation/userspace-api/media/v4l/pixfmt-yuv-planar.rst
> >>> index 7d4d39201a3f..bcb4ef24c334 100644
> >>> --- a/Documentation/userspace-api/media/v4l/pixfmt-yuv-planar.rst
> >>> +++ b/Documentation/userspace-api/media/v4l/pixfmt-yuv-planar.rst
> >>> @@ -396,8 +396,8 @@ number of lines as the luma plane.
> >>>  NV24 and NV42
> >>>  -------------
> >>>  
> >>> -Semi-planar YUV 4:4:4 formats. The chroma plane is subsampled by 2 in the
> >>> -horizontal direction. Chroma lines contain half the number of pixels and the
> >>> +Semi-planar YUV 4:4:4 formats. No sub-sampling.
> >>
> >> "The chroma plane is not subsampled." ?
> > 
> > Ack.
> > 
> >>> +Chroma lines contain the same number of pixels and the
> >>>  same number of bytes as luma lines, and the chroma plane contains the same
> >>>  number of lines as the luma plane.
> >>
> >> That's not quite right, the chroma lines contain twice the number of
> >> pixels and bytes, as there's one Cb and one Cr value in the chroma line
> >> for each Y value in the luma line.
> 
> Actually, it is the same number o pixels, but twice the number o bytes.
> Since a trio (YCbCr) compose a pixel.
> 
> At least this is how I understand comparing the logic of the text description
> of NV16 YUV4:2:2.

You're right, my bad.

> >> Maybe the text could be reflowed ?
> > 
> > Ack.
> > 
> > I'll submit v2 updating the text.

-- 
Regards,

Laurent Pinchart