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

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

[Helen Koike]

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@collabora.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.
+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.
 
-- 
2.30.0

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

[Laurent Pinchart]

Hi Helen,

Thank you for the patch.

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@collabora.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." ?

> +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.


Maybe the text could be reflowed ?

-- 
Regards,

Laurent Pinchart

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

[Helen Koike]

On 1/23/21 6:56 AM, Laurent Pinchart wrote:
> Hi Helen,
> 
> Thank you for the patch.
> 
> 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@collabora.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.
> 
> 
> Maybe the text could be reflowed ?
> 

Ack.

I'll submit v2 updating the text.

Thanks,
Helen

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

[Helen Koike]

On 1/25/21 10:57 AM, Helen Koike wrote:
> 
> 
> On 1/23/21 6:56 AM, Laurent Pinchart wrote:
>> Hi Helen,
>>
>> Thank you for the patch.
>>
>> 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@collabora.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.

Regards,
Helen

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

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

[Laurent Pinchart]

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@collabora.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