[vlc-devel] [PATCH 1/3] picture: round visible pitch/line to the upper integer

[Steve Lhomme]

On Thu, Mar 23, 2017 at 11:23 AM, Rémi Denis-Courmont <remi at remlab.net> wrote:
> On March 23, 2017 9:37:23 AM GMT+02:00, Steve Lhomme <robux4 at gmail.com> wrote:
>>On Wed, Mar 22, 2017 at 5:01 PM, Rémi Denis-Courmont <remi at remlab.net>
>>wrote:
>>> Le keskiviikkona 22. maaliskuuta 2017, 16.50.49 EET Steve Lhomme a
>>écrit :
>>>> From: Steve Lhomme <robUx4 at videolabs.io>
>>>>
>>>> Otherwise in cases where there's pixel sub-sampling we may miss some
>>visible
>>>> sub pixels.
>>>
>>> I am not sure that this is correct. While it is annoying to handle,
>>it is not
>>> necessarily incorrect for the visible dimensions to not follow
>>macropixel
>>> boundaries.
>>
>>Let's say you have a I420 of 3x3 visible pixels. The Y plane is 3x3 of
>>visible pixels. The U and V planes can either be 1x1 or 2x2 visible
>>pixels. In the first case you will be constructing the last row with
>>pixels that are not meant to be visible and so possibly not copied
>>(most plane copies only copy the visible lines, no more). This seems
>>bogus to me. The 2x2 pixels are actually data that should be filled by
>>the decoder with data that were actually encoded.
>>
>>> --
>>> 雷米‧德尼-库尔蒙
>>> https://www.remlab.net/
>>>
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> The coded dimensions must be aligned on macropixels. I don't see why visible dimensions would need to. This is especially obvious in case of cropping.

Because they are actual pixels to display. They need their proper Y, U
and V values to be rendered correctly. We don't want to lose these
during a plane copy.

> -
> Rémi Denis-Courmont
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