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

[Rémi Denis-Courmont]

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.
-- 
Rémi Denis-Courmont