[FFmpeg-user] alphamerge filter use problem

[Paul B Mahol]

On 4/12/13, Paul B Mahol <onemda at gmail.com> wrote:
> On 4/12/13, Tim Willison <timbot at oddlystudios.com> wrote:
>> Hello folks,
>> I thought I could share a tip I've used in my experiments with the
>> alphaextract and alphamerge filters.
>>
>> I have found that the result of the alphamerge filter often leaves areas
>> with some non-zero alpha. Comparing the mask file, areas that are pure
>> black are not always reproduced as pure alpha after the merge.
>
> Looks like you used YUV source for mask. And result is expected because
> YUV (limited range, not YUVJ) values can not be 0-16 or 235-255.

Not including 16 and 235, thus allowed values are from 16 to 235.