[x264-devel] x264 bug: interlaced video missing grain/detail in top 32 lines

[Adam Warner]

On Fri, 2010-03-12 at 05:42 -0800, Jason Garrett-Glaser wrote:
> On Fri, Mar 12, 2010 at 5:27 AM, Adam Warner <lists at consulting.net.nz> wrote:
> > Hi all,
> >
> > I have found a bug in x264's interlacing.
> 
> This is not a bug.  This is intentional, and part of how adaptive
> quantization works.  If you want to avoid it, don't stick gigantic
> black bars on the top of your videos.

This explains why I was unable to reproduce the missing grain/detail in
the top 32 lines of other (borderless) grainy video clips.

It's good to learn about this limitation of the adaptive quantization
algorithm. Since interlaced fields are expanded into full height frames
the missing grain/detail is, unfortunately, twice as pronounced.

Thanks for all your great work on x264. I've recently enjoyed reading
your blogging about the complexities of film grain optimization and
wavelets. Since you have a big Blu-Ray compatibility release coming up
soon I wanted to ensure no bugs crept in. Sorry I was mistaken about
x264's output in this instance being a bug.

Regards,
Adam