Re: [FFmpeg-devel] [PATCH 1/3] avfilter/vf_colordetect: add new color range detection filter

From: Niklas Haas <ffmpeg@haasn.xyz>
To: ffmpeg-devel@ffmpeg.org
Cc: Niklas Haas <git@haasn.dev>
Subject: Re: [FFmpeg-devel] [PATCH 1/3] avfilter/vf_colordetect: add new color range detection filter
Date: Wed, 16 Jul 2025 17:48:56 +0200
Message-ID: <20250716174856.GB373337@haasn.xyz> (raw)
In-Reply-To: <20250716152551.362334-1-ffmpeg@haasn.xyz>

On Wed, 16 Jul 2025 17:25:49 +0200 Niklas Haas <ffmpeg@haasn.xyz> wrote:
> From: Niklas Haas <git@haasn.dev>
>
> This filter can detect various properties about the image, including
> whether or not there are out-of-range values, or whether the input appears
> to use straight or premultiplied alpha.
>
> Of course, these can only be heuristics, with "undetermined" as the base
> case. While we can definitely prove the existence of full range or
> straight alpha colors, we can never infer the opposite.

Upon further testing, I realized that this logic (both C and SIMD) overflows
for 16-bit inputs. Will fix and resubmit.

I also found that the C versions can be made slightly faster by returning out
of the inner loop, which generates a shorter scalar version that is faster
than the auto-vectorized abomination that was generated before.
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