Re: [FFmpeg-devel] [PATCH] avfilter: add inverse tone mapping

[Sarthak Indurkhya via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

Thank you for the thoughtful feedback.

Advantages over vf_libplacebo’s inverse tone mapping:

  1.  Algorithmic Differentiation:
My filter is based on a novel local adaptation + inverse tone mapping strategy specifically tailored to enhance perceptual brightness while preserving spatial detail.

       My implementation uses:

     *   Local bilateral filtering over luminance for content-adaptive scaling.
     *   Dynamic inverse tone mapping via (R / (1 - R))^1/n style reparameterization.
     *   Chromatic scaling to preserve original hues during dynamic range expansion.
  1.  Color Fidelity & HDR Metadata:
     *   The filter performs color space conversion from BT.709 to BT.2020 explicitly and integrates PQ transfer function encoding with full support for mastering metadata (mastering_display_primaries, content_light_level, etc.).
     *   It incorporates localized tone curve shaping, white balance, and chroma boosting that target HDR presentation aesthetics more directly.
  2.  Customizability:
     *   Parameters like sigma_spatial, sigma_range, n, and hdr_max allow users to tailor the HDR expansion according to scene content or output requirements.

I agree that a GPU-based real-time implementation would be valuable. The algorithm I've used is highly parallelizable and very well-suited for implementation as a GPU shader


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From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> on behalf of Kacper Michajlow <kasper93@gmail.com>
Date: Saturday, 19 July 2025 at 8:18 PM
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH] avfilter: add inverse tone mapping
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On Sat, 19 Jul 2025 at 16:13, Sarthak Indurkhya via ffmpeg-devel <
ffmpeg-devel@ffmpeg.org> wrote:

> Hello FFmpeg developers,
> This patch introduces a new video filter called inversetonemap for FFmpeg.
> The filter performs SDR to HDR conversion by mapping SDR BT.709 video to
> HDR BT.2020 PQ, using local adaptation and inverse tone mapping. The goal
> is to provide a simple, flexible tool for upconverting SDR content for HDR
> displays, with local adaptation, tone curve sensitivity, and chroma
> processing.
>
> Please review.
> Thanks,
> Sarthak
>
>
>
Interesting. Could you describe what are the advantages of the new filter,
compared to existing solutions like vf_libplacebo inverse tone mapping?
Additionally if there is a big gap in libplacebo's inverse tone mapping
quality would you be interested in improving the libplacebo implementation
in addition to this filter? I think there would be a gain in having real
time gpu implementation too.

- Kacper
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