Re: [FFmpeg-devel] [PATCH 3/5] avcodec/fflcms2: add ff_icc_profile_sanitize

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Niklas Haas:
> From: Niklas Haas <git@haasn.dev>
> 
> Buggy ICCv4 profiles are unfortunately used in the wild, and it's quite
> easy to work around them by just forcing the white point to the correct
> value. Display a warning just in case.
> 
> See-Also: https://trac.ffmpeg.org/ticket/9673
> ---
>  libavcodec/fflcms2.c | 45 ++++++++++++++++++++++++++++++++++++++++++++
>  libavcodec/fflcms2.h |  7 +++++++
>  2 files changed, 52 insertions(+)
> 
> diff --git a/libavcodec/fflcms2.c b/libavcodec/fflcms2.c
> index 5443f178bc9..41732c9c862 100644
> --- a/libavcodec/fflcms2.c
> +++ b/libavcodec/fflcms2.c
> @@ -201,6 +201,51 @@ static av_always_inline void XYZ_xy(cmsCIEXYZ XYZ, AVCIExy *xy)
>      xy->y = av_d2q(k * XYZ.Y, 100000);
>  }
>  
> +static const AVCIExy wp_d50 = { {3457, 10000}, {3585, 10000} }; /* CIE D50 */
> +
> +int ff_icc_profile_sanitize(FFIccContext *s, cmsHPROFILE profile)
> +{
> +    cmsCIEXYZ *white, fixed;
> +    AVCIExy wpxy;
> +    AVRational diff, z;
> +    if (!profile)
> +        return 0;
> +
> +    if (cmsGetEncodedICCversion(profile) >= 0x4000000) { // ICC v4
> +        switch (cmsGetHeaderRenderingIntent(profile)) {
> +        case INTENT_RELATIVE_COLORIMETRIC:
> +        case INTENT_ABSOLUTE_COLORIMETRIC: ;
> +            /* ICC v4 colorimetric profiles are specified to always use D50
> +             * media white point, anything else is a violation of the spec.
> +             * Sadly, such profiles are incredibly common (Apple...), so make
> +             * an effort to fix them. */
> +            if (!(white = cmsReadTag(profile, cmsSigMediaWhitePointTag)))
> +                return AVERROR_INVALIDDATA;
> +            XYZ_xy(*white, &wpxy);
> +            diff = av_add_q(av_abs_q(av_sub_q(wpxy.x, wp_d50.x)),
> +                            av_abs_q(av_sub_q(wpxy.y, wp_d50.y)));
> +            if (av_cmp_q(diff, av_make_q(1, 1000)) > 0) {
> +                av_log(s->avctx, AV_LOG_WARNING, "Invalid colorimetric ICCv4 "
> +                       "profile media white point tag (expected %.4f %.4f, "
> +                       "got %.4f %.4f)\n",
> +                       av_q2d(wp_d50.x), av_q2d(wp_d50.y),
> +                       av_q2d(wpxy.x), av_q2d(wpxy.y));

Will this warn on every frame?

> +                /* x+y+z = 1 */
> +                z = av_sub_q(av_sub_q(av_make_q(1, 1), wp_d50.x), wp_d50.y);
> +                fixed.X = av_q2d(av_div_q(wp_d50.x, wp_d50.y)) * white->Y;
> +                fixed.Y = white->Y;
> +                fixed.Z = av_q2d(av_div_q(z, wp_d50.y)) * white->Y;
> +                if (!cmsWriteTag(profile, cmsSigMediaWhitePointTag, &fixed))
> +                    return AVERROR_EXTERNAL;
> +            }
> +            break;
> +        default: break;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
>  int ff_icc_profile_read_primaries(FFIccContext *s, cmsHPROFILE profile,
>                                    AVColorPrimariesDesc *out_primaries)
>  {
> diff --git a/libavcodec/fflcms2.h b/libavcodec/fflcms2.h
> index af63c9a13c8..b54173e50e2 100644
> --- a/libavcodec/fflcms2.h
> +++ b/libavcodec/fflcms2.h
> @@ -65,6 +65,13 @@ int ff_icc_profile_generate(FFIccContext *s,
>   */
>  int ff_icc_profile_attach(FFIccContext *s, cmsHPROFILE profile, AVFrame *frame);
>  
> +/**
> + * Sanitize an ICC profile to try and fix badly broken values.
> + *
> + * Returns 0 on success, or a negative error code.
> + */
> +int ff_icc_profile_sanitize(FFIccContext *s, cmsHPROFILE profile);

Why is this a separate function and not just a new parameter to
ff_icc_profile_read_primaries() given that these seem to always be used
a pair?

- Andreas

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