On 3/5/20, mindm...@gmail.com <mindm...@gmail.com> wrote:
> From: Mark Reid <mindm...@gmail.com>
>
> Hi,
> The following patch adds a cineon lin2log color transfer characteristic to
> exr.
> The purpose of this patch is to allow preserving of the dynamic range of an
> exr file when converting to DPX or when using video filter such as 3d luts.
> I wasn't sure if adding it to the AVColorTransferCharacteristic enum was the
> correct approach as this might be a exr specific thing but I figured it was
> a good starting point.
>
> ---
> libavcodec/exr.c | 2 ++
> libavutil/color_utils.c | 14 ++++++++++++++
> libavutil/pixfmt.h | 1 +
> 3 files changed, 17 insertions(+)
>
> diff --git a/libavcodec/exr.c b/libavcodec/exr.c
> index 1db30a1ae0..f2900a7921 100644
> --- a/libavcodec/exr.c
> +++ b/libavcodec/exr.c
> @@ -1938,6 +1938,8 @@ static const AVOption options[] = {
> AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_SMPTEST2084 }, INT_MIN,
> INT_MAX, VD, "apply_trc_type"},
> { "smpte428_1", "SMPTE ST 428-1", 0,
> AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_SMPTEST428_1 }, INT_MIN,
> INT_MAX, VD, "apply_trc_type"},
> + { "lin2log", "Default Cineon/DPX log", 0,
> + AV_OPT_TYPE_CONST, {.i64 = AVCOL_TRC_CINE_LIN2LOG }, INT_MIN,
> INT_MAX, VD, "apply_trc_type"},
>
> { NULL },
> };
> diff --git a/libavutil/color_utils.c b/libavutil/color_utils.c
> index eb8bc7b5fc..e33c019d4a 100644
> --- a/libavutil/color_utils.c
> +++ b/libavutil/color_utils.c
> @@ -167,6 +167,16 @@ static double avpriv_trc_arib_std_b67(double Lc) {
> (Lc <= 1.0 / 12.0 ? sqrt(3.0 * Lc) : a * log(12.0 * Lc - b) + c);
> }
>
> +static double avpriv_trc_cine_lin2log(double Lc) {
> + const double blackpoint = 95.0;
> + const double whitepoint = 685.0;
> + const double gamma = 0.6;
> + const double offset = pow(10, (blackpoint - whitepoint) * 0.002 /
> gamma);
> + const double gain = 1.0 / (1.0 - offset);
> +
> + return (log10((Lc + offset) / gain) / (0.002 / gamma) + whitepoint ) /
> 1023.0;
> +}
> +
> avpriv_trc_function avpriv_get_trc_function_from_trc(enum
> AVColorTransferCharacteristic trc)
> {
> avpriv_trc_function func = NULL;
> @@ -225,6 +235,10 @@ avpriv_trc_function
> avpriv_get_trc_function_from_trc(enum AVColorTransferCharact
> func = avpriv_trc_arib_std_b67;
> break;
>
> + case AVCOL_TRC_CINE_LIN2LOG:
> + func = avpriv_trc_cine_lin2log;
> + break;
> +
> case AVCOL_TRC_RESERVED0:
> case AVCOL_TRC_UNSPECIFIED:
> case AVCOL_TRC_RESERVED:
> diff --git a/libavutil/pixfmt.h b/libavutil/pixfmt.h
> index 1c625cfc8a..1f3f9988d7 100644
> --- a/libavutil/pixfmt.h
> +++ b/libavutil/pixfmt.h
> @@ -499,6 +499,7 @@ enum AVColorTransferCharacteristic {
> AVCOL_TRC_SMPTE428 = 17, ///< SMPTE ST 428-1
> AVCOL_TRC_SMPTEST428_1 = AVCOL_TRC_SMPTE428,
> AVCOL_TRC_ARIB_STD_B67 = 18, ///< ARIB STD-B67, known as "Hybrid
> log-gamma"
> + AVCOL_TRC_CINE_LIN2LOG = 19, ///< Default Cineon/DPX linear to log 1D
> curve
I do not think this one is correct.
> AVCOL_TRC_NB ///< Not part of ABI
> };
>
> --
> 2.21.0
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