Struct SplitConfig 

pub struct SplitConfig {
    pub luma_weights: [f32; 3],
    pub base_offset: f32,
    pub alternate_offset: f32,
    pub min_log2: f32,
    pub max_log2: f32,
    pub pre_desaturate: f32,
    pub hlg_ootf_mode: HlgOotfMode,
}

Splitter configuration.

Defaults are chosen so the splitter “just works” with any qualifying curve, including shadow-lifters like BT.2446 Method A. The min_log2 and max_log2 fields are safety clamps that prevent infinite gain at black or unreasonable values from numerical edge cases — they are not quality knobs. The actual gain range to store in zencodec::GainMapChannel.{min,max} should come from the SplitStats::observed_min_log2 / SplitStats::observed_max_log2 after a pass over the image.

Fields

luma_weights: [f32; 3]

RGB → Y weights. Must match the input primaries. Default: LUMA_BT2020.

base_offset: f32

Offset on the base (SDR) image. Maps to GainMapChannel.base_offset. Default 1/64 matches ultrahdr-core::GainMapConfig.

alternate_offset: f32

Offset on the alternate (HDR) image. Maps to GainMapChannel.alternate_offset. Default 1/64 matches ultrahdr-core::GainMapConfig.

min_log2: f32

Sanity floor on log2 gain. Default -4.0 (1/16×) tolerates shadow-lifting curves like BT.2446 Method A.

max_log2: f32

Sanity ceiling on log2 gain. Default 6.0 (64×) covers Apple Ultra HDR’s ~9-stop headroom plus margin.

pre_desaturate: f32

Pre-desaturation (crosstalk) parameter in [0.0, 0.33).

Before the chromaticity-preserving RGB rescale, each HDR channel is blended toward the pixel’s mean:

R' = (1 − 2α)·R + α·G + α·B

This pulls saturated primaries toward gray, reducing the chance that the SDR rescale pushes a channel above 1.0 (out-of-gamut). The inverse matrix is applied after the gain is computed, so the desaturation is transparent to the round-trip.

0.0 = disabled (default). 0.10 is a conservative starting point; BT.2446-C uses up to 0.33 (but 0.33 is degenerate — collapses to grayscale).

hlg_ootf_mode: HlgOotfMode

HLG OOTF formula used when linearizing HLG inputs.

Default: crate::pipeline::HlgOotfMode::Exact — spec-correct, luminance-preserving.

Set to crate::pipeline::HlgOotfMode::LibultrahdrCompat for bit-parity with libultrahdr’s encode path, which uses per-channel pow(c, γ). Only affects LumaGainMapSplitter::split_hlg_row / LumaGainMapSplitter::apply_hlg_row (and the public crate::gainmap::hlg_to_normalized_linear_row_with_mode helper); PQ paths are unaffected.

Trait Implementations

impl Clone for SplitConfig

fn clone(&self) -> SplitConfig

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for SplitConfig

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Default for SplitConfig

fn default() -> SplitConfig

Returns the “default value” for a type.

impl Copy for SplitConfig