Struct GainMapMetadata 

pub struct GainMapMetadata {
    pub is_multichannel: bool,
    pub use_base_colour_space: bool,
    pub backward_direction: bool,
    pub base_hdr_headroom_n: u32,
    pub base_hdr_headroom_d: u32,
    pub alternate_hdr_headroom_n: u32,
    pub alternate_hdr_headroom_d: u32,
    pub channels: [GainMapChannel; 3],
}

Gain map metadata from a ToneMapImage (tmap) derived image item.

Describes how to apply a gain map to convert between SDR and HDR renditions. The gain map is a separate AV1-encoded image that, combined with this metadata, allows reconstructing an HDR image from the SDR base.

See ISO 21496-1:2025 for the full specification.

Fields

is_multichannel: bool

If true, each RGB channel has independent gain map parameters. If false, channels[0] applies to all three channels.

use_base_colour_space: bool

If true, the gain map is encoded in the base image’s colour space. If false, it’s in the alternate image’s colour space.

backward_direction: bool

ISO 21496-1 backward direction flag (bit 2 of flags byte). When true, the base image is HDR and the alternate is SDR. Default false = base is SDR, alternate is HDR.

base_hdr_headroom_n: u32

Base HDR headroom (numerator).

base_hdr_headroom_d: u32

Base HDR headroom (denominator).

alternate_hdr_headroom_n: u32

Alternate HDR headroom (numerator).

alternate_hdr_headroom_d: u32

Alternate HDR headroom (denominator).

channels: [GainMapChannel; 3]

Per-channel parameters. For single-channel mode, only index 0 is meaningful (indices 1 and 2 are copies of index 0).

Implementations

impl GainMapMetadata

pub fn parse_tmap_bytes(data: &[u8]) -> Result<Self>

Parse an ISO 21496-1 AVIF tmap item payload into a GainMapMetadata.

This is the public mirror of the internal parser. Useful for testing and for consumers who hold raw tmap payload bytes.

pub fn to_bytes(&self) -> Vec<u8>

Serialize this metadata to the ISO 21496-1 AVIF tmap item payload format.

This is the inverse of the internal parse_tone_map_image function and produces the exact byte sequence expected in an AVIF tmap item. The output can be passed to zenavif_serialize::Aviffy::set_gain_map or used for byte-level roundtrip testing.

Always writes the full (non-common-denominator) wire form: inputs that were parsed from the FLAG_COMMON_DENOMINATOR compact layout are re-expanded to per-field (numerator, denominator) pairs and the compact form is NOT preserved.

version and minimum_version are always written as 0. Writer version is always emitted as 0 (we don’t claim any extensions beyond the base ISO 21496-1 spec).

Trait Implementations

impl Clone for GainMapMetadata

fn clone(&self) -> GainMapMetadata

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for GainMapMetadata

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

Formats the value using the given formatter.

impl Eq for GainMapMetadata

impl From<&GainMapMetadata> for GainMapParams

fn from(md: &GainMapMetadata) -> Self

Converts to this type from the input type.

impl From<&GainMapParams> for GainMapMetadata

fn from(p: &GainMapParams) -> Self

Converts to this type from the input type.

impl PartialEq for GainMapMetadata

fn eq(&self, other: &GainMapMetadata) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for GainMapMetadata