Struct LosslessConfig 

pub struct LosslessConfig { /* private fields */ }

Lossless (modular) encoding configuration.

Has a sensible Default — lossless has no quality ambiguity.

Implementations

impl LosslessConfig

pub fn new() -> Self

Create a new lossless config with defaults (effort 7).

pub fn with_effort(self, effort: u8) -> Self

Set effort level (1–10). Higher effort = slower, better compression.

This adjusts all effort-dependent defaults:

• e1–3: Huffman encoding
• e4–6: + ANS entropy coding
• e7: + content-adaptive tree learning, LZ77 RLE
• e8: + LZ77 greedy hash chain
• e9–10: + LZ77 optimal (Viterbi DP)

Individual with_*() calls after with_effort() override these defaults.

pub fn with_mode(self, mode: EncoderMode) -> Self

Set encoder mode (default: EncoderMode::Reference).

Reference matches libjxl’s algorithm choices for comparable output. Experimental enables encoder-specific improvements.

pub fn mode(&self) -> EncoderMode

Current encoder mode.

pub fn with_patches(self, enable: bool) -> Self

Enable/disable patches (dictionary-based repeated pattern detection). Default: true at effort >= 5. Huge wins on screenshots, zero cost on photos.

pub fn with_ans(self, enable: bool) -> Self

Enable/disable ANS entropy coding (default: true).

pub fn with_squeeze(self, enable: bool) -> Self

Enable/disable squeeze (Haar wavelet) transform (default: false).

Squeeze is disabled by default because tree learning provides better compression on both photos and screenshots. Squeeze can still be enabled via .with_squeeze(true) for experimentation.

pub fn with_tree_learning(self, enable: bool) -> Self

Enable/disable content-adaptive tree learning (default: false).

pub fn with_lz77(self, enable: bool) -> Self

Enable/disable LZ77 backward references (default: false).

pub fn with_lz77_method(self, method: Lz77Method) -> Self

Set LZ77 method (default: Greedy). Only effective when LZ77 is enabled.

pub fn with_lossy_palette(self, enable: bool) -> Self

Enable/disable lossy delta palette (default: false).

When enabled, uses quantized palette with delta entries and error diffusion for near-lossless encoding. This is NOT pixel-exact — it trades some color accuracy for significantly smaller files on images with many colors. Matching libjxl’s modular lossy palette mode.

pub fn with_threads(self, threads: usize) -> Self

Set thread count for parallel encoding.

• 0 (default): use the ambient rayon pool. The caller can control thread count by wrapping the encode call in pool.install(|| ...).
• 1: force sequential encoding (no rayon).
• N >= 2: create a dedicated N-thread pool for this encode.

Requires the parallel feature. When parallel is not enabled, this value is ignored and encoding is always sequential.

pub fn effort(&self) -> u8

Current effort level.

pub fn ans(&self) -> bool

Whether ANS entropy coding is enabled.

pub fn squeeze(&self) -> bool

Whether squeeze (Haar wavelet) transform is enabled.

pub fn tree_learning(&self) -> bool

Whether content-adaptive tree learning is enabled.

pub fn lz77(&self) -> bool

Whether LZ77 backward references are enabled.

pub fn lz77_method(&self) -> Lz77Method

Current LZ77 method.

pub fn patches(&self) -> bool

Whether patches (dictionary-based repeated pattern detection) are enabled.

pub fn lossy_palette(&self) -> bool

Whether lossy delta palette is enabled.

pub fn threads(&self) -> usize

Thread count (0 = auto, 1 = sequential).

pub fn encode_request( &self, width: u32, height: u32, layout: PixelLayout, ) -> EncodeRequest<'_>

Create an encode request for an image with this config.

Use this when you need to attach metadata, limits, or cancellation.

pub fn encode( &self, pixels: &[u8], width: u32, height: u32, layout: PixelLayout, ) -> Result<Vec<u8>>

Encode pixels directly with this config. Shortcut for simple cases.

let jxl = jxl_encoder::LosslessConfig::new()
    .encode(&pixels, 100, 100, jxl_encoder::PixelLayout::Rgb8)?;

pub fn encode_into( &self, pixels: &[u8], width: u32, height: u32, layout: PixelLayout, out: &mut Vec<u8>, ) -> Result<()>

Encode pixels, appending to an existing buffer.

pub fn encode_animation( &self, width: u32, height: u32, layout: PixelLayout, animation: &AnimationParams, frames: &[AnimationFrame<'_>], ) -> Result<Vec<u8>>

Encode a multi-frame animation as a lossless JXL.

Each frame must have the same dimensions and pixel layout. Returns the complete JXL codestream bytes.

impl LosslessConfig

pub fn encoder( &self, width: u32, height: u32, layout: PixelLayout, ) -> Result<LosslessEncoder>

Create a streaming encoder for incremental row input.

Per-channel planes are pre-allocated and filled as rows are pushed via LosslessEncoder::push_rows, allowing callers to free source buffers incrementally rather than materializing the entire image.

Trait Implementations

impl Clone for LosslessConfig

fn clone(&self) -> LosslessConfig

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for LosslessConfig

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

Formats the value using the given formatter.

impl Default for LosslessConfig

fn default() -> Self

Returns the “default value” for a type.