dithr 0.2.0

# dithr 0.2.0 - Remaining PR Context (Delta Only)

This file contains only remaining 0.2.0 work.
Already-implemented items are intentionally omitted.

## Global Rules

1. Keep deterministic behavior in all algorithm paths.
2. Keep existing public algorithm names; add new overloads/wrappers only.
3. Keep `u8` ergonomics first-class.
4. Do not merge multiple PR scopes into one.
5. Run `fmt`, `clippy`, and `test` after each PR.
6. If a golden hash changes, document the reason in the PR description.
7. Parallelism policy for 0.2.0: only Yliluoma receives new `_par` APIs; diffusion and advanced families remain serial to preserve canonical deterministic output.

## Parallelism Evaluation (All PRs)

| PR | New Parallel API in PR | Decision |
| --- | --- | --- |
| PR00 | No | `No` |
| PR01 | No | `No` |
| PR02 | Yes | `Yes` (`yliluoma_*_in_place_par` only) |
| PR03 | No | `No` |
| PR04 | No | `No` |
| PR05 | No | `No` |
| PR06 | No | `No` |
| PR07 | No | `No` |
| PR08 | No | `No` |
| PR09 | No | `No` |
| PR10 | No | `No` |
| PR11 | No | `No` |
| PR12 | No | `No` |
| PR13 | No | `No` |
| PR14 | No | `No` |
| PR15 | No | `No` |
| PR16 | No | `No` |
| PR17 | No | `No` |
| PR18 | No | `No` |
| PR19 | No | `No` |
| PR20 | No | `No` |
| PR21 | No | `No` |
| PR22 | No | `No` |
| PR23 | No | `No` |
| PR24 | No | `No` |
| PR25 | No | `No` |
| PR26 | No | `No` |
| PR27 | No | `No` |
| PR28 | No | `No` |
| PR29 | No | `No` |
| PR31 | No | `No` |
| PR32 | No | `No` |
| PR33 | No | `No` |
| PR34 | No | `No` |

## Consolidated Algorithm Bundles (Use These Instead of Separate PR07-PR34)

Use the consolidated bundles below for implementation planning.  
They preserve full scope from the original per-algorithm PRs but reduce churn by grouping methods that share core math and file touch sets.

### CAPR-A - Ordered Adaptive/Traversal Methods

Combines:
- PR20 (adaptive ordered dither)
- PR21 (space-filling curve ordered dither)
- PR22 (ranked dither)

Why grouped:
- Same family (`src/ordered/*`)
- Shared rank-map/traversal concepts
- Shared test/golden/bench plumbing

Parallelism:
- `No` (serial only in 0.2.0)

### CAPR-B - Ordered Screen-Synthesis Methods

Combines:
- PR07 (void-and-cluster blue-noise ordered)
- PR23 (image-based dither screens)
- PR25 (stochastic clustered-dot)
- PR24 (polyomino ordered dithering)

Why grouped:
- Same family (`src/ordered/*`)
- All are threshold/screen construction pipelines feeding ordered core
- Common deterministic map/screen generation concerns

Parallelism:
- `No` (serial only in 0.2.0)

### CAPR-C - Multiscale Error-Diffusion Suite

Combines:
- PR09 (multiscale error diffusion)
- PR10 (feature-preserving MSED)
- PR11 (green-noise MSED)

Why grouped:
- Same multiscale scaffold and level traversal
- Same file set (`src/diffusion/variable.rs`, `src/diffusion/mod.rs`)

Parallelism:
- `No` (serial only in 0.2.0)

### CAPR-D - Color/Vector Error-Diffusion Suite

Combines:
- PR12 (adaptive vector ED)
- PR16 (vector + semivector ED)
- PR17 (hierarchical ED)

Why grouped:
- Shared vector-valued color error propagation and coefficient plumbing
- Same tests/fixtures and alpha-preservation concerns

Parallelism:
- `No` (serial only in 0.2.0)

### CAPR-E - Grayscale Quality-Driven ED Suite

Combines:
- PR15 (HVS-optimized ED)
- PR18 (tone-dependent ED)
- PR19 (structure-aware ED)

Why grouped:
- Shared grayscale-focused variable/quality control pathways
- Same module and bench footprint

Parallelism:
- `No` (serial only in 0.2.0)

### CAPR-F - Search/Model-Based Advanced Halftoning Suite

Combines:
- PR14 (model-based MED + LSMB)
- PR26 (clustered-dot direct multi-bit search)
- PR28 (hierarchical colorant DBS)

Why grouped:
- Shared optimization-style loops in advanced/dbs paths
- Common objective instrumentation and convergence tests

Parallelism:
- `No` (serial only in 0.2.0)

### CAPR-G - Direct Pattern Control Halftoning

Equivalent to:
- PR27 (direct pattern control)

Parallelism:
- `No` (serial only in 0.2.0)

### CAPR-H - Optimized Dot Diffusion

Equivalent to:
- PR08 (optimized dot diffusion)

Parallelism:
- `No` (serial only in 0.2.0)

### CAPR-I - MBVQ/Neugebauer Color Error-Diffusion Branch

Combines:
- PR29 (MBVQ/MBVC + Neugebauer-model color ED)

Why grouped:
- Recognizable classical color-halftoning branch
- Distinct design rule beyond scalar/vector ED and DBS-style search families
- Shared Neugebauer/MBVQ color-selection infrastructure

Parallelism:
- `No` (serial only in 0.2.0)

### CAPR-J - Block/Mask/Multitone Halftoning Suite

Combines:
- PR31 (block error diffusion)
- PR32 (multichannel green-noise mask diffusion)
- PR33 (AM/FM hybrid + clustered AM/FM)
- PR34 (blue-noise multitone dithering)

Why grouped:
- Shared halftone texture/screen design pipeline concerns
- Shared multilevel and mask-design validation needs
- Similar advanced-family benchmark/fixture footprint

Parallelism:
- `No` (serial only in 0.2.0)

---

## PR00 - Module-First Public API Cleanup

### Goal

Make module paths canonical and de-crowd crate-root exports while preserving backward compatibility during 0.2.x.

### Files

- `src/lib.rs`
- `README.md`
- `examples/gray_buffer.rs`
- `examples/rgb_buffer.rs`
- `examples/indexed_palette.rs`
- `examples/image_bayer_png.rs`
- `examples/image_palette_png.rs`
- `tests/basic.rs`

### Exact Changes

1. Keep family modules public and first-class:
   - `buffer`
   - `ordered`
   - `diffusion`
   - `stochastic`
   - `dbs`
   - `palette`
   - `quantize`
   - `riemersma`
2. Keep only core/common items prominently re-exported at root:
   - buffer/value types and typed constructors
   - `QuantizeMode`
   - `Palette` / `IndexedImage`
   - `Error` / `Result`
3. Deprecate root-level algorithm re-exports (do not remove in 0.2.x):
   - `#[deprecated(since = "0.2.0", note = "use dithr::<family>::...")]`
   - include explicit note targets, for example:
     - `ordered::bayer_8x8_in_place`
     - `diffusion::floyd_steinberg_in_place`
     - `dbs::direct_binary_search_in_place`
4. Update examples/tests to import algorithm functions from family modules.
5. Update README import style to module-first paths.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo test --workspace --lib --tests --examples
```

### Sources (https)

- https://rust-lang.github.io/api-guidelines/naming.html
- https://rust-lang.github.io/api-guidelines/dependencies.html
- https://doc.rust-lang.org/cargo/reference/semver.html
- https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-deprecated-attribute

---

## PR01 - DynamicImage LumaA Support Gap

### Goal

Close the adapter gap for `image::DynamicImage::ImageLumaA8` and `ImageLumaA16` without introducing new layout types in this release.

### Files

- `src/adapter.rs`
- `src/lib.rs`
- `README.md`

### Exact Changes

1. Update `dynamic_image_as_buffer` in `src/adapter.rs`:
   - Stop returning `UnsupportedFormat` for `ImageLumaA8` and `ImageLumaA16`.
   - For `ImageLumaA8`, convert in-place to `ImageRgba8` and return `DynamicImageBuffer::Rgba8`.
   - For `ImageLumaA16`, convert in-place to `ImageRgba16` and return `DynamicImageBuffer::Rgba16`.
2. Add internal helpers in `src/adapter.rs`:
   - `promote_lumaa8_to_rgba8`
   - `promote_lumaa16_to_rgba16`
3. Update adapter tests:
   - Replace `dynamic_image_adapter_rejects_lumaa8` with:
     - `dynamic_image_adapter_promotes_lumaa8_to_rgba8`
     - `dynamic_image_adapter_promotes_lumaa16_to_rgba16`
4. Update docs text only where facts changed:
   - `src/lib.rs`: image adapter section should state LumaA is promoted to RGBA.
   - `README.md`: remove the limitation claiming LumaA is unsupported.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo test --workspace --lib --tests --examples
```

### Sources (https)

- https://docs.rs/image/0.24.9/image/enum.DynamicImage.html
- https://docs.rs/image/0.24.9/image/enum.DynamicImage.html#variant.ImageLumaA8
- https://docs.rs/image/0.24.9/image/enum.DynamicImage.html#variant.ImageLumaA16
- https://docs.rs/image/0.24.9/image/enum.DynamicImage.html#method.into_rgba8
- https://docs.rs/image/0.24.9/image/enum.DynamicImage.html#method.into_rgba16

---

## PR02 - Yliluoma Parallel API (Deterministic Canonical-Output Safe)

### Goal

Add `rayon`-gated `_par` wrappers for Yliluoma only, with strict sequential/parallel output identity.

### Files

- `src/ordered/yliluoma.rs`
- `src/ordered/mod.rs`
- `src/lib.rs`
- `tests/ordered.rs`
- `benches/yliluoma.rs`
- `README.md`

### Exact Changes

1. Add `#[cfg(feature = "rayon")]` wrappers in `src/ordered/yliluoma.rs`:
   - `yliluoma_1_in_place_par`
   - `yliluoma_2_in_place_par`
   - `yliluoma_3_in_place_par`
2. Keep algorithm math unchanged.
3. Require byte-identical output vs sequential wrappers on fixed fixtures.
4. Re-export wrappers in `src/ordered/mod.rs` and `src/lib.rs` under `#[cfg(feature = "rayon")]`.
5. Add parity tests in `tests/ordered.rs`:
   - `yliluoma_1_parallel_matches_sequential`
   - `yliluoma_2_parallel_matches_sequential`
   - `yliluoma_3_parallel_matches_sequential`
6. Add `#[cfg(feature = "rayon")]` seq/par benchmark group in `benches/yliluoma.rs`.
7. Update README parallelism section to include Yliluoma, and keep diffusion/advanced listed as serial-only.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://docs.rs/rayon/latest/rayon/iter/trait.ParallelIterator.html
- https://docs.rs/rayon/latest/rayon/slice/trait.ParallelSliceMut.html
- https://docs.rs/rayon/latest/rayon/index.html

---

## PR03 - Public API Compatibility Cleanup (Remaining)

### Goal

Finish compatibility deprecations that are still missing.

### Files

- `src/buffer.rs`
- `src/stochastic.rs`
- `src/adapter.rs`
- `src/lib.rs`
- `tests/basic.rs`

### Exact Changes

1. Mark remaining compatibility aliases as deprecated (do not remove in 0.2.0):
   - `src/buffer.rs`:
     - `gray_f32`
     - `rgb_f32`
     - `rgba_f32`
   - `src/stochastic.rs`:
     - `threshold_in_place`
     - `random_in_place`
   - `src/adapter.rs`:
     - `gray_image_as_buffer`
     - `rgb_image_as_buffer`
     - `rgba_image_as_buffer`
2. Deprecation format:
   - `#[deprecated(since = "0.2.0", note = "...")]`
3. Keep deprecated symbols exported in `src/lib.rs`.
4. Add compatibility tests in `tests/basic.rs` (`#[allow(deprecated)]` in test scope).

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
```

### Sources (https)

- https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-deprecated-attribute
- https://doc.rust-lang.org/cargo/reference/semver.html

---

## PR04 - Panic-Hardening for Custom PixelLayout Paths (Remaining)

### Goal

Finish remaining custom-`PixelLayout` hardening so public entry points return typed errors instead of panicking on invalid downstream layout implementations.

### Files

- `src/core/layout.rs`
- `src/stochastic.rs`
- `src/ordered/core.rs`
- `src/diffusion/core.rs`
- `src/riemersma.rs`
- `src/dot_diffusion.rs`
- `tests/basic.rs`
- `tests/ordered.rs`
- `tests/diffusion.rs`

### Exact Changes

1. Add shared layout-invariant helper in `src/core/layout.rs`:
   - `validate_layout_invariants::<L>() -> crate::Result<()>`
2. Use this helper at top-level family entry points that currently rely on partial ad-hoc checks:
   - stochastic
   - ordered core
   - diffusion core
   - riemersma
   - dot diffusion
3. Keep existing behavior for valid `Gray`/`Rgb`/`Rgba` unchanged.
4. Add malformed-layout tests covering remaining untested public paths.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo test --workspace --lib --tests --examples
```

### Sources (https)

- https://doc.rust-lang.org/book/ch09-00-error-handling.html
- https://rust-lang.github.io/api-guidelines/

---

## PR05 - CI Matrix Completion (Remaining)

### Goal

Add missing `--no-default-features` coverage in CI workflows.

### Files

- `.github/workflows/ci.yml`
- `.github/workflows/scheduled.yml`
- `.github/workflows/msrv.yml`

### Exact Changes

1. `ci.yml`
   - Add:
     - `cargo clippy --workspace --all-targets --no-default-features -- -D warnings`
     - `cargo test --workspace --lib --tests --examples --no-default-features`
2. `scheduled.yml`
   - Add the same missing `--no-default-features` clippy/test runs.
3. `msrv.yml`
   - Add:
     - `cargo check --workspace --all-targets --no-default-features`

### Validation Commands

```bash
cargo clippy --workspace --all-targets -- -D warnings
cargo clippy --workspace --all-targets --no-default-features -- -D warnings
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --lib --tests --examples
cargo test --workspace --lib --tests --examples --no-default-features
cargo test --workspace --all-features --lib --tests --examples
```

### Sources (https)

- https://docs.github.com/en/actions/how-tos/write-workflows/choose-what-workflows-do/run-job-variations
- https://doc.rust-lang.org/cargo/commands/cargo-test.html
- https://doc.rust-lang.org/cargo/commands/cargo-check.html
- https://doc.rust-lang.org/cargo/commands/cargo-clippy.html

---

## PR06 - Bench/Golden Coverage Delta (Remaining)

### Goal

Complete remaining benchmark and golden sensitivity deltas only.

### Files

- `tests/golden.rs`
- `benches/common.rs`
- `benches/ordered.rs`
- `benches/diffusion.rs`

### Exact Changes

1. Bench coverage:
   - Add at least one explicit `f32` path in `benches/ordered.rs`.
   - Add at least one explicit `f32` path in `benches/diffusion.rs`.
   - Add common fixture/helper utilities in `benches/common.rs` only if required to support those two additions.
2. Golden sensitivity:
   - Add only missing distinction checks if any distinct algorithms still share identical canonical fixture hashes after current suite audit.
   - Do not update existing u8 golden hashes unless behavior changes intentionally.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://bheisler.github.io/criterion.rs/book/
- https://crates.io/crates/criterion

---

## PR07 - Void-and-Cluster Blue-Noise Ordered Dithering

### Goal

Add blue-noise ordered dithering via a generated void-and-cluster threshold array.

### Not Already Implemented Check

- No `void`/`blue_noise` ordered algorithm exists in current `src/ordered/*`.
- Current ordered methods are Bayer/cluster-dot/custom only.

### Files

- `src/ordered/void_cluster.rs` (new)
- `src/ordered/mod.rs`
- `src/lib.rs`
- `src/data/maps.rs`
- `tests/ordered.rs`
- `tests/golden.rs`
- `benches/ordered.rs`
- `README.md`

### Exact Changes

1. Add new API:
   - `void_and_cluster_in_place`
2. Use generic ordered core underneath.
3. Add deterministic 64x64 void-and-cluster rank-map generation utility:
   - build once, cache as static map for runtime reuse.
4. Convert generated map to rank array `0..(N-1)` for direct compatibility with existing ordered core.
5. Add tests:
   - deterministic map generation hash check
   - output quantization invariants (`u8`, `u16`, `f32`)
6. Add one ordered bench case for `void_and_cluster_in_place`.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://cv.ulichney.com/papers/1993-void-cluster.pdf
- https://cv.ulichney.com/papers/1994-filter-design.pdf

---

## PR08 - Optimized Dot Diffusion (Beyond Knuth Variant)

### Goal

Add a second dot-diffusion implementation faithful to optimized dot-diffusion literature, separate from the existing Knuth-style variant.

### Not Already Implemented Check

- Current repository has `knuth_dot_diffusion_in_place` only.
- No optimized class-matrix + diffusion-coefficient variant exists.

### Files

- `src/dot_diffusion.rs`
- `src/lib.rs`
- `tests/advanced.rs`
- `tests/golden.rs`
- `benches/advanced.rs`
- `README.md`

### Exact Changes

1. Keep `knuth_dot_diffusion_in_place` unchanged.
2. Add new API:
   - `optimized_dot_diffusion_in_place`
3. Implement optimized-class dot-diffusion path:
   - deterministic class matrix selection
   - deterministic neighborhood weighting consistent with reference method
   - `Gray`/`Rgb`/`Rgba` support with alpha preservation for `Rgba`.
4. Add tests:
   - deterministic fixture hash
   - `u16`/`f32` smoke invariants
   - explicit inequality vs Knuth output on canonical fixture (regression sensitivity).
5. Add one advanced bench case for optimized dot diffusion.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://pubmed.ncbi.nlm.nih.gov/18255440/
- https://doi.org/10.1109/83.841944

---

## PR09 - Multiscale Error Diffusion (MSED)

### Goal

Add canonical multiscale error diffusion as a separate grayscale family member.

### Not Already Implemented Check

- Current diffusion family has classic, extended, variable, and one gradient-based method.
- No multiscale pyramid-style error diffusion implementation exists.

### Files

- `src/diffusion/variable.rs`
- `src/diffusion/mod.rs`
- `src/lib.rs`
- `tests/diffusion.rs`
- `tests/golden.rs`
- `benches/diffusion.rs`
- `README.md`

### Exact Changes

1. Add new API:
   - `multiscale_error_diffusion_in_place`
2. Implement deterministic coarse-to-fine MSED pipeline for grayscale buffers:
   - fixed downsample/upsample policy
   - fixed traversal order at each level
   - deterministic level count from image size.
3. Keep method grayscale-only; return `UnsupportedFormat` for non-gray layouts.
4. Add tests:
   - grayscale-only guard
   - deterministic output hash
   - objective invariants on canonical fixtures.
5. Add one diffusion bench case for MSED.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://pubmed.ncbi.nlm.nih.gov/18282943/
- https://doi.org/10.1109/83.557360

---

## PR10 - Feature-Preserving Multiscale Error Diffusion

### Goal

Add the feature-preserving MSED variant as a second multiscale method.

### Not Already Implemented Check

- No feature-preserving MSED variant exists in current codebase.

### Files

- `src/diffusion/variable.rs`
- `src/diffusion/mod.rs`
- `src/lib.rs`
- `tests/diffusion.rs`
- `tests/golden.rs`
- `benches/diffusion.rs`
- `README.md`

### Exact Changes

1. Add new API:
   - `feature_preserving_msed_in_place`
2. Implement feature-preservation term on top of MSED base:
   - fixed feature metric
   - deterministic modulation policy
   - grayscale-only scope.
3. Add tests:
   - deterministic output hash
   - contrast/edge preservation invariant on canonical edge-heavy fixture
   - grayscale-only guard.
4. Add one diffusion bench case for feature-preserving MSED.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://ira.lib.polyu.edu.hk/bitstream/10397/1524/1/J-JEI-Feature-preserving%20multiscale%20error%20diffusion_04.pdf

---

## PR11 - Green-Noise Multiscale Error Diffusion

### Goal

Add green-noise MSED variant for clustered but artifact-controlled texture.

### Not Already Implemented Check

- No green-noise multiscale method exists in current diffusion exports.

### Files

- `src/diffusion/variable.rs`
- `src/diffusion/mod.rs`
- `src/lib.rs`
- `tests/diffusion.rs`
- `tests/golden.rs`
- `benches/diffusion.rs`
- `README.md`

### Exact Changes

1. Add new API:
   - `green_noise_msed_in_place`
2. Implement deterministic green-noise modulation over multiscale diffusion:
   - fixed spectral target configuration
   - deterministic seed policy.
3. Keep grayscale-only scope in 0.2.0.
4. Add tests:
   - deterministic fixture hash
   - spectral proxy invariant (low-frequency suppression bound)
   - grayscale-only guard.
5. Add one diffusion bench case for green-noise MSED.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://pubmed.ncbi.nlm.nih.gov/20215075/
- https://www.eie.polyu.edu.hk/~enyhchan/J-TIP-Green_noise_digital_halftoning_with_MED.pdf

---

## PR12 - Adaptive Vector Error Diffusion (Color)

### Goal

Add adaptive vector error diffusion for color workflows (RGB/RGBA).

### Not Already Implemented Check

- Current color diffusion uses fixed kernels and per-pixel scalar quantization decisions.
- No adaptive vector-LMS diffusion method exists.

### Files

- `src/diffusion/variable.rs`
- `src/diffusion/mod.rs`
- `src/lib.rs`
- `tests/diffusion.rs`
- `tests/golden.rs`
- `benches/diffusion.rs`
- `README.md`

### Exact Changes

1. Add new API:
   - `adaptive_vector_error_diffusion_in_place`
2. Implement adaptive coefficient update in vector form:
   - deterministic update schedule
   - bounded coefficient range
   - RGB/RGBA support with preserved alpha lane.
3. Add tests:
   - deterministic output hash
   - coefficient bound/invariant test
   - alpha preservation test for RGBA.
4. Add one diffusion bench case for adaptive vector ED.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://pubmed.ncbi.nlm.nih.gov/18282985/
- https://doi.org/10.1109/83.597270

---

## PR13 - Linear Pixel Shuffling Error Diffusion (LPS-ED)

### Goal

Add LPS traversal as an alternative diffusion path to reduce directional artifacts from raster scanning.

### Not Already Implemented Check

- No LPS traversal strategy exists in current diffusion family.

### Files

- `src/diffusion/variable.rs`
- `src/diffusion/mod.rs`
- `src/lib.rs`
- `tests/diffusion.rs`
- `tests/golden.rs`
- `benches/diffusion.rs`
- `README.md`

### Exact Changes

1. Add new API:
   - `linear_pixel_shuffling_in_place`
2. Implement deterministic LPS traversal generator:
   - full-image permutation with fixed seed and dimensions
   - all-direction diffusion neighborhood based on published method.
3. Scope for 0.2.0:
   - grayscale first; return `UnsupportedFormat` for non-gray.
4. Add tests:
   - deterministic permutation stability test
   - deterministic output hash
   - grayscale-only guard.
5. Add one diffusion bench case for LPS-ED.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://repository.rit.edu/other/391/
- https://www.imaging.org/common/uploaded%20files/pdfs/Papers/2000/PICS-0-81/1625.pdf

---

## PR14 - Model-Based Halftoning Family (MED + LSMB)

### Goal

Add model-based halftoning methods (printer + HVS model) as separate advanced algorithms.

### Not Already Implemented Check

- No model-based MED/LSMB algorithm exists in current exports.

### Files

- `src/dbs.rs`
- `src/lib.rs`
- `tests/advanced.rs`
- `tests/golden.rs`
- `benches/advanced.rs`
- `README.md`

### Exact Changes

1. Add APIs:
   - `model_based_med_in_place`
   - `least_squares_model_based_in_place`
2. Keep deterministic behavior with fixed eye/printer model defaults.
3. Scope for 0.2.0:
   - grayscale-first implementation is acceptable.
4. Add tests:
   - deterministic output hash on canonical fixture
   - objective-improvement regression test vs plain thresholding baseline.
5. Add one advanced bench case for each method.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://pubmed.ncbi.nlm.nih.gov/18282991/
- https://doi.org/10.1117/12.135965
- https://users.eecs.northwestern.edu/~pappas/papers/pappas_neuhoff_tip99.pdf

---

## PR15 - HVS-Optimized Error Diffusion (Kolpatzik-Bouman)

### Goal

Add visually optimized error diffusion filter design as a distinct diffusion method.

### Not Already Implemented Check

- Current diffusion wrappers are fixed historical kernels + variable families.
- No explicit HVS-optimized filter-design method exists.

### Files

- `src/diffusion/variable.rs`
- `src/diffusion/mod.rs`
- `src/lib.rs`
- `tests/diffusion.rs`
- `tests/golden.rs`
- `benches/diffusion.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `hvs_optimized_error_diffusion_in_place`
2. Implement deterministic optimized filter-coefficient set based on published approach.
3. Keep method deterministic with fixed coefficient table in 0.2.0.
4. Add tests:
   - deterministic output hash
   - binary/level invariants by quantization mode.
5. Add one diffusion bench case.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://engineering.purdue.edu/~bouman/publications/pdf/jei1scan.pdf
- https://engineering.purdue.edu/~bouman/publications/pub_doc.html

---

## PR16 - Vector/Semi-Vector Color Error Diffusion

### Goal

Add canonical vector color ED and semi-vector ED as separate color diffusion algorithms.

### Not Already Implemented Check

- No explicit vector-valued color ED implementation is exported today.

### Files

- `src/diffusion/variable.rs`
- `src/diffusion/mod.rs`
- `src/lib.rs`
- `tests/diffusion.rs`
- `tests/golden.rs`
- `benches/diffusion.rs`
- `README.md`

### Exact Changes

1. Add APIs:
   - `vector_error_diffusion_in_place`
   - `semivector_error_diffusion_in_place`
2. Implement deterministic matrix-valued error filtering in color space.
3. Preserve alpha for RGBA.
4. Add tests:
   - deterministic output hash on RGB fixture
   - alpha preservation for RGBA
   - seq reproducibility across runs.
5. Add one diffusion bench case for vector ED.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://pubmed.ncbi.nlm.nih.gov/18255498/
- https://doi.org/10.1109/83.951540
- https://users.ece.utexas.edu/~bevans/papers/2003/colorDiffusion/index.html

---

## PR17 - Hierarchical Error Diffusion (HED)

### Goal

Add hierarchical color error diffusion (HED) as a dedicated method.

### Not Already Implemented Check

- No hierarchical ED method exists in current diffusion exports.

### Files

- `src/diffusion/variable.rs`
- `src/diffusion/mod.rs`
- `src/lib.rs`
- `tests/diffusion.rs`
- `tests/golden.rs`
- `benches/diffusion.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `hierarchical_error_diffusion_in_place`
2. Implement deterministic hierarchical control for overlap/position/color sequencing.
3. Scope:
   - RGB/RGBA primary target.
4. Add tests:
   - deterministic hash
   - no-boundary-artifact regression fixture check
   - alpha preservation for RGBA.
5. Add one diffusion bench case.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://pubmed.ncbi.nlm.nih.gov/19473943/
- https://doi.org/10.1109/TIP.2009.2019778

---

## PR18 - Tone-Dependent Error Diffusion (TDED)

### Goal

Add TDED as a separate variable-coefficient family member (distinct from Ostromoukhov/Zhou-Fang).

### Not Already Implemented Check

- TDED is not currently present by name or implementation.

### Files

- `src/diffusion/variable.rs`
- `src/diffusion/mod.rs`
- `src/lib.rs`
- `tests/diffusion.rs`
- `tests/golden.rs`
- `benches/diffusion.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `tone_dependent_error_diffusion_in_place`
2. Implement deterministic tone-trained coefficient lookup path.
3. Keep grayscale-only scope in first pass.
4. Add tests:
   - deterministic hash
   - coefficient index/bounds test
   - grayscale-only guard.
5. Add one diffusion bench case.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://pubmed.ncbi.nlm.nih.gov/15376941/

---

## PR19 - Structure-Aware Error Diffusion (SAED)

### Goal

Add structure-aware ED to reduce worm artifacts while preserving local detail.

### Not Already Implemented Check

- No structure-aware ED method exists in current diffusion family.

### Files

- `src/diffusion/variable.rs`
- `src/diffusion/mod.rs`
- `src/lib.rs`
- `tests/diffusion.rs`
- `tests/golden.rs`
- `benches/diffusion.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `structure_aware_error_diffusion_in_place`
2. Implement deterministic structure-control term with fixed parameters.
3. Scope:
   - grayscale first for 0.2.0.
4. Add tests:
   - deterministic hash
   - artifact-suppression proxy invariant on structure fixture
   - grayscale-only guard.
5. Add one diffusion bench case.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://perso.liris.cnrs.fr/ostrom/publications/pdf/SIGGRAPH-ASIA09_saed.pdf

---

## PR20 - Adaptive Ordered Dither

### Goal

Add adaptive ordered dithering as a distinct ordered-family method.

### Parallelism Decision

`No` for 0.2.0. Keep first implementation serial to preserve canonical behavior while adaptation heuristics are stabilized.

### Not Already Implemented Check

- No adaptive ordered-dither method exists in current `src/ordered/*`.

### Files

- `src/ordered/adaptive.rs` (new)
- `src/ordered/mod.rs`
- `src/lib.rs`
- `tests/ordered.rs`
- `tests/golden.rs`
- `benches/ordered.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `adaptive_ordered_dither_in_place`
2. Implement deterministic adaptive threshold-map selection in ordered core style.
3. Scope:
   - `Gray`/`Rgb`/`Rgba` support with alpha preservation on `Rgba`.
4. Add tests:
   - deterministic fixture hash
   - output level invariants for `u8`/`u16`/`f32`
   - alpha preservation test on RGBA.
5. Add one ordered benchmark entry.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://doi.org/10.1006/gmip.1996.0414
- https://www.sciencedirect.com/science/article/pii/S1077316996904141

---

## PR21 - Space-Filling Curve Ordered Dither

### Goal

Add ordered dithering driven by deterministic space-filling traversal.

### Parallelism Decision

`No` for 0.2.0. Keep traversal and adaptation strictly serial for canonical reproducibility.

### Not Already Implemented Check

- No space-filling-curve ordered dither method exists in current `src/ordered/*`.

### Files

- `src/ordered/space_filling.rs` (new)
- `src/ordered/mod.rs`
- `src/lib.rs`
- `tests/ordered.rs`
- `tests/golden.rs`
- `benches/ordered.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `space_filling_curve_ordered_dither_in_place`
2. Implement deterministic curve traversal with fixed curve order policy.
3. Reuse ordered quantization core to preserve mode/layout behavior.
4. Add tests:
   - deterministic traversal ordering test
   - deterministic fixture hash
   - quantization invariants for `u8`/`u16`/`f32`.
5. Add one ordered benchmark entry.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://doi.org/10.1016/S0097-8493(98)00043-0
- https://www.sciencedirect.com/science/article/pii/S0097849398000430

---

## PR22 - Ranked Dither (Spatially Adaptive)

### Goal

Add ranked dithering as a separate ordered-family algorithm.

### Parallelism Decision

`No` for 0.2.0. Keep serial until deterministic parity fixtures are established across all sample types.

### Not Already Implemented Check

- No ranked-dither method exists in current `src/ordered/*`.

### Files

- `src/ordered/ranked.rs` (new)
- `src/ordered/mod.rs`
- `src/lib.rs`
- `tests/ordered.rs`
- `tests/golden.rs`
- `benches/ordered.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `ranked_dither_in_place`
2. Implement deterministic rank-map generation/usage consistent with ranked-dither references.
3. Support `Gray`/`Rgb`/`Rgba` with alpha preservation.
4. Add tests:
   - deterministic rank-map check
   - deterministic fixture hash
   - output quantization invariants.
5. Add one ordered benchmark entry.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://www.mayagupta.org/publications/GuptaBowenSPIE07.pdf

---

## PR23 - Image-Based Dither Screens

### Goal

Add image-based dither screens as a dedicated ordered-family method.

### Parallelism Decision

`No` for 0.2.0. Keep serial first pass while screen synthesis is validated.

### Not Already Implemented Check

- No image-based-dither-screen method exists in current `src/ordered/*`.

### Files

- `src/ordered/image_based_screen.rs` (new)
- `src/ordered/mod.rs`
- `src/lib.rs`
- `tests/ordered.rs`
- `tests/golden.rs`
- `benches/ordered.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `image_based_dither_screen_in_place`
2. Implement deterministic screen construction path and ordered application.
3. Reuse shared ordered quantization helpers and layout handling.
4. Add tests:
   - deterministic generated screen check
   - deterministic fixture hash
   - quantization invariants for `u8`/`u16`/`f32`.
5. Add one ordered benchmark entry.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://graphicsinterface.org/wp-content/uploads/gi1999-22.pdf
- https://doi.org/10.20380/GI1999.22

---

## PR24 - Polyomino Ordered Dithering

### Goal

Add polyomino-based dithering for non-periodic ordered structures.

### Parallelism Decision

`No` for 0.2.0. Keep serial first pass while polyomino tiling and ranking are locked.

### Not Already Implemented Check

- No polyomino-based dithering method exists in current codebase.

### Files

- `src/ordered/polyomino.rs` (new)
- `src/ordered/mod.rs`
- `src/lib.rs`
- `tests/ordered.rs`
- `tests/golden.rs`
- `benches/ordered.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `polyomino_ordered_dither_in_place`
2. Implement deterministic polyomino tiling + threshold ranking pipeline.
3. Scope:
   - `Gray` first in 0.2.0, return `UnsupportedFormat` for non-gray in first pass.
4. Add tests:
   - deterministic tiling/rank check
   - deterministic fixture hash
   - grayscale-only guard test.
5. Add one ordered benchmark entry.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://arxiv.org/abs/0812.1647

---

## PR25 - Stochastic Clustered-Dot Dithering

### Goal

Add stochastic clustered-dot screen synthesis/application as a separate method.

### Parallelism Decision

`No` for 0.2.0. Keep serial while large-screen synthesis and ranking determinism are stabilized.

### Not Already Implemented Check

- Current clustered-dot support is fixed-map ordered (`cluster_dot_4x4`, `cluster_dot_8x8`) only.
- No stochastic clustered-dot screen synthesis method exists.

### Files

- `src/ordered/stochastic_cluster.rs` (new)
- `src/ordered/mod.rs`
- `src/lib.rs`
- `tests/ordered.rs`
- `tests/golden.rs`
- `benches/ordered.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `stochastic_clustered_dot_in_place`
2. Implement deterministic screen-dot center placement and threshold renumbering pipeline.
3. Reuse ordered core for final in-place application.
4. Add tests:
   - deterministic generated-screen hash
   - deterministic fixture hash
   - output quantization invariants.
5. Add one ordered benchmark entry.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://perso.liris.cnrs.fr/victor.ostromoukhov/publications/pdf/SPIE99_StochasticClust.pdf
- https://pubmed.ncbi.nlm.nih.gov/18255440/

---

## PR26 - Clustered-Dot Direct Multi-Bit Search

### Goal

Add clustered-dot direct multi-bit search for multitoning workflows.

### Parallelism Decision

`No` for 0.2.0. Keep serial due iterative global optimization state.

### Not Already Implemented Check

- Current advanced family has DBS/LBM/electrostatic only.
- No direct multi-bit search variant exists.

### Files

- `src/dbs.rs`
- `src/lib.rs`
- `tests/advanced.rs`
- `tests/golden.rs`
- `benches/advanced.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `clustered_dot_direct_multibit_search_in_place`
2. Implement deterministic multi-bit objective/update path with fixed initialization policy.
3. Scope:
   - integer grayscale first in 0.2.0.
4. Add tests:
   - deterministic fixture hash
   - monotonic objective-improvement test
   - grayscale/integer guard test.
5. Add one advanced benchmark entry.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://pubmed.ncbi.nlm.nih.gov/28113172/
- https://doi.org/10.1109/TIP.2016.2552723
- https://research.ibm.com/publications/hybrid-halftoning-using-direct-multi-bit-search-dms-screen-algorithm

---

## PR27 - Direct Pattern Control Halftoning

### Goal

Add Neugebauer-primary direct pattern control as a dedicated color halftoning path.

### Parallelism Decision

`No` for 0.2.0. Keep serial due coupled pattern-control decisions.

### Not Already Implemented Check

- No direct pattern control method exists in current codebase.

### Files

- `src/dbs.rs`
- `src/lib.rs`
- `tests/advanced.rs`
- `tests/golden.rs`
- `benches/advanced.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `direct_pattern_control_in_place`
2. Implement deterministic NP-selection and pattern-control loop with fixed policy.
3. Scope:
   - RGB/RGBA first in 0.2.0; preserve alpha for RGBA.
4. Add tests:
   - deterministic fixture hash
   - palette/primary membership invariant
   - alpha preservation for RGBA.
5. Add one advanced benchmark entry.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://pubmed.ncbi.nlm.nih.gov/28613170/
- https://doi.org/10.1109/TIP.2017.2713939
- https://cv.ulichney.com/papers/2017-PARAWACS-IEEE.pdf

---

## PR28 - Hierarchical Colorant DBS (MBVQ-Guided)

### Goal

Add hierarchical colorant-based direct binary search with MBVQ-guided tone handling.

### Parallelism Decision

`No` for 0.2.0. Keep serial due hierarchical constrained optimization dependencies.

### Not Already Implemented Check

- No hierarchical colorant DBS method exists in current advanced family.

### Files

- `src/dbs.rs`
- `src/lib.rs`
- `tests/advanced.rs`
- `tests/golden.rs`
- `benches/advanced.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `hierarchical_colorant_dbs_in_place`
2. Implement deterministic hierarchical group ordering and constrained update path.
3. Scope:
   - RGB first in 0.2.0.
4. Add tests:
   - deterministic fixture hash
   - hierarchy-order determinism test
   - quality-regression check vs baseline colorant DBS fixture.
5. Add one advanced benchmark entry.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://pubmed.ncbi.nlm.nih.gov/20236895/
- https://doi.org/10.1109/TIP.2010.2045690
- https://pubmed.ncbi.nlm.nih.gov/28613170/

---

## PR29 - MBVQ/Neugebauer Color Error Diffusion

### Goal

Add an explicit MBVQ/MBVC + Neugebauer-model color error-diffusion branch as a first-class deterministic color family.

### Parallelism Decision

`No` for 0.2.0. Keep serial due per-pixel coupled color-selection and strict canonical traversal requirements.

### Not Already Implemented Check

- No explicit MBVQ/MBVC or Neugebauer-model color ED API exists in the current diffusion exports.

### Files

- `src/diffusion/variable.rs`
- `src/diffusion/mod.rs`
- `src/lib.rs`
- `tests/diffusion.rs`
- `tests/golden.rs`
- `benches/diffusion.rs`
- `README.md`

### Exact Changes

1. Add APIs:
   - `mbvq_color_error_diffusion_in_place`
   - `neugebauer_color_error_diffusion_in_place`
2. Implement deterministic color-primary selection with MBVQ/MBVC constraints and Neugebauer-model-based color-distance evaluation.
3. Scope:
   - RGB/RGBA in first pass; preserve alpha lane in RGBA.
4. Add tests:
   - deterministic fixture hashes for both APIs
   - MBVQ-set membership invariant test
   - alpha-preservation test for RGBA.
5. Add one diffusion benchmark entry for each API.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://www.mdpi.com/2313-433X/6/4/23
- https://doi.org/10.3390/jimaging6040023
- https://patents.google.com/patent/US5991438A/en
- https://patents.google.com/patent/EP0895408A2/en
- https://users.ece.utexas.edu/~bevans/papers/2003/colorDiffusion/index.html

---

## PR31 - Block Error Diffusion

### Goal

Add block-based error diffusion for controlled dot shape/size behavior.

### Parallelism Decision

`No` for 0.2.0. Keep serial due block-neighborhood dependency and deterministic block ordering.

### Not Already Implemented Check

- No block-error-diffusion method exists in current diffusion exports.

### Files

- `src/diffusion/block.rs` (new)
- `src/diffusion/mod.rs`
- `src/lib.rs`
- `tests/diffusion.rs`
- `tests/golden.rs`
- `benches/diffusion.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `block_error_diffusion_in_place`
2. Implement deterministic block quantization + block error propagation.
3. Scope:
   - grayscale first in 0.2.0.
4. Add tests:
   - deterministic fixture hash
   - block-size invariant tests
   - grayscale-only guard.
5. Add one diffusion benchmark entry.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://doi.org/10.1109/TIP.2005.859776
- https://shiftleft.com/mirrors/www.hpl.hp.com/personal/Niranjan_Damera-Venkata/files/ibc.pdf

---

## PR32 - Multichannel Green-Noise Error Diffusion

### Goal

Add generalized multichannel green-noise-mask diffusion for color workflows.

### Parallelism Decision

`No` for 0.2.0. Keep serial due coupled multichannel state and mask-index determinism.

### Not Already Implemented Check

- No dedicated multichannel green-noise-mask diffusion method exists in current color diffusion exports.

### Files

- `src/diffusion/variable.rs`
- `src/diffusion/mod.rs`
- `src/lib.rs`
- `tests/diffusion.rs`
- `tests/golden.rs`
- `benches/diffusion.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `multichannel_green_noise_error_diffusion_in_place`
2. Implement deterministic multichannel error-filtering with green-noise mask guidance.
3. Scope:
   - RGB/RGBA with alpha preservation.
4. Add tests:
   - deterministic fixture hash
   - color-channel invariants
   - alpha preservation on RGBA.
5. Add one diffusion benchmark entry.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://doi.org/10.1109/83.841537
- https://doi.org/10.1364/JOSAA.16.001575

---

## PR33 - AM/FM Hybrid Halftoning

### Goal

Add AM/FM hybrid halftoning paths with explicit clustered-AM/FM support.

### Parallelism Decision

`No` for 0.2.0. Keep serial due screen-adaptation coupling and deterministic training/runtime mapping.

### Not Already Implemented Check

- No AM/FM hybrid or clustered AM/FM method exists in current ordered/diffusion exports.

### Files

- `src/ordered/am_fm.rs` (new)
- `src/ordered/mod.rs`
- `src/lib.rs`
- `tests/ordered.rs`
- `tests/golden.rs`
- `benches/ordered.rs`
- `README.md`

### Exact Changes

1. Add APIs:
   - `am_fm_hybrid_halftoning_in_place`
   - `clustered_am_fm_halftoning_in_place`
2. Implement deterministic screen design and application policy.
3. Scope:
   - grayscale first in 0.2.0.
4. Add tests:
   - deterministic fixture hashes for both APIs
   - level-invariant tests
   - grayscale-only guards.
5. Add one ordered benchmark entry for each API.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://doi.org/10.1117/12.643690
- https://doi.org/10.2352/ISSN.2169-4451.2004.20.1.art00025_2
- https://dblp.org/db/conf/clrimg/clrimg2006.html

---

## PR34 - Blue-Noise Multitone Dithering

### Goal

Add a dedicated blue-noise multitoning algorithm for multilevel outputs.

### Parallelism Decision

`No` for 0.2.0. Keep serial due multitone state coupling and fixed blue-noise update order.

### Not Already Implemented Check

- No dedicated blue-noise multitone method exists in current ordered/diffusion/advanced exports.

### Files

- `src/ordered/multitone.rs` (new)
- `src/ordered/mod.rs`
- `src/lib.rs`
- `tests/ordered.rs`
- `tests/golden.rs`
- `benches/ordered.rs`
- `README.md`

### Exact Changes

1. Add API:
   - `blue_noise_multitone_dither_in_place`
2. Implement deterministic multitone assignment with blue-noise guidance.
3. Scope:
   - grayscale first in 0.2.0.
4. Add tests:
   - deterministic fixture hash
   - multilevel occupancy invariant
   - grayscale-only guard.
5. Add one ordered benchmark entry.

### Validation Commands

```bash
cargo fmt --all
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo test --workspace --all-features --lib --tests --examples
cargo bench --workspace --all-features --no-run
```

### Sources (https)

- https://doi.org/10.1109/TIP.2008.926145
- https://www.eecis.udel.edu/~arce/files/Publications/5-Multitone.pdf

---

## Recommended Merge Order

1. PR00 (module-first public API cleanup)
2. PR01 (image LumaA support gap)
3. PR04 (remaining panic-hardening)
4. PR03 (remaining API deprecations)
5. PR02 (Yliluoma-only parallel API)
6. PR05 (remaining CI feature-matrix coverage)
7. PR06 (remaining bench/golden delta)
8. PR13 (LPS error diffusion)
9. CAPR-A (ordered adaptive/traversal suite: PR20+PR21+PR22)
10. CAPR-B (ordered screen-synthesis suite: PR07+PR23+PR25+PR24)
11. CAPR-H (optimized dot diffusion: PR08)
12. CAPR-C (multiscale diffusion suite: PR09+PR10+PR11)
13. CAPR-D (color/vector diffusion suite: PR12+PR16+PR17)
14. CAPR-E (grayscale quality diffusion suite: PR15+PR18+PR19)
15. CAPR-I (MBVQ/Neugebauer color ED branch: PR29)
16. CAPR-J (block/mask/multitone suite: PR31+PR32+PR33+PR34)
17. CAPR-F (search/model advanced suite: PR14+PR26+PR28)
18. CAPR-G (direct pattern control: PR27)