# Repixelizer

Repixelizer is a standalone Python CLI for images that are doing a pixel art impression instead of actually respecting the grid.

It is aimed at the annoying middle ground: sprites, emblems, and logos that look locally pixelated but fall apart the second you ask them to commit to one lattice like grown-ups.

Instead of pretending this is a resize problem, Repixelizer treats it as lattice inference plus local structure preservation: infer the implied grid, choose real output cells, and snap them back onto a coherent pixel lattice while preserving the source's local adjacency patterns.

## Examples

Repixelizer was built to rescue fake pixel art, but it can also be used to generate pixel art directly from non-pixel source art when the shapes are clean and the local structure is doing something useful.

Rows show the source art, a plain Lanczos downscale to the same target size, and the repixelized result. The bottom row also carries a sword-guard picture-in-picture, because that tiny region is one of the more honest tests of whether the tool is preserving local cell adjacency instead of just getting the vibes approximately correct.

![Repixelizer example comparison](docs/readme-assets/badge-example-sheet.png)

That is the two-headed pitch in one image: force non-pixel art onto a coherent grid, or take AI pixel art that only respects the grid locally and make it commit.

## Current Status

This repo is past the "pile of hopeful heuristics" stage and into "real machine, still experimental."

What exists now:

- lattice inference with CUDA support
- a lean displacement-field optimizer in `src/repixelizer/phase_field.py`
- a source-owned alternate solver in `--reconstruction-mode tile-graph`
- automatic diagnostics, comparisons, and benchmark runs
- a tuning harness for offline parameter sweeps
- metrics that finally care about visible structure instead of only pleasing the lattice accountant

What changed recently:

- the old tray-based optimizer is gone
- `phase-field` is now the default optimizer path
- `source_structure` is reported alongside `source_fidelity`, because the old metric was happily calling better-looking images worse
- the tracked sword-tip blemish on the AI badge has its own focused fixture in `tests/fixtures/real/ai-badge-tip-focus.json`

Current read on the engines:

- `phase-field` is the main line now. It is the best-looking badge result the repo has produced so far, especially on internal structure, even though it still widens the sword-tip stroke a bit too much in the tracked focus crop.
- `tile-graph` is still useful and still very real, but it remains slower and more temperamental on messy badge-scale inputs. Its best full-emblem probe under `artifacts/full-emblem-tile-graph-atomic-v3-cuda/` is still a strong result.

Current weak spots:

- `phase-field` still needs better along-stroke versus across-stroke behavior near tapered contours
- tile-graph cold-build time is still dominated by connected-component labeling / region extraction on large fixtures
- lattice selection is still low-confidence on some ugly generated inputs, so pinned-size iteration remains an important workflow

## Quickstart

```powershell
python -m venv .venv
.venv\Scripts\python -m pip install -e .[dev]
```

Run the optimizer:

```powershell
repixelize input.png --out output.png
repixelize input.png --out output.png --diagnostics-dir diagnostics --device auto
repixelize input.png --out output.png --reconstruction-mode phase-field --diagnostics-dir diagnostics --device auto
repixelize input.png --out output.png --reconstruction-mode tile-graph --diagnostics-dir diagnostics --device cpu
repixelize input.png --out output.png --reconstruction-mode tile-graph --diagnostics-dir diagnostics --device cuda
repixelize input.png --out output.png --reconstruction-mode tile-graph --target-width 126 --target-height 126 --phase-x 0.0 --phase-y -0.2 --device cuda
```

Run the optimizer plus baselines:

```powershell
repixelize compare input.png --out output.png --diagnostics-dir diagnostics
```

## Corpus And Benchmarks

Prepare a local Creative Commons corpus:

```powershell
repixelize prepare-corpus --corpus-dir examples/corpus
```

Run the round-trip benchmark:

```powershell
repixelize benchmark --corpus-dir examples/corpus --out-dir artifacts/benchmark
```

Useful benchmark flags:

- `--profile soft` or `--profile crisp`
- `--case <name>` repeated for a focused slice
- `--limit <n>` for the first `n` matching cases
- `--infer-size` to test automatic size inference
- `--keep-existing` if you explicitly want to preserve an old output directory

By default the benchmark clears its output directory before each run so the artifacts folder stays readable.

## Tuning

Repixelizer includes a black-box tuning loop for longer offline searches over solver weights:

```powershell
repixelize tune --corpus-dir examples/corpus --out-dir artifacts/tuning --profile soft --limit 8
```

This is intentionally a search-based tuner, not gradient descent. The objective depends on discrete argmins, thresholding, and benchmark comparisons, so it is better treated as a repeatable black-box optimization problem.

## Repository Hygiene

This repo is set up to be safe for local experimentation:

- generated outputs under `artifacts/` are ignored
- local corpus payloads under `examples/corpus/originals/` are ignored
- archived raw sprite sheets under `examples/corpus/source-sheets/` are ignored
- generated corpus metadata files are ignored

That keeps benchmark assets, attribution exports, and tuning runs from polluting upstream history while still keeping the code, docs, and corpus layout tracked.

## Repo Layout

- `src/repixelizer`: core package
- `tests`: focused regression tests
- `docs/spec.md`: product and technical spec
- `docs/implementation-plan.md`: working roadmap
- `docs/tile-graph-algorithm-map.md`: detailed tile-graph dataflow and failure-point map
- `docs/lean-optimizer-algorithm-map.md`: map of the live displacement-field optimizer
- `examples/corpus/README.md`: local corpus layout and attribution workflow

Core modules:

- `inference.py`: target size and phase inference
- `phase_field.py`: default displacement-field optimizer
- `tile_graph.py`: source-owned alternate reconstruction path
- `metrics.py`: fidelity, adjacency, and motif metrics
- `benchmark.py`: corpus benchmark runner
- `tuning.py`: black-box hyperparameter search harness
- `synthetic.py`: facsimile generation for tests and benchmarks

## Validation

Run the focused test suite with:

```powershell
.venv\Scripts\python -m pytest -q
```

## Regenerating README Assets

The README comparison sheet is generated from repo-tracked fixtures, not from random artifacts left lying around:

```powershell
.venv\Scripts\python scripts\generate_readme_previews.py --vector-input tests\fixtures\real\ai-badge-vector.png --ai-input tests\fixtures\real\ai-badge-cleaned.png --out-sheet docs\readme-assets\badge-example-sheet.png --out-guard-crop docs\readme-assets\guard-right-crop-comparison.png --scratch-dir artifacts\readme-build --device cpu
```

That regenerates the README sheet, the standalone sword-guard closeup strip, and scratch outputs under `artifacts/readme-build/` so you can inspect the actual low-res results used to build the docs sample.

## Diagnostic Closeups

For docs or regression notes, you can generate reproducible source/output closeups from output-grid cell coordinates with:

```powershell
.venv\Scripts\python scripts\render_focus_crop.py --input tests\fixtures\real\ai-badge-cleaned.png --out docs\readme-assets\guard-right-crop-source-final.png --cell-bbox 73 20 107 44 --panels source,final --scale 16 --steps 48 --device cpu
```

If you want the full internal state sheet instead of the docs-facing comparison:

```powershell
.venv\Scripts\python scripts\render_focus_crop.py --input tests\fixtures\real\ai-badge-cleaned.png --out docs\readme-assets\guard-right-crop-states.png --cell-bbox 73 20 107 44 --panels source,initial,final --scale 16 --steps 48 --device cpu
```

Notes:
- `--cell-bbox` is in output-grid coordinates, not source-image pixels.
- The script maps that region back to the matching source crop automatically.
- `--device cpu` is the polite choice for docs generation if you do not want to stress the GPU for a tiny crop.

## Notes

- The local corpus is optional; the codebase is still usable without it.
- The benchmark and tuning commands are designed for iterative local work, not for shipping generated artifacts in git.
- Palette enforcement is optional and can be left off for unconstrained recovery runs.