repixelizer/docs/implementation-plan.md

Repixelizer Implementation Plan

Current state

The project is bootstrapped and runnable as a standalone Python repo.

Implemented:

• package metadata and editable install
• CLI entrypoint with run and compare modes
• lattice/phase inference with coherence scoring plus source-period prior
• source-image structural analysis
• PyTorch-based continuous UV-field optimization
• discrete cleanup on the output grid
• optional palette loading and quantization modes
• compare mode with naive and diffusion baselines
• diagnostics writing
• synthetic test fixtures and automated tests

Verified:

• local editable install in a dedicated venv
• full test suite currently passing
• compare-mode smoke run against a real emblem image

What is still provisional

The current implementation should be treated as a strong experimental baseline, not a final algorithm.

The most provisional areas are:

• lattice inference on real, messy generated imagery
• the exact loss weighting in the continuous stage
• the strength and shape of discrete cleanup heuristics
• compare-mode metrics as a proxy for actual visual quality

Near-term priorities

High-value regression cases

AI badge emblem with baked checkerboard background

This locally generated AI badge has become a useful stress case because it fails in a very specific, repeatable way.

Why it is useful:

• the global target size is broadly plausible, so the failure is not just "picked the wrong lattice"
• the lower sword-tip region contains sharp single-pixel and near-single-pixel features at multiple orientations
• those features are exactly the kind of local adjacency pattern Repixelizer is supposed to preserve

Current failure modes:

• the right side of the sword tip develops a wobbling outline instead of a smooth taper
• thin oblique outline features around the tip get collapsed into mushy transitions
• local cell assignments near the tip look inconsistent even when the overall badge size feels right
• the right-hand guard wing loses short dark-light-dark adjacency motifs and collapses into a chunky gold slab
• some guard closeups look nearly identical across snap, relaxed, and final, which suggests the wrong local motif is often chosen before later refinement even starts

Important note:

• the checkerboard is baked into the source image, not transparency
• when projected onto a 122x122 output grid it aliases into a visible 2-3-2 cadence
• that 2-3-2 background rhythm is expected from resampling the background pattern and should not be mistaken for proof that the inferred lattice itself is varying in size
• it is still a problem, because the background is treated as real source structure and can contaminate local scoring near the blade

What future work should improve here:

• better weighting of thin local outline/motif preservation relative to high-contrast cell transitions
• some form of coordinated local relaxation so nearby cells can move together toward a globally better contour
• optional background suppression or de-weighting when a baked checkerboard is clearly not semantic content

Current optimizer diagnosis:

• a lot of the so-called source_* terms in the solver are still measured against the smoothed representative lattice, not raw source-side candidate evidence
• that means the optimizer often "preserves" a softened, already-collapsed interpretation of the source instead of the sharper local adjacency patterns we actually care about
• snap is still especially guilty here: its base match and neighbor deltas are dominated by the representative lattice, so the wrong local motif can be locked in before relaxation or hard refinement even starts
• relaxation can often descend to a much lower expected energy basin, but the hardening/refine handoff then projects that soft solution back into a worse discrete assignment
• diagonal structure is also underrepresented in the final structure score, which is a bad fit for curved one-pixel outlines and hooks

Most likely next fixes:

• derive a sharper per-cell source reference from actual sampled source patches instead of using the soft representative as the only "source truth"
• point snap, relaxation, and structure-scoring source terms at that sharper source reference
• harden the relaxed solution more honestly by considering the relaxed mode assignment, not just a per-cell handoff argmin
• include diagonal boundary agreement in the final structure score so oblique tiny features matter earlier

Repository fixtures:

• tests/fixtures/real/ai-badge-cleaned.png is the manually cleaned transparent version of the same emblem
• tests/fixtures/real/ai-badge-cleaned.json records why it matters
• use the cleaned fixture when isolating lattice and contour failures from background-removal failures
• scripts/render_focus_crop.py generates reproducible docs/debug closeups from output-grid cell coordinates
• the current docs-facing guard crop uses --cell-bbox 73 20 107 44

1. Build a real benchmark corpus

Add curated real-world cases, not just synthetic ones:

• emblems and logos with transparency
• icons with strong outlines
• simple sprite-like figures
• examples that are known to fail naive resize-and-dither

Each case should include:

• source image
• expected target size or plausible size range
• short notes on known failure modes

2. Improve lattice inference

The current inference is workable but still heuristic.

Next improvements should focus on:

• better periodicity detection for noisy or partially aligned images
• stronger penalties against oversized candidate grids
• confidence calibration that reflects ambiguity more honestly

3. Strengthen the discrete cleanup stage

Current cleanup is local and generic.

Next version should add:

• stronger outline continuity rules
• better preservation of highlight bands
• better handling of metallic or gem-like materials
• smarter alpha-edge cleanup for transparent icons

4. Make compare mode more trustworthy

The current metrics are useful but still internal.

Next work should:

• expand score breakdowns
• validate whether the metrics correlate with actual human preference
• make it easier to compare runs across parameter sweeps

Suggested next milestones

Milestone 1: Real-image evaluation harness

• add curated real-image fixtures
• add golden metadata for expected target-size ranges
• add a repeatable batch runner
• emit one summary table per corpus run

Milestone 2: Solver tuning pass

• tune continuous-stage loss weights against the benchmark corpus
• test more robust anti-speckle and cluster-preservation behavior
• reduce cases where the solver underperforms the naive baseline

Milestone 3: Better cleanup heuristics

• add contour-aware cleanup
• add material-sensitive smoothing for highlights and trim
• reduce the number of visually good-but-metric-weak outputs

Milestone 4: Human-in-the-loop v2 planning

Only after the automatic baseline is strong:

• explore optional region hints
• evaluate a minimal GUI or notebook layer
• consider multi-frame support

Risks

• The solver can still produce outputs that score well but feel over-smoothed.
• Real generated images may contain multiple inconsistent local lattice cues.
• Continuous optimization is flexible, but easy to overfit to the reconstruction term.
• Metrics that reward coherence can accidentally reward blandness if not balanced carefully.

Assumptions

• Single-image quality matters more than batch throughput in the current phase.
• Palette constraints are optional and should stay optional.
• The project is better served by improving automatic behavior first than by rushing into manual tooling.
• Python plus PyTorch remains the right stack for the current research/prototyping phase.