optimalbyteeandClaude Opus 5.5
6ae2a8498c
Radial Blur prepares its sample transforms once per filter (blur::radial::Plan) and shares them across output tiles, reading each bilinear tap once with channels kept together. Output is identical to the previous sampler at Draft, Good and Best, across colour models and depths (tests compare against the unchanged reference path); a failed table allocation falls back to that sampler. Measured on 24 MP RGBA8, Good, amount 1: Spin 66.1 -> 16.4 s, Zoom 19.2 -> 5.4 s (bench_radial example, docs/radial-blur-performance.md). Co-Authored-By: Claude Opus 5.5 <[email protected]>
3.0 KiB
Radial Blur sampler optimization
The tiled filter prepares Spin rotations or Zoom scales once per operation and reuses them across output tiles. Bilinear taps load all channels together, with specialized loops for one through five channels and a generic fallback. Rayon continues to parallelize output tiles on native builds.
Draft, Good and Best keep upstream's 64, 256 and 4096 interval ceilings, sample positions, transparent edges and alpha arithmetic. The positive-alpha unpremultiply/premultiply sequence is retained to preserve floating-point rounding. Tests compare against the unchanged upstream sampler at large radii across Gray, RGB, CMYK and Lab, with and without alpha, at U8, U16 and F32 depths. Selection blending and unusual float alpha are covered as well.
Only interval counts reachable within the output area are prepared; small Best images avoid allocating/preparing the full roughly 64 MiB transform table. Preparation and output allocations use checked sizes and fallible reservation. If the optional optimization cannot prepare its tables, the existing sampler runs instead. Cancellation is checked during preparation and within output tiles.
This revision adds no source-size rejection: it retains upstream's shared normalized source read and therefore still requires memory proportional to source size. It does not claim bounded source memory or unlimited physical capacity. The polar approximation and background preview scheduler are separate work.
Local comparison (2026-10-09)
| Method | Upstream | Optimized | Speedup | Output |
|---|---|---|---|---|
| Spin | 66.10 s | 16.43 s | 4.02× | Exact match |
| Zoom | 19.19 s | 5.35 s | 3.59× | Exact match |
Baseline: current upstream sampler at main 578bc905, through kernel, using
the same shared source read, 256px output tiles, 256 MiB result batches, surface
writeback and pruning as the tiled filter. Optimized: apply_in.
The benchmark's baseline wrapper covers full-canvas, unselected filtering only;
selection behavior is checked separately in tests.
Machine: Intel Core i7-9750H (6 cores / 12 logical workers), Linux, Rust 1.98.1, release profile with opt-level 3, thin LTO and one codegen unit. Source: deterministic textured RGBA8 with transparent pixels, 6000×4000 (24 MP). Good quality, amount 1, center (0.5, 0.5), 12 Rayon workers. One paired run per method, upstream first, after a small untimed warmup. Entire filtering calls are timed; fixture generation and exact comparison of every output tile are outside the timer.
These are single local measurements, not a cross-machine baseline or an amount-100 performance claim. The lower amount keeps this review benchmark bounded on the local laptop. Quality ceilings are verified separately at large radii. The example defaults to three alternating-order runs and amount 100 for longer measurements. Historical handoff polar/default timings do not describe this output-preserving implementation.
cargo run --release -j 12 -p photocraft-algo --example bench_radial -- 6000 4000 1 1