Upscaled snapshots show a regular grain on flat colours #932

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opened 2026-10-22 03:12:20 +00:00 by sky_line · 1 comment

sky_line commented

2026-10-22 03:12:20 +00:00

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A user reports a fine, fairly regular grainy pattern on solid-colour areas of snapshots larger than the window (the live jittered accumulation path from #873).

Likely causes

Frozen noise seeds. While a live shot accumulates, mTaaFrame is held so the live view resumes cleanly. Any per-frame noise seeded from it (dithers, stochastic picks, sample rotations) repeats in every sample, so averaging cannot remove it.
Few samples per pixel. Each sample is a raw jittered frame (TAA / FSR resolve skipped), so the noise TAA normally hides (GTAO, soft RT shadow rays, stochastic projector picks, fog / god-ray / alpha dithers) stays in, and about 4 samples per output pixel only roughly halves it.
Coarse shading. Adaptive VRS (on by default from 1440p) shades low-contrast areas at 2x2; jittered samples over those blocks leave a regular pattern.

Plan

Give every noise source its own per-sample seed during a shot (or advance a dedicated snapshot seed) without disturbing the live view's sequence.
Force full-rate shading for snapshot sample frames.
Revisit the minimum samples per output pixel / RenderSnapshotTemporalFrames defaults.
Verify with a snapshot of a flat-colour wall at 2x and 4x the window, against the offscreen renderer (RenderSnapshotOffscreen 1).

Tiled rendering was considered and set aside: per-tile warm-up for the temporal passes, guard bands for screen-space effects and whole-image post would be a much larger change than fixing the samples.

A user reports a fine, fairly regular grainy pattern on solid-colour areas of snapshots larger than the window (the live jittered accumulation path from #873). ## Likely causes 1. **Frozen noise seeds.** While a live shot accumulates, `mTaaFrame` is held so the live view resumes cleanly. Any per-frame noise seeded from it (dithers, stochastic picks, sample rotations) repeats in every sample, so averaging cannot remove it. 2. **Few samples per pixel.** Each sample is a raw jittered frame (TAA / FSR resolve skipped), so the noise TAA normally hides (GTAO, soft RT shadow rays, stochastic projector picks, fog / god-ray / alpha dithers) stays in, and about 4 samples per output pixel only roughly halves it. 3. **Coarse shading.** Adaptive VRS (on by default from 1440p) shades low-contrast areas at 2x2; jittered samples over those blocks leave a regular pattern. ## Plan - Give every noise source its own per-sample seed during a shot (or advance a dedicated snapshot seed) without disturbing the live view's sequence. - Force full-rate shading for snapshot sample frames. - Revisit the minimum samples per output pixel / RenderSnapshotTemporalFrames defaults. - Verify with a snapshot of a flat-colour wall at 2x and 4x the window, against the offscreen renderer (RenderSnapshotOffscreen 1). Tiled rendering was considered and set aside: per-tile warm-up for the temporal passes, guard bands for screen-space effects and whole-image post would be a much larger change than fixing the samples.

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2026-10-22 03:12:20 +00:00

sky_line added this to the Slipstream project

2026-10-22 03:12:20 +00:00

sky_line referenced this issue from a commit

2026-10-22 08:20:13 +00:00

#932: upscaled snapshots -- per-sample noise seeds, dither once, full-rate shading

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