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docs: record the blend-statistics fix in the handoff

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The near-end section described the rescale in mix_noise as an open question. It now
records the fix and its before/after measurements on SD 1.5 and MiniMax H3: SD 1.5's
first step away from strength 0 falls from 0.32 to 0.03 image towns, H3's from 0.48
to 0.38, with the reason H3 keeps a step. Tables measured before the fix are marked
as such, and the analysis cache bug that briefly corrupted the H3 comparison is noted.

Left to do: the changelog item is done; the legacy migration item notes that the
sampling_mode tooltip still claims seeds reproduce; and a new item records that the
golden suite never injects shader noise at a stage boundary, because its stub sampler
never calls the progress callback.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
Æmotion Studio
2026-09-12 16:07:12 -07:00
co-authored by Claude Opus 5
parent c13e4dc030
commit 049b34d60b
1 changed files with 49 additions and 17 deletions
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HANDOFF.md
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@@ -20,6 +20,7 @@ are recorded on purpose, because they are the obvious-sounding ideas.
| + | Travel modes | Done (`5434791`) — `walk` / `drift` / `jump` |
| + | Presets | Done (`5434791`, tuned `ce4b1ec`) — seven bundles |
| + | The agreed upgrade | Done — generators fill their own channels, `normalize_strength` on, goldens on the standard pipeline, presets write the widgets |
| + | Blend keeps the base noise's statistics | Done (`f44aeb5`) — the road away from strength 0 starts at the seed's own image |
Most new capabilities are optional inputs defaulting to off. **Two are not:**
`travel_mode` defaults to `walk` and `normalize_strength` defaults on. Both are
@@ -459,19 +460,23 @@ spread across the eight is 3.4 dB.
### Left to do
- **CHANGELOG.** There is no entry for `travel_mode`, presets or anything in this
section, and the 2.1.0 entry still documents `decorrelate_channels`, which was
replaced before it shipped.
- ~~CHANGELOG~~ Done: an Unreleased section covers everything since 2.1.0.
- **The migration is now a lie.** `web/sampling_mode_migration.js` still routes
pre-2.0 workflows to `legacy` "so their seeds keep reproducing", but `legacy`
shares the generators, so its output changed too. Drop the migration, or redefine
`legacy` as the old pipeline *structure* and say so in the changelog.
`legacy` as the old pipeline *structure*. The changelog lists it as a known issue;
the `sampling_mode` tooltip still makes the old claim.
- **Re-calibrate the presets** against real prompts at a working resolution: the
noise they were fitted to has changed. `jump` and `stamp` are exempt, being
byte-identical.
- **Widget ordering.** `preset` still reads last; a major version should move it
to the top of the required block.
- Removing legacy mode altogether remains a separate decision.
- **The golden suite never injects shader noise at a stage boundary.** Its stub
sampler (`tests/helpers.py::recorded_sampling`) never calls the progress callback,
and the pipeline applies boundary events only when it does, so the multi-stage
goldens pin the first stage alone. `test_standard_pipeline.py` does cover
boundaries.
### Watch the widget count
@@ -519,7 +524,9 @@ whether latent distance means anything to the eye.
instead produced wrong `jump` numbers in a first pass, since corrected.
Every run is one stage: `domain_warp`, `multiply`, `normalize_strength` on, octaves
2, warp 0.7.
2, warp 0.7. Everything above "Fixed: the blend keeps the base noise's statistics"
was measured before that fix, which left SD 1.5 essentially unchanged from 0.25 up
and brought H3 nearer its seed's image across most of the range.
### SD 1.5
@@ -610,7 +617,7 @@ staying home (image home 0.90, 0.78, 0.89).
Strengths 0.001, 0.05, 0.10, 0.15 and 0.20 on both models, with streets at 0.10. Each
step is the distance between neighbouring strengths, averaged over seeds, in image
towns; latent distances agree.
towns; latent distances agree. Measured before the fix below.
| step | SD 1.5 | H3 |
|---|---|---|
@@ -621,13 +628,12 @@ towns; latent distances agree.
| 0.15 to 0.20 | 0.28 | 0.28 |
| 0.20 to 0.25 | 0.24 | 0.40 |
- **Strength 0 is not the start of the road.** At exactly 0 the base noise reaches the
sampler untouched. Above 0, `mix_noise` first rescales every channel of it to mean 0
and deviation 1, and only then blends. At 0.001 that rescale is the whole change to
the starting noise (on SD 1.5 the shader's part is 0.08, against 1.7 to 4.2 for the
rescale), the result carries no trace of the field, and still the image moves as far
as an ordinary step or further. Some seeds show it as a new picture (SD 1.5 seed 1234
goes from one grayscale man to another); others barely move (seed 4242).
- **Strength 0 was not the start of the road.** At exactly 0 the base noise reaches the
sampler untouched; above 0, `mix_noise` rescaled every channel of it to mean 0 and
deviation 1 before blending. At 0.001 that rescale was the whole change to the
starting noise (on SD 1.5 the shader's part is 0.08, against 1.7 to 4.2 for the
rescale), the result carried no trace of the field, and still the image moved as far
as an ordinary step or further. Fixed below.
- **After that the road moves in hops, not a glide.** Each 0.05 moves a quarter to half
a town on average, and per seed it alternates between near-identical runs and new
pictures. SD 1.5 seed 1234 holds the same portrait from 0.05 to 0.25 (steps 0.11 to
@@ -643,10 +649,36 @@ towns; latent distances agree.
- **Streets at 0.10** move 0.28 to 0.59 image towns on SD 1.5 and 0.37 to 0.73 on H3,
`phase_shift` 1.0 the least on both.
The rescale is worth revisiting. Matching the blend to the base noise's own mean and
deviation, instead of forcing 0 and 1, would keep strength 0 bit-identical to a stock
KSampler, keep the statistics the model receives from ComfyUI, and make the road
continuous from 0. Not done and not tested: it changes every non-zero-strength output.
### Fixed: the blend keeps the base noise's statistics (`f44aeb5`)
`mix_noise` now gives its result the base noise's own per-channel mean and deviation
instead of exactly 0 and 1. Strength 0 is still bit-identical, checked on every seed of
both models, and as strength approaches 0 the result approaches the base. Both models
were re-rendered from 0 to 0.50 with streets at 0.10, and compared with the runs above.
| image towns | SD 1.5 before | SD 1.5 after | H3 before | H3 after |
|---|---|---|---|---|
| starting noise moved at 0.001 | 1.3 to 3.2% | 0.06% | 1.0 to 1.1% | 0.06% |
| image step, 0 to 0.001 | 0.32 | 0.03 | 0.48 | 0.38 |
| far from home at 0.05 | 0.41 | 0.28 | 0.59 | 0.38 |
| far from home at 0.25 | 0.73 | 0.71 | 0.66 | 0.50 |
| far from home at 0.50 | 1.08 | 1.08 | 0.87 | 0.80 |
- **SD 1.5's road now starts at the seed's own image.** Per seed the first step fell to
0.01, 0.07, 0.00 and 0.02, from 0.38, 0.51, 0.09 and 0.29; seed 8888 is the same man
from 0 through 0.25. From 0.25 up it is essentially unchanged.
- **H3's first step shrank but did not vanish**: per seed 0.18, 0.69 and 0.26, from
0.41, 0.60 and 0.44. Its starting noise moves 0.06 per cent at 0.001, which is the
shader's own share, so the pipeline's jump is gone and the rest is H3 responding to a
very small change. Two things inflate it: one middle frame is compared, where a
slightly different hammer timing moves hands a long way, and H3's seeds look alike, so
a town is small.
- **Unchanged on both**: how much of the field reaches the result, and the
seed-dependent hops after the first step.
The first analysis of H3's after-runs silently reused the before-runs' video frames,
because frames were cached by run name for each model. `839ca1f` gives each manifest
its own cache, and the numbers here come from fresh frames.
### What the two models say together