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Commits
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  dtourolleandClaude Opus 5
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ce6458547a |
Develop longer, from the measurements rather than from a contrast slider
Pushing was not a thing to simulate. It was measured data being thrown away: Double-X and 2302 each ship five characteristic curves, one per development time, and this shipped the 6.5-minute column and discarded four. All five now ship and interpolate. The axis is real. Double-X runs 4 to 12 minutes, and across it the average gradient goes 0.472 to 1.034 while Dmax goes 1.19 to 2.56. The control is in stops, because that is what a photographer means, and one stop is a factor of about 1.41 in time. That mapping is checked rather than assumed: against Double-X's own axis it lands within 2% of the 9-minute column for +1, and near 12 minutes for +2, which are the times the datasheet gives for exactly that. There is a test. **Pushing must not recover shadow detail, and this does not.** Across the whole measured range the speed point moves about a third of a stop while the gradient doubles; three stops under mid-grey, density goes from 0.008 to 0.035, which is still nothing. Developing longer multiplies what was already recorded and cannot record what never hit the film. A push built as added exposure or global contrast brightens those shadows instead and looks convincing until someone who shoots film sees it, so that property has a test of its own. Interpolated in *log* time, because development is multiplicative: 4 to 5 minutes is the same amount of push as 9 to 12, and interpolating linearly would bunch the control at one end. Clamped at both ends, because past the published range there is no data and extrapolating a contrast curve invents an emulsion nobody tested. A stock measured at one process ignores the control entirely rather than inventing a curve for it -- Portra 800's pushes are separate *measured* profiles, which is the honest way to offer those. Costs nothing per pixel and changes no shader. The curves are a per-stock table, so the interpolation happens on the CPU at bake time, where choosing a stock and moving its sliders already rebakes. The Vulkan shader is untouched. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> |
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dtourolleandClaude Opus 5
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4b2ee0ac50 |
Count the silver instead of adding noise
An emulsion is a suspension of crystals. Light sensitises some; development
turns a sensitised one opaque, all or nothing. So a patch of film's density
is a *count* of developed grains, and a count of independent yes/no events
has a variance whether or not anyone wanted texture:
mean = D
variance = D * (Dmax - u * D) / N
That expression is the whole feature. It peaks in the middle of the density
range and vanishes at both ends -- clear film has nothing developed to vary,
black film has nothing left to develop -- so grain lives in the midtones as a
consequence rather than as a "midtone bias" slider.
I was wrong earlier that this needs the detail stage. Nothing in it reads a
neighbouring pixel; the only reason to move it was that grain must be fixed in
film space rather than screen space, and that solves itself: N is grains *per
pixel*, so it scales with the film a pixel covers. Zoom out, each pixel
averages more grains, less variance -- correct, with nothing super-sampled and
nothing filtered. It stays in the fused pass.
Grain goes on the density and *before* the dye, which is the physical order
and not cosmetic. Perturbing the finished colour -- what an effect does --
tints highlights wrong, because that noise never passes through the dye.
Crystal habit lives in `rms_granularity`, the number every datasheet
publishes, now a profile field. It measures exactly what differs between a
cubic emulsion and a tabular one: at equal speed, tabular crystals present
more area per unit silver, so the film reads finer. Delta 100 is quoted near 9
where HP5 is near 12, and that gap *is* the habit. Adding a stock whose grain
is its whole reputation is therefore editing one line, not writing a model.
Three things this cost, all of them worth writing down:
- The default granularity is a colour negative's, blue coarsest. Applied to
Tri-X it put *colour* speckle on a black and white photograph. Monochrome
stocks collapse it at parse, where every other per-layer table is already
replicated from the one measured channel.
- Helpers cannot read uniforms. The composer prefixes a uniform with its
operation's id and rewrites references inside a fragment body only;
helpers are shared and deduplicated, so a bare `gn0` names nothing.
`film_lut` already took its size as an argument for this reason, and now
says so.
- The end-to-end test compares the shader against the CPU model, and grain
is stochastic, so that comparison now runs with grain off. Which means a
grain that never left the CPU would look exactly like a passing suite --
hence a second test that grain off is bit-identical, one grain per pixel
moves it, and ten thousand move it less.
Not here, deliberately: no grain slider. The parameters are physical and
`rms_granularity` is the honest place to scale one from, but its range wants
choosing rather than guessing. Nor a film format -- 35 mm is assumed, and
medium format at the same stock is far less grainy per unit of picture.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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dtourolleandClaude Opus 5
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3b5952769b |
Emit floats an f32 can hold, and drop the format! that formats nothing
CI runs cargo fmt --check and clippy -D warnings, and this branch had never been through either. Both would have failed it. The bulk was the generated colour tables: eight significant figures where an f32 carries about 7.2, so the eighth is noise that rounds away at compile time and clippy's excessive_precision says so 109 times over. Fixed in the generator rather than only in the file, so it stays fixed -- and the file is trimmed in place rather than re-derived, because regenerating it needs a colour-science stack that has nothing to do with the defect. The format! in the composer is mine too, from extracting the rendering tail: the braces in it were escaped because the text used to live inside a larger template, and once extracted the escapes are noise and the call formats nothing. Also here, and clearly not mine: an unused import and a shadowed binding in dr-gpu, and an unused import in a test. They are pre-existing -- clippy has been failing on master before this branch existed, on lints like is_multiple_of that arrived with a toolchain rather than with anyone's code. Fixed because CI cannot go green around them, and called out because a merge commit is a bad place to quietly edit someone else's crate. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> |
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dtourolleandClaude Opus 5
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6d18517d28 |
Ship every stock that exists, black and white included
Three profiles was what the first cut needed to prove the model. This is the rest of the open data: 23 camera stocks and 9 papers, which is all of spektrafilm. Black and white was the gap, and it turned out not to be a gap in the data -- it was a gap in where I looked. Upstream's `main` has 28 colour profiles and nothing monochrome; `dev` has three more, and they are Tri-X, Double-X and the 2302 print film they go onto. So the answer to "do we have B&W" was yes all along, and it needed the dev branch rather than a fortnight digitising Ilford's datasheet graphs by eye. Those three are pinned to `dev` per stock; the colour stocks stay on the released branch. A monochrome profile is single-channel -- one emulsion, not three -- and spreading that one layer across all three is exact rather than an approximation: three layers with identical sensitivity and identical curves respond identically, which is what one layer does. The dye is the trap. The renderer *sums* the three layers' contributions, so replicating it unchanged renders every frame three times too dense -- neutrally, and therefore plausibly. A third each reconstructs the single emulsion, and two tests hold both halves: that the densities stay equal, and that they sum to one emulsion and not three. Double-X and 2302 ship five curves apiece, measured at five development times -- 4 to 12 minutes for Double-X. That is push and pull processing as measured data. The standard 6.5 minutes is what ships; the rest is in the upstream file waiting for a control to ask for it. Two stocks are `support: film` and are nevertheless what a negative is printed *onto*: the cine projection films 2383 and 2393, which the Vision3 stocks print to. Filtering the picker on support alone offered a projection stock as something to load in a camera, so it filters on stage, with a test saying so. The picker had to change shape twice over. Chips were right for three stocks and off the edge of a 280px column at twenty-four, and the column that replaced them was a thousand pixels standing between the photographer and every slider below. It is a disclosure now: one row carrying the answer, opened to change it, closed again on choosing. That is the opposite of the argument this panel used to take the lids off its sliders, and deliberately so -- an instrument you compare wants to be visible, and a list you consult once wants to be out of the way. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> |
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dtourolleandClaude Opus 5
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b6a95e1965 |
Simulate a film stock from its measurements, not from someone's grade
FR-DEV-3f asks for look emulation and proposes HaldCLUT import to inherit
the free film-simulation ecosystem. This takes the other road for the
stocks where the measurements exist: run the physics.
A stock here is its manufacturer's own datasheet -- spectral sensitivity,
characteristic curves, dye densities. Light exposes three emulsion layers,
the layers develop to densities, the densities are dyes that absorb, and
what is left is what reaches the eye. A colour negative comes out orange
and upside down because that is what a colour negative is; it becomes a
photograph when a paper profile prints it, with the enlarger's filtration
solved rather than dialled.
What that buys over a LUT is that the parameters stay physical. Opening up
a stop moves the picture along the film's real characteristic curve,
shoulder and all, instead of scaling a number baked at one exposure. The
data cost runs the other way too: a stock is 17 kB of published
measurements where one HaldCLUT is 800 kB of one person's grade.
It looks like it needs a spectral integration per pixel. It does not, and
that is the whole design:
- Exposure is a 3x3 matrix. The reconstructed scene spectrum is linear
in the sRGB triple, so the integral collapses into nine numbers,
exactly -- no approximation.
- The characteristic curve is three 1D functions, sampled exactly.
- Everything after that -- dye absorption, the print through the
negative, the paper, the viewing illuminant, the adaptation -- takes
exactly three numbers in, so it bakes into one 32^3 lookup.
Per pixel: a matrix multiply, three curve taps, one fetch. Splitting the
curve out of the 3D lookup rather than baking one LUT over exposure is
measured, not assumed: the curve carries the sharp shape and the dye
mixing is smooth, so folding them together would need three times the
resolution for the same error. At 32^3 the worst error is 0.003 in linear
sRGB, under one 8-bit code value, and a test says so.
No wgpu dependency, deliberately, and the same isolation argument dr-lens
makes: the model is plain f32 with a documented layout, so every property
worth asserting is asserted on the CPU. Binding it to a texture is dr-gpu's
job and is not done here yet.
The expected values in tests/ came from a Python prototype running against
a different colour-science stack. Agreement to three decimals is evidence
about the model rather than about one implementation of it -- a transposed
matrix or a mispasted observer row would pass every unit test and fail
that one.
Profiles are converted from spektrafilm by Andrea Volpato, CC BY-SA 4.0.
The converter is in the tree and runnable, so what was changed from
upstream is auditable rather than taken on trust; profiles/CHANGELOG.txt
records it, including the one deliberate deviation -- Mallett & Yuksel's
1 kB basis instead of Hanatos's 4 MB table, which costs accuracy at the
gamut edge and saves four megabytes.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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