dtourolle
db7b84795c
Every point operation ran in camera RGB and the camera matrix came after them all, against the order ARCH §5.2 draws. So `luminance()` applied Rec.709 weights to a body's own primaries, a band in the colour mixer was a different hue on every make of sensor, and the vibrance skin guard tested channel order in a space where skin does not have one. Operations now declare a `Stage`. White balance is the only camera-stage node — its multipliers scale the sensor's channels, and after a matrix that mixes them the same numbers are a different correction — and says so with `stage: camera` in its YAML, a key both the build-time generator and the load-time declared op read. The composer emits the camera nodes, then the matrix, then the rest, each group in graph order; an empty chain still gets the matrix. Film simulation stops converting out of camera space itself, since it is now handed working-space colour like every other scene node. The base curve stays where it was, after the operations, and so now acts on working-space colour; the next commit replaces it (D19).
122 lines
4.8 KiB
YAML
122 lines
4.8 KiB
YAML
id: white_balance
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label: op.white_balance
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order: 10
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attributes: [colour]
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doc: |
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White balance — temperature and tint, relative to as-shot.
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Expressed as an offset from what the camera chose rather than an absolute
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kelvin value. Neutral means "as shot", so the control starts where the
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image already is and a reset returns there. An absolute scale would make
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the neutral position depend on the file, which is exactly the confusion
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Lightroom's temperature slider creates on non-raw files.
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The as-shot multipliers themselves are applied by the composer's preamble
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rather than here — every image has them even when this operation is
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neutral, so they cannot live in a fragment that vanishes at neutral.
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placement: |
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First. It is a correction to how the scene was captured, and every tonal
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operation after it should act on a correctly balanced image.
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# In camera RGB, ahead of the camera matrix, and the only node there (D19).
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# Its multipliers scale the sensor's own channels — that is what the as-shot
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# ones are, and what the picker solves for — and a matrix that mixes the
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# channels, which is every body's, would turn the same numbers into a
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# different correction once it had run.
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stage: camera
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params:
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temperature:
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label: param.temperature
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kind: amount
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doc: |
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Warmer is positive, matching every other raw developer: dragging right
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makes the image warmer, even though that means *lowering* the colour
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temperature being corrected for.
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tint:
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label: param.tint
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kind: amount
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# An eyedropper, where the frontend has a canvas to hang one on.
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#
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# Sampling a neutral is the first move of the global tonal pass — every colour
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# judgement afterwards is measured against where the grey was put — and it is
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# a thing you do by pointing at the photograph, not by guessing at two sliders
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# until a wall stops looking green.
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#
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# A *hint*, on the usual terms: the two parameters below stay ordinary
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# addressable scalars, and a frontend with nowhere to host a sampler renders
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# them as the sliders they already were. This one is additive rather than a
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# replacement — the picker writes temperature and tint and the photographer
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# still nudges them afterwards — which is a difference the frontend draws for
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# itself; nothing here has to say it.
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#
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# The order matters and is the widget kind's own contract: the first parameter
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# trades red against blue, the second green against magenta.
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presentation:
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widgets: [white_point]
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params: [temperature, tint]
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demand:
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# A neutral is a point on the picture, so both axes at once.
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two_dimensional: true
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# Deliberately false. A grey card, a cloud, a white wall — the things
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# worth sampling are large, and FR-UI-7 grows the hit region to the
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# modality in any case, so a thumb is as workable as a mouse.
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precise_pointing: false
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# Temperature trades red against blue; tint trades green against magenta.
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# Both are scaled so the full range is a strong but not destructive
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# correction: ±0.5 in log2 at the extremes — half a stop of channel shift,
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# which covers ordinary illuminant error without letting the slider blow a
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# channel on its own.
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uniforms:
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mul_r: exp2(temperature / 100 * 0.5)
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mul_g:
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value: exp2(-(tint / 100 * 0.5))
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doc: |
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Green is held at unity by temperature, so the control does not double as
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an exposure slider — green carries most of the luminance.
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mul_b:
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value: exp2(-(temperature / 100 * 0.5))
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doc: Blue moves opposite red, so a neutral grey stays grey as the control moves.
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wgsl: |
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c = c * vec3<f32>(mul_r, mul_g, mul_b);
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tests:
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- name: neutral_is_as_shot
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expect: { mul_r: 1.0, mul_g: 1.0, mul_b: 1.0 }
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expect_active: false
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- name: warming_raises_red_and_lowers_blue
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set: { temperature: 100 }
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expect: { mul_r: 1.4142135, mul_b: 0.70710677 }
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- name: temperature_leaves_green_alone
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why: |
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Otherwise the control doubles as an exposure slider, because green
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carries most of the luminance.
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set: { temperature: 100 }
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expect: { mul_g: 1.0 }
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- name: tint_moves_green_against_magenta
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why: Positive tint reduces green, and must not touch red or blue.
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set: { tint: 100 }
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expect: { mul_g: 0.70710677, mul_r: 1.0, mul_b: 1.0 }
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- name: cooling_is_the_inverse_of_warming
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why: |
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Warming by n then cooling by n must return to neutral, so the two
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directions have to be exact reciprocals rather than merely similar.
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set: { temperature: -100 }
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expect: { mul_r: 0.70710677, mul_b: 1.4142135 }
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- name: the_extremes_stay_within_half_a_stop
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why: |
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A white balance control that can blow a channel by itself is a trap;
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correction belongs in a range where highlights survive.
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set: { temperature: 100, tint: 100 }
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expect_range: { mul_r: [0.70, 1.42], mul_g: [0.70, 1.42], mul_b: [0.70, 1.42] }
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