light: the SHADOW knob rides half its anchor, so a lift stops drawing the band above it flat — a waterfall's spray came back at 0.10 of its own contrast, 0.55 now

docker/frontend/shared/utils/toneShader.ts

@@ -32,7 +32,11 @@ import { HSL_BANDS, hslBandGaps, isMonochromeBase } from './colorUtils';
 // measurement is monotone for every combination of the four at full deflection.
 // A knob moves its anchor by a quarter of the ramp, so +10 BLACKS puts the toe
 // on 0.25 and -10 WHITES rolls the head down to 0.75: the reach a tonal range
-// slider has in the program this layout copies, without the inversion.
+// slider has in the program this layout copies, without the inversion. SHADOW is
+// the one knob held to half of that, because the knot it moves is the HEAD of
+// the quarter above it and not an end of the ramp: a band cannot be lifted at
+// its head and keep its slope at the same time, so the knob's travel is what has
+// to give — see the measured note on a1.
 //
 // WHITE and BLACK are not the per-channel toe and shoulder they were on the WB
 // tab any more. The doc puts the two points on the ends of the SAME ramp as the
@@ -103,9 +107,12 @@ const BAND_BLOCK = hslBandGaps()
 
 // How far a tonal-range knob moves its own knot, in ramp units. A quarter is
 // the reach the program this layout copies gives a slider: at full deflection
-// the four together can put the toe on the midpoint, the head on it, or either
-// end on the quarter next to it — and never past, because each knot is clamped
-// inside the one before it.
+// the toe can reach the quarter above it and the head can be rolled onto it —
+// and never past, because each knot is clamped inside the one after it.
+//
+// SHADOW is the one knob that moves HALF of it. The knot it owns is the HEAD of
+// the 0.25..0.50 quarter, so a unit of lift is a unit of slope that quarter
+// loses, and at a whole quarter the band is drawn flat — see the note on a1.
 export const TONE_ANCHOR = 0.25;
 
 // The tone and exposure maths, in ONE copy, because two passes ask it: the
@@ -125,8 +132,9 @@ float lin(float e0, float e1, float x) {
   return clamp((x - e0) / (e1 - e0), 0.0, 1.0);
 }
 // The ramp the pixel is rebuilt through. Knots on 0.00, 0.25, 0.50, 0.75 and
-// 1.00; a knob moves the knot it owns by TONE_ANCHOR of the ramp, and each knot
-// is held inside the one before it so the five can never cross. 0.50 is fixed:
+// 1.00; a knob moves the knot it owns by TONE_ANCHOR of the ramp — SHADOW by
+// half of that, its knot being the head of a band — and each knot is held inside
+// the one after it so the five can never cross. 0.50 is fixed:
 // it is the one point all four sliders leave alone, which is what keeps a
 // mid-grey a mid-grey while the ends move around it. Straight between the knots,
 // so every knob on zero is exactly the identity (see the note at the head of
@@ -186,7 +194,19 @@ vec3 lightMove(vec3 c, float t, float o) {
 vec3 toneRamp(vec3 c, float t, float bl, float sh, float hl, float wh, float dr) {
   float a4 = 1.0 + ${TONE_ANCHOR} * wh - dr * 0.18;
   float a3 = clamp(0.75 + ${TONE_ANCHOR} * hl - dr * 0.09, 0.5, a4);
-  float a1 = clamp(0.25 + ${TONE_ANCHOR} * sh + dr * 0.06, 0.0, 0.5);
+  // SHADOW rides HALF the anchor, and that is a measured ceiling rather than a
+  // taste. a1 is the HEAD of the quarter above it, so the band 0.25..0.50 pays
+  // in slope for every unit this knot rises — the slope is (0.5 - a1) / 0.25 —
+  // and that band is where a waterfall's spray and a sunlit rock sit. At the
+  // whole anchor the knot lands ON the midpoint and draws the band flat: on a
+  // real frame (DSCF1701, misty valley, 21% of its pixels in the band) SHADOW
+  // +90 came back with 0.10 of the band's own spread and a mean of 0.392 where
+  // it was 0.489 — the milky white sheet the knob was reported for, bright areas
+  // with their contrast gone. At half: 0.55 of the spread, mean 0.441, and the
+  // toe still opens at 1.45x. Half also keeps the knob smooth over its whole
+  // travel — a clamp alone would pin it from +50 on and leave the top of the
+  // slider dead — which is why the RATE is halved and not just the ceiling.
+  float a1 = clamp(0.25 + ${TONE_ANCHOR} * 0.5 * sh + dr * 0.06, 0.0, 0.5);
   float a0 = clamp(${TONE_ANCHOR} * bl + dr * 0.12, 0.0, a1);
   float o = mix(a0, a1, lin(0.00, 0.25, t));
   o = mix(o, mix(a1, 0.5, lin(0.25, 0.50, t)), step(0.25, t));
@@ -638,11 +658,17 @@ export interface ToneUniforms {
 // Chrome crushes the shadows hard while muting colour. Those two parts live
 // here instead of in the 4x5 matrix, which cannot move one end of the curve
 // without also moving the other.
+//
+// The `sh` here is written at DOUBLE what the knob's own arithmetic reads, which
+// is not a taste either: SHADOW moves its knot half an anchor per unit (see a1
+// in TONE_MATH_SKSL), so a stock that wants the toe on 0.18 has to ask for -0.56
+// to land it there. The stock's crush is the knot it puts the ramp on; the unit
+// it is written in belongs to the knob, not to the look.
 const FILM_TONE: Partial<Record<BaseFilter, Partial<ToneUniforms>>> = {
-  'classic-chrome': { sh: -0.28 },
+  'classic-chrome': { sh: -0.56 },
   // Classic Vivid is Classic Chrome's sibling — the shadow crush belongs to the
   // stock, not to the matrix rows, so it comes along.
-  'classic-vivid': { sh: -0.28 },
+  'classic-vivid': { sh: -0.56 },
   'classic-neg': { shT: [-0.018, 0.009, 0.013], hlT: [0.024, 0.008, -0.012] },
   // Acros. A black-and-white stock IS its grey ramp, so this entry only shapes
   // the two ENDS and leaves the middle an identity: a smooth shadow toe that
@@ -651,18 +677,19 @@ const FILM_TONE: Partial<Record<BaseFilter, Partial<ToneUniforms>>> = {
   // paper. Mid-tones are between the 0.25 and the 0.75 knots, so they keep
   // every step the matrix handed over — which is what 'deep black' costs in a
   // colour stock and does not have to cost here.
-  // The values move the two end knots of the ramp: -0.12 puts the toe on 0.22
-  // and -0.05 rolls the head to 0.7375 (each is TONE_ANCHOR = 0.25 per unit).
-  monochrome: { sh: -0.12, hl: -0.05 },
+  // The values move the two end knots of the ramp: -0.24 puts the toe on 0.22
+  // and -0.05 rolls the head to 0.7375 (HIGHLIGHT is TONE_ANCHOR per unit, the
+  // doubled SHADOW half of it).
+  monochrome: { sh: -0.24, hl: -0.05 },
   // B&W HIGH CONTRAST. Acros' ramp with both ends pushed hard: a deeper toe
-  // (-0.32 against Acros' -0.12, so 0.17 against 0.22) so the darks reach true
+  // (-0.64 against Acros' -0.24, so 0.17 against 0.22) so the darks reach true
   // black, and a shoulder that LIFTS instead of rolling (-0.05 → +0.26, the
   // head going to 0.815), which is the whites step of the brief. The stretch
   // between the two inner knots (0.25 and 0.75) is still the identity, so the
   // long smooth stretch of the greys survives — that is what keeps a hard push
   // off the posterised look, and the strength the stock needs on the greys is
   // its matrix slope (SIM_CONTRAST_BIAS in colorUtils), not another move here.
-  'mono-high-contrast': { sh: -0.32, hl: 0.26 },
+  'mono-high-contrast': { sh: -0.64, hl: 0.26 },
 };
 
 export function getToneUniforms(adj: ColorAdjustments, baseFilter?: BaseFilter): ToneUniforms {