light: the HIGHLIGHT knob rides half its anchor too, so a lift stops drawing a cloud to paper and a pull stops flattening the quarter under it — the top quarter came back at 0.26x of its own contrast, 0.62x now

docker/frontend/shared/utils/toneShader.ts

@@ -110,9 +110,9 @@ const BAND_BLOCK = hslBandGaps()
 // 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.
+// SHADOW and HIGHLIGHT move HALF of it. The knots they own (a1, a3) are the HEAD
+// of a 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 notes on a1 and a3.
 export const TONE_ANCHOR = 0.25;
 
 // The tone and exposure maths, in ONE copy, because two passes ask it: the
@@ -132,9 +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 — 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:
+// 1.00; a knob moves the knot it owns by TONE_ANCHOR of the ramp — SHADOW and
+// HIGHLIGHT by half of that, their knots being the heads of bands — 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
@@ -193,7 +193,15 @@ 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);
+  // HIGHLIGHT rides half the anchor for the reason a1 below does, and this knot
+  // is the worse of the two: a3 is the HEAD of the 0.75..1.00 quarter, so a unit
+  // of lift is a unit of slope the top quarter loses — at the whole anchor +100
+  // lands the knot ON a4 and the quarter is drawn flat (a cloud to paper, the
+  // quarter slopes 1.00 1.00 2.00 0.00), and the same knob the other way pins it
+  // on 0.50 and flattens the quarter BELOW it instead (1.00 1.00 0.00 2.00).
+  // Half draws neither: every quarter keeps between 0.5 and 1.5 of its own slope
+  // over the whole travel, and the head still rolls from 0.625 to 0.875.
+  float a3 = clamp(0.75 + ${TONE_ANCHOR} * 0.5 * hl - dr * 0.09, 0.5, a4);
   // 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 —
@@ -659,11 +667,12 @@ export interface ToneUniforms {
 // 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.
+// The `sh` and `hl` here are written at DOUBLE what the knob's own arithmetic
+// reads, which is not a taste either: SHADOW and HIGHLIGHT each move their knot
+// half an anchor per unit (see a1 and a3 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: -0.56 },
   // Classic Vivid is Classic Chrome's sibling — the shadow crush belongs to the
@@ -678,18 +687,18 @@ const FILM_TONE: Partial<Record<BaseFilter, Partial<ToneUniforms>>> = {
   // 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: -0.24 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 },
+  // and -0.10 rolls the head to 0.7375 (both SHADOW and HIGHLIGHT ride HALF an
+  // anchor per unit, so a stock written against the knot asks for double).
+  monochrome: { sh: -0.24, hl: -0.10 },
   // B&W HIGH CONTRAST. Acros' ramp with both ends pushed hard: a deeper toe
   // (-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
+  // black, and a shoulder that LIFTS instead of rolling (-0.10 → +0.52, 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: -0.64, hl: 0.26 },
+  'mono-high-contrast': { sh: -0.64, hl: 0.52 },
 };
 
 export function getToneUniforms(adj: ColorAdjustments, baseFilter?: BaseFilter): ToneUniforms {