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
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@@ -16,13 +16,15 @@
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// THE TONE PASS builds the luma a new ramp instead. The four knobs
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// (HIGHLIGHT, SHADOW, WHITE, BLACK) are the four zones of the tone-mapping doc —
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// one tent each, one per quarter of the ramp — and each knob moves the knot it
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// owns by TONE_ANCHOR of the ramp, held inside the knot before it. The 0.50
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// midpoint is the one value all four leave where it was.
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// owns by TONE_ANCHOR of the ramp, held inside the knot before it; SHADOW, whose
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// knot is the head of the band above it rather than an end of the ramp, moves
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// half that. The 0.50 midpoint is the one value all four leave where it was.
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//
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// Both are SkSL, so the SHAPE is pinned on the source; the arithmetic is then
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// checked against the source's own constants, and the ramp re-run here as a twin
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// so monotonicity, the neutral identity and the partition of the four masks are
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// checked rather than asserted in a comment.
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// so monotonicity, the neutral identity, the partition of the four masks and the
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// slope SHADOW leaves the band above it are checked rather than asserted in a
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// comment.
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//
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// node scripts/highlight-knee-check.mjs
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import assert from 'node:assert/strict';
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@@ -83,7 +85,7 @@ assert.match(sksl, /float hlMask = clamp\(smoothstep\(0\.50, 0\.75, t\) - whMask
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// knots next to them.
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assert.match(sksl, /float a4 = 1\.0 \+ 0\.25 \* wh - dr \* 0\.18;/);
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assert.match(sksl, /float a3 = clamp\(0\.75 \+ 0\.25 \* hl - dr \* 0\.09, 0\.5, a4\);/);
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assert.match(sksl, /float a1 = clamp\(0\.25 \+ 0\.25 \* sh \+ dr \* 0\.06, 0\.0, 0\.5\);/);
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assert.match(sksl, /float a1 = clamp\(0\.25 \+ 0\.25 \* 0\.5 \* sh \+ dr \* 0\.06, 0\.0, 0\.5\);/);
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assert.match(sksl, /float a0 = clamp\(0\.25 \* bl \+ dr \* 0\.12, 0\.0, a1\);/);
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assert.doesNotMatch(sksl, /o \+= dr \* 0\.12/, 'DR is an additive term again — it folds the flat stretch at 0.238');
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// Straight between the knots, and NOT a smoothstep: an S-curve through the
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@@ -173,7 +175,7 @@ function ramp(t, k) {
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const hlMask = clamp01(smoothstep(0.5, 0.75, t) - whMask);
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const a4 = 1 + A * wh - dr * 0.18;
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const a3 = Math.min(a4, Math.max(0.5, 0.75 + A * hl - dr * 0.09));
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const a1 = Math.min(0.5, Math.max(0, 0.25 + A * sh + dr * 0.06));
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const a1 = Math.min(0.5, Math.max(0, 0.25 + A * 0.5 * sh + dr * 0.06));
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const a0 = Math.min(a1, Math.max(0, A * bl + dr * 0.12));
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let o = mix(a0, a1, lin(0, 0.25, t));
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o = mix(o, mix(a1, 0.5, lin(0.25, 0.5, t)), step(0.25, t));
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@@ -235,12 +237,15 @@ for (const k of combos) {
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}
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assert.ok(worst > -1e-12, `worst step ${worst} — the ramp is folded`);
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// A knob moves its own quarter, and only its own: +BLACK takes the toe off the
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// floor, +SHADOW puts the 0.25 knot on the midpoint, -HIGHLIGHT pulls the 0.75
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// knot onto it, and WHITE - rolls the head under 1.0. That is the reach a
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// tonal-range slider has — a quarter of the ramp, so the middle stays a middle.
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// floor, -HIGHLIGHT pulls the 0.75 knot onto the midpoint, and WHITE - rolls the
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// head under 1.0. That is the reach a tonal-range slider has — a quarter of the
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// ramp, so the middle stays a middle. SHADOW is the exception and moves HALF of
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// it: its knot is the HEAD of the 0.25..0.50 band, so a whole quarter would draw
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// that band flat, which is the wash-out the knob was reported for.
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close(ramp(0, {}).o, 0, 'a neutral toe moved');
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close(ramp(0, { bl: 1 }).o, A, 'BLACK no longer reaches a quarter of the ramp');
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close(ramp(0.25, { sh: 1 }).o, 0.5, 'SHADOW no longer reaches the midpoint');
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close(ramp(0.25, { sh: 1 }).o, 0.375, 'SHADOW no longer stops halfway to the midpoint');
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close(ramp(0.25, { sh: -1 }).o, 0.125, 'SHADOW no longer stops halfway to the floor');
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close(ramp(0.75, { hl: -1 }).o, 0.5, 'HIGHLIGHT no longer reaches the midpoint');
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close(ramp(1, { wh: -1 }).o, 0.75, 'WHITE no longer rolls the head under 1.0');
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close(ramp(0.25, {}).o, 0.25, 'a neutral knot moved');
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@@ -259,11 +264,48 @@ close(ramp(1, { dr: 1 }).o, 0.82, 'DR no longer rolls the head the way it did');
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close(ramp(0.5, { dr: 1 }).o, 0.5, 'DR moved the midpoint');
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// Black and shadow both at -1 are the flat stretch DR used to fold: the toe is
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// held on the floor by the ordering clamp (BLACK's -0.25 cancels DR's +0.12),
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// the 0.25 knot is DR's own +0.06, and the stretch between them is a straight
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// line up to the midpoint — never a step down.
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// the 0.25 knot is DR's own +0.06 over SHADOW's half-anchor -0.125, and the
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// stretch between them is a straight line up to the midpoint — never a step
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// down.
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assert.equal(ramp(0, { dr: 1, bl: -1, sh: -1 }).o, 0);
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assert.equal(ramp(0.25, { dr: 1, bl: -1, sh: -1 }).o, 0.06);
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close(ramp(0.375, { dr: 1, bl: -1, sh: -1 }).o, 0.28, 'DR folded the flat stretch');
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assert.equal(ramp(0.25, { dr: 1, bl: -1, sh: -1 }).o, 0.185);
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close(ramp(0.375, { dr: 1, bl: -1, sh: -1 }).o, 0.3425, 'DR folded the flat stretch');
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// The band above SHADOW is the one that pays for its lift, and HALF its slope is
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// the floor the fix is. Measured on a real frame (DSCF1701, 21% of its pixels in
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// that band) with SHADOW +90, a whole anchor left 0.10 of the band's own spread
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// where half leaves 0.55 — see the note on a1 in toneShader.ts and the sweep in
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// scratchpad sh-band.mjs. Swept here over the knob's whole travel: neither
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// quarter of the ramp SHADOW touches may be drawn flatter than half its slope,
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// and neither may be stretched past one and a half, which is the same defect
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// upside down (a crush that flattens the darks into one black).
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for (let sh = -1; sh <= 1.0001; sh += 1 / 64) {
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const below = (ramp(0.25, { sh }).o - ramp(0, { sh }).o) / 0.25;
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const band = (ramp(0.5, { sh }).o - ramp(0.25, { sh }).o) / 0.25;
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assert.ok(band >= 0.5 - 1e-12, `SHADOW drew the band above it flat at ${sh}: slope ${band}`);
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assert.ok(below >= 0.5 - 1e-12, `SHADOW drew the quarter below it flat at ${sh}: slope ${below}`);
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assert.ok(band <= 1.5 + 1e-12, `SHADOW stretched the band above it at ${sh}: slope ${band}`);
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}
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// The film stocks ride the same knot, so a halved SHADOW would have halved their
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// crush with it. They are written at DOUBLE for that reason, and the look they
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// were tuned to is the knot, not the unit: these three land where they always
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// did (0.18 Classic Chrome/Vivid, 0.22 Acros, 0.17 Acros HC).
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const filmTone = tone.match(/const FILM_TONE[\s\S]*?\n};/)?.[0];
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assert.ok(filmTone, 'FILM_TONE is gone — the stocks no longer shape the ramp at all');
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// The keys are quoted or not depending on whether they are identifiers, so the
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// quotes come off before the lookup.
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const filmFlat = filmTone.replace(/['"]/g, '');
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for (const [name, sh, knot] of [
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['classic-chrome', -0.56, 0.18],
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['classic-vivid', -0.56, 0.18],
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['monochrome', -0.24, 0.22],
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['mono-high-contrast', -0.64, 0.17],
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]) {
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assert.ok(
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filmFlat.includes(`${name}: { sh: ${sh}`),
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`${name} is not on the doubled ${sh} — the stock's crush moved with the knob's reach`
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);
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close(ramp(0.25, { sh }).o, knot, `${name}'s shadow knot moved`);
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}
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// The two ends stay ordered even at full deflection against each other: the toe
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// can never climb past the head.
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for (const bl of [-1, 1])
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