// PROBE 1886 — v1.1 — two-point stop meter, standardized on ITU-R BT.1886 // Federico Malpica, 2026-07-04 // // A stop-difference tape measure. Place point A (green) and point B (red) with // the position sliders; the readout box shows, per row: // row 1 (green square) A stops + A signal level (pale blue, percent) // row 2 (red square) B stops + B signal level (pale blue, percent) // row 3 (white square) D = A minus B stops (positive = A is brighter) // White numbers = stops (light, through BT.1886). Pale blue = display signal // percent (what the waveform shows, 0-100). Same patch, two rulers. // v1.1: Readout Scale slider + border (visibility on letterboxed frames) + // signal pct columns. // v1.2: Readout X/Y Pct sliders replace Readout Side — output blanking is // applied AFTER the node and covers anything under the bars, so the box is // freely positionable; defaults clear a 2.39 bar on 16:9. // Put A on the key side of the face, B on the fill side: D = your lighting // ratio in stops (1.0 = 2:1 · 1.6 = 3:1 · 2.0 = 4:1). A on key, B on the // background: D = subject/background separation. Match the reference's D on // your own shot through your own look = the final images match. // // Each point averages a square patch (side = 2 x Sample Radius) in LINEAR // light — 9x9 grid taps, so small Sample Radius = tight probe, large = area // mean. Marks: crosshair + patch outline at each point. // // TEXTURE-BASED (samples away from the current pixel): // - apply as a DCTL via the OFX panel, NOT the LUT browser (May finding) // - all toggles are 0-1 sliders — CHECK_BOX breaks compilation next to // __TEXTURE__ params (May finding) // // Mid Gray Anchor must match your EXPOSURE 1886 setting (default 0.409) so the // A and B absolute numbers agree with what EXPOSURE 1886 paints. The D row // does not depend on it. Readout X/Y Pct place the box (0,0 = top left, // 100,100 = bottom right — always fully on frame). DEFINE_UI_PARAMS(ax, Point A X Pct, DCTLUI_SLIDER_FLOAT, 30.0, 0.0, 100.0, 0.1) DEFINE_UI_PARAMS(ay, Point A Y Pct, DCTLUI_SLIDER_FLOAT, 40.0, 0.0, 100.0, 0.1) DEFINE_UI_PARAMS(bx, Point B X Pct, DCTLUI_SLIDER_FLOAT, 70.0, 0.0, 100.0, 0.1) DEFINE_UI_PARAMS(by, Point B Y Pct, DCTLUI_SLIDER_FLOAT, 40.0, 0.0, 100.0, 0.1) DEFINE_UI_PARAMS(sampleRadius, Sample Radius Px, DCTLUI_SLIDER_INT, 15, 3, 80, 1) DEFINE_UI_PARAMS(midAnchor, Mid Gray Anchor, DCTLUI_SLIDER_FLOAT, 0.409, 0.05, 0.95, 0.001) DEFINE_UI_PARAMS(showMarks, Show Marks, DCTLUI_SLIDER_INT, 1, 0, 1, 1) DEFINE_UI_PARAMS(readoutX, Readout X Pct, DCTLUI_SLIDER_FLOAT, 1.0, 0.0, 100.0, 0.1) DEFINE_UI_PARAMS(readoutY, Readout Y Pct, DCTLUI_SLIDER_FLOAT, 16.0, 0.0, 100.0, 0.1) DEFINE_UI_PARAMS(readoutScale, Readout Scale, DCTLUI_SLIDER_INT, 2, 1, 6, 1) __DEVICE__ float g24_inv(float v) { return _powf(_fmaxf(v, 0.0f), 2.4f); // BT.1886 EOTF (zero black lift form) } __DEVICE__ int glyph_bits(int d) { if (d == 0) return 0x7B6F; if (d == 1) return 0x2C97; if (d == 2) return 0x73E7; if (d == 3) return 0x73CF; if (d == 4) return 0x5BC9; if (d == 5) return 0x79CF; if (d == 6) return 0x79EF; if (d == 7) return 0x7249; if (d == 8) return 0x7BEF; if (d == 9) return 0x7BCF; if (d == 11) return 0x0002; // decimal point (bottom center) return 0x01C0; // minus } __DEVICE__ float3 transform(int p_Width, int p_Height, int p_X, int p_Y, __TEXTURE__ p_TexR, __TEXTURE__ p_TexG, __TEXTURE__ p_TexB) { float3 src = make_float3(_tex2D(p_TexR, p_X, p_Y), _tex2D(p_TexG, p_X, p_Y), _tex2D(p_TexB, p_X, p_Y)); float axp = ax * 0.01f * (float)(p_Width - 1); float ayp = ay * 0.01f * (float)(p_Height - 1); float bxp = bx * 0.01f * (float)(p_Width - 1); float byp = by * 0.01f * (float)(p_Height - 1); float rad = (float)sampleRadius; // ---- MARKS: crosshair + patch outline at A (green) and B (red) ---- if (showMarks == 1) { float th = _fmaxf(1.0f, (float)p_Height / 720.0f); float arm = rad + 8.0f * th; float dxa = _fabs((float)p_X - axp); float dya = _fabs((float)p_Y - ayp); float dxb = _fabs((float)p_X - bxp); float dyb = _fabs((float)p_Y - byp); int onA = ((dxa <= th && dya <= arm) || (dya <= th && dxa <= arm) || (_fmaxf(dxa, dya) >= rad - th && _fmaxf(dxa, dya) <= rad + th)) ? 1 : 0; int onB = ((dxb <= th && dyb <= arm) || (dyb <= th && dxb <= arm) || (_fmaxf(dxb, dyb) >= rad - th && _fmaxf(dxb, dyb) <= rad + th)) ? 1 : 0; if (onA == 1) return make_float3(0.15f, 0.95f, 0.30f); if (onB == 1) return make_float3(1.00f, 0.20f, 0.12f); } // ---- READOUT BOX (only these pixels pay for the sampling) ---- int sc = readoutScale * (int)_fmaxf(2.0f, _floorf((float)p_Height / 460.0f)); int pad = 3 * sc; int rh = 7 * sc; // row height: 5*sc glyph + gap int bw = 36 * sc + 2 * pad; // label + stops digits + signal pct digits int bh = 3 * rh + 2 * pad; // position as pct of the available travel: any value keeps the box on-frame; // default Y 14 clears a 2.39 blanking bar on a 16:9 timeline (blanking is // applied AFTER the node, so it covers anything drawn under the bars) int bx0 = (int)(readoutX * 0.01f * (float)(p_Width - bw)); int by0 = (int)(readoutY * 0.01f * (float)(p_Height - bh)); if (p_X >= bx0 && p_X < bx0 + bw && p_Y >= by0 && p_Y < by0 + bh) { // 9x9 grid taps over each square patch, averaged in LINEAR light // (inlined — texture handles stay inside transform for the Metal compiler) float accA = 0.0f; float accB = 0.0f; float accAd = 0.0f; // display-domain luma (waveform level) float accBd = 0.0f; for (int j = -4; j <= 4; j++) { for (int i = -4; i <= 4; i++) { float ox = (float)i * rad * 0.25f; float oy = (float)j * rad * 0.25f; float sxa = _fminf(_fmaxf(axp + ox, 0.0f), (float)(p_Width - 1)); float sya = _fminf(_fmaxf(ayp + oy, 0.0f), (float)(p_Height - 1)); float sxb = _fminf(_fmaxf(bxp + ox, 0.0f), (float)(p_Width - 1)); float syb = _fminf(_fmaxf(byp + oy, 0.0f), (float)(p_Height - 1)); float ra = _tex2D(p_TexR, (int)sxa, (int)sya); float ga = _tex2D(p_TexG, (int)sxa, (int)sya); float ba = _tex2D(p_TexB, (int)sxa, (int)sya); float rb = _tex2D(p_TexR, (int)sxb, (int)syb); float gb = _tex2D(p_TexG, (int)sxb, (int)syb); float bb = _tex2D(p_TexB, (int)sxb, (int)syb); accA += 0.2126f * g24_inv(ra) + 0.7152f * g24_inv(ga) + 0.0722f * g24_inv(ba); accB += 0.2126f * g24_inv(rb) + 0.7152f * g24_inv(gb) + 0.0722f * g24_inv(bb); accAd += 0.2126f * ra + 0.7152f * ga + 0.0722f * ba; accBd += 0.2126f * rb + 0.7152f * gb + 0.0722f * bb; } } float yref = _fmaxf(g24_inv(midAnchor), 1e-6f); float la = _fmaxf(accA / 81.0f, 1e-6f); float lb = _fmaxf(accB / 81.0f, 1e-6f); float stopsA = _log2f(la / yref); float stopsB = _log2f(lb / yref); float sigA = accAd / 81.0f * 100.0f; // display signal level, percent float sigB = accBd / 81.0f * 100.0f; float3 col = make_float3(0.07f, 0.07f, 0.07f); // border so the panel reads against black letterbox bars if (p_X - bx0 < 2 || (bx0 + bw - 1 - p_X) < 2 || p_Y - by0 < 2 || (by0 + bh - 1 - p_Y) < 2) return make_float3(0.45f, 0.45f, 0.45f); int row = (p_Y - by0 - pad) / rh; int ry = (p_Y - by0 - pad) - row * rh; if (row >= 0 && row <= 2 && ry >= 0 && ry < 5 * sc) { float val = (row == 0) ? stopsA : ((row == 1) ? stopsB : (stopsA - stopsB)); val = _fminf(_fmaxf(val, -9.9f), 9.9f); int dx = p_X - (bx0 + pad); int gy = ry / sc; int gxt = dx / sc; // label square in slot 0 (rows of 3x5 like a glyph, all on) if (gxt >= 0 && gxt <= 2) { if (row == 0) col = make_float3(0.15f, 0.95f, 0.30f); else if (row == 1) col = make_float3(1.00f, 0.20f, 0.12f); else col = make_float3(0.90f, 0.90f, 0.90f); } else if (gxt >= 4 && gxt <= 19) // stops columns { int neg = (val < -0.05f) ? 1 : 0; int r10 = (int)_floorf(_fabs(val) * 10.0f + 0.5f); int du = r10 / 10; int dt = r10 - du * 10; int nd = neg + 3; // [minus] unit point tenth int gi = (gxt - 4) / 4; int ggx = (gxt - 4) - gi * 4; if (gi < nd && ggx <= 2 && gy >= 0 && gy <= 4) { int slot = gi - neg; int d = 10; if (slot == 0) d = du; else if (slot == 1) d = 11; else if (slot == 2) d = dt; if (slot >= 0 || gi == 0) { int bits = glyph_bits(d); if (((bits >> (14 - (gy * 3 + ggx))) & 1) == 1) col = make_float3(1.0f, 1.0f, 1.0f); } } } else if (gxt >= 22 && row <= 1) // signal pct columns, A and B rows only { float sig = (row == 0) ? sigA : sigB; int pv = (int)_floorf(_fminf(_fmaxf(sig, 0.0f), 100.0f) + 0.5f); int dh = pv / 100; int dt2 = (pv / 10) - dh * 10; int du2 = pv - (pv / 10) * 10; int nd = (pv >= 100) ? 3 : ((pv >= 10) ? 2 : 1); int gi = (gxt - 22) / 4; int ggx = (gxt - 22) - gi * 4; if (gi < nd && ggx <= 2 && gy >= 0 && gy <= 4) { int d = du2; if (nd == 3) d = (gi == 0) ? dh : ((gi == 1) ? dt2 : du2); else if (nd == 2) d = (gi == 0) ? dt2 : du2; int bits = glyph_bits(d); if (((bits >> (14 - (gy * 3 + ggx))) & 1) == 1) col = make_float3(0.55f, 0.75f, 1.00f); // pale blue = signal pct } } } return col; } return src; }