[css-color-hdr] Add missing Jzazbz_to_XYZ, #9934

Author: svgeesus

css-color-hdr-1/jzazbz.js

@@ -59,3 +59,58 @@ function LMStoJzazbz(LMS) {
     return [Jz, az, bz];
 }
 
+function Jzazbz_to_XYZ (Jzazbz) {
+    // convert an array of JzAzBz to D65 XYZ
+    // such that [0,0,0] is black and
+    // media white is [0.2220, -0.00016, -0.0001]
+
+    const b = 1.15;
+    const g = 0.66;
+    const M = [
+        [  1.9242264357876067,  -1.0047923125953657,  0.037651404030618   ],
+        [  0.35031676209499907,  0.7264811939316552, -0.06538442294808501 ],
+        [ -0.09098281098284752, -0.3127282905230739,  1.5227665613052603  ],
+    ];
+
+    let LMS = Jzazbz_to_LMS (Jzazbz);
+    // modified absolute XYZ
+	let [Xm, Ym, Za] = multiplyMatrices(LMS, M);
+
+    // un-modify X and Y to get D65 XYZ, relative to media white
+    let Xa = (Xm + (b - 1) * Za) / b;
+    let Ya = (Ym + (g - 1) * Xa) / g;
+    return [Xa, Ya, Za];
+}
+
+function Jzazbz_to_LMS (Jzazbz) {
+
+    const d = -0.56;
+    const d0 = 1.6295499532821566e-11;
+    const c1 = 3424 / 2 ** 12;
+    const c2 = 2413 / 2 ** 7;
+    const c3 = 2392 / 2 ** 7;
+    const pinv = 2 ** 5 / (1.7 * 2523);
+    const M = [
+        [ 1,  0.13860504327153927,   0.05804731615611883  ],
+        [ 1, -0.1386050432715393,   -0.058047316156118904 ],
+        [ 1, -0.09601924202631895,  -0.81189189605603900  ],
+    ];
+
+    let [Jz, az, bz] = Jzazbz;
+	let Iz = (Jz + d0) / (1 + d - d * (Jz + d0));
+
+    // bring into LMS cone domain
+	let PQLMS = multiplyMatrices([Iz, az, bz], M);
+
+    // convert from PQ-coded to linear-light LMS
+    let LMS = (
+        PQLMS.map(function (val) {
+            let num = c1 - spow(val, pinv);
+            let denom = c3 * spow(val, pinv) - c2;
+            let x = 10000 * spow(num / denom, ninv);
+
+            return x; // luminance relative to diffuse white, [0, 70 or so].
+        })
+    );
+    return LMS;
+}