Lab color space, closes #1133

src/colorspace.js

@@ -416,28 +416,103 @@ var DeviceCmykCS = (function DeviceCmykCSClosure() {
   return DeviceCmykCS;
 })();
 
+//
+// LabCS: Based on "PDF Reference, Sixth Ed", p.250
+//
 var LabCS = (function LabCSClosure() {
   function LabCS(whitePoint, blackPoint, range) {
     this.name = 'Lab';
     this.numComps = 3;
     this.defaultColor = [0, 0, 0];
-    this.whitePoint = whitePoint;
-    this.blackPoint = blackPoint;
-    this.range = range;
+
+    if (!whitePoint)
+      error('WhitePoint missing - required for color space Lab');
+    blackPoint = blackPoint || [0, 0, 0];
+    range = range || [-100, 100, -100, 100];
+
+    // Translate args to spec variables
+    this.XW = whitePoint[0];
+    this.YW = whitePoint[1];
+    this.ZW = whitePoint[2];
+    this.amin = range[0];
+    this.amax = range[1];
+    this.bmin = range[2];
+    this.bmax = range[3];
+
+    // These are here just for completeness - the spec doesn't offer any
+    // formulas that use BlackPoint in Lab
+    this.XB = blackPoint[0];
+    this.YB = blackPoint[1];
+    this.ZB = blackPoint[2];
+
+    // Validate vars as per spec
+    if (this.XW < 0 || this.ZW < 0 || this.YW !== 1)
+      error('Invalid WhitePoint components, no fallback available');
+
+    if (this.XB < 0 || this.YB < 0 || this.ZB < 0) {
+      warn('Invalid BlackPoint, falling back to default');
+      this.XB = this.YB = this.ZB = 0;
+    }
+
+    if (this.amin > this.amax || this.bmin > this.bmax) {
+      warn('Invalid Range, falling back to defaults');
+      this.amin = -100;
+      this.amax = 100;
+      this.bmin = -100;
+      this.bmax = 100;
+    }
+  };
+
+  // Function g(x) from spec
+  function g(x) {
+    if (x >= 6 / 29)
+      return x * x * x;
+    else
+      return (108 / 841) * (x - 4 / 29);
   }
+
   LabCS.prototype = {
     getRgb: function labcs_getRgb(color) {
-      return [0, 0, 0];
+      // Ls,as,bs <---> L*,a*,b* in the spec
+      var Ls = color[0], as = color[1], bs = color[2];
+
+      // Adjust limits of 'as' and 'bs'
+      as = as > this.amax ? this.amax : as;
+      as = as < this.amin ? this.amin : as;
+      bs = bs > this.bmax ? this.bmax : bs;
+      bs = bs < this.bmin ? this.bmin : bs;
+
+      // Computes intermediate variables X,Y,Z as per spec
+      var M = (Ls + 16) / 116;
+      var L = M + (as / 500);
+      var N = M - (bs / 200);
+      var X = this.XW * g(L);
+      var Y = this.YW * g(M);
+      var Z = this.ZW * g(N);
+
+      // XYZ to RGB 3x3 matrix, from:
+      // http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC18
+      var XYZtoRGB = [3.240479, -1.537150, -0.498535,
+                      -0.969256, 1.875992, 0.041556,
+                      0.055648, -0.204043, 1.057311];
+
+      return Util.apply3dTransform(XYZtoRGB, [X, Y, Z]);
     },
     getRgbBuffer: function labcs_getRgbBuffer(input, bits) {
       if (bits == 8)
         return input;
       var scale = 255 / ((1 << bits) - 1);
-      var i, length = input.length;
+      var i, length = input.length / 3;
       var rgbBuf = new Uint8Array(length);
 
-      for (i = 0; i < length; ++i)
-        rgbBuf[i] = 0;
+      var j = 0;
+      for (i = 0; i < length; ++i) {
+        // Convert L*, a*, s* into RGB
+        var rgb = this.getRgb([input[i], input[i + 1], input[i + 2]]);
+        rgbBuf[j++] = rgb[0];
+        rgbBuf[j++] = rgb[1];
+        rgbBuf[j++] = rgb[2];
+      }
 
       return rgbBuf;
     },

src/util.js

@@ -78,21 +78,39 @@ var IDENTITY_MATRIX = [1, 0, 0, 1, 0, 0];
 
 var Util = (function UtilClosure() {
   function Util() {}
+
   Util.makeCssRgb = function makergb(r, g, b) {
     var ri = (255 * r) | 0, gi = (255 * g) | 0, bi = (255 * b) | 0;
     return 'rgb(' + ri + ',' + gi + ',' + bi + ')';
   };
+
   Util.makeCssCmyk = function makecmyk(c, m, y, k) {
     c = (new DeviceCmykCS()).getRgb([c, m, y, k]);
     var ri = (255 * c[0]) | 0, gi = (255 * c[1]) | 0, bi = (255 * c[2]) | 0;
     return 'rgb(' + ri + ',' + gi + ',' + bi + ')';
   };
+
+  // For 2d affine transforms
   Util.applyTransform = function apply(p, m) {
     var xt = p[0] * m[0] + p[1] * m[2] + m[4];
     var yt = p[0] * m[1] + p[1] * m[3] + m[5];
     return [xt, yt];
   };
 
+  // Apply a generic 3d matrix M on a 3-vector v:
+  //   | a b c |   | X |
+  //   | d e f | x | Y |
+  //   | g h i |   | Z |
+  // M is assumed to be serialized as [a,b,c,d,e,f,g,h,i],
+  // with v as [X,Y,Z]
+  Util.apply3dTransform = function apply3d(m, v) {
+    return [
+      m[0] * v[0] + m[1] * v[1] + m[2] * v[2],
+      m[3] * v[0] + m[4] * v[1] + m[5] * v[2],
+      m[6] * v[0] + m[7] * v[1] + m[8] * v[2]
+    ];
+  }
+
   return Util;
 })();
 

test/pdfs/issue1133.pdf.link

@@ -0,0 +1 @@
+http://www.cscw2012.org/docs/program.pdf

test/test_manifest.json

@@ -444,5 +444,12 @@
       "rounds": 1,
       "link": false,
       "type": "eq"
+    },
+    {  "id": "issue1133",
+      "file": "pdfs/issue1133.pdf",
+      "md5": "d1b61580cb100e3df93d33703af1773a",
+      "rounds": 1,
+      "link": true,
+      "type": "eq"
     }
 ]