Implement Decode entry in Indexed images

src/core/colorspace.js

@@ -492,7 +492,7 @@ class AlternateCS extends ColorSpace {
                                      alpha01);
   }
 
-  isDefaultDecode(decodeMap) {
+  isDefaultDecode(decodeMap, bpc) {
     return ColorSpace.isDefaultDecode(decodeMap, this.numComps);
   }
 }
@@ -565,8 +565,19 @@ class IndexedCS extends ColorSpace {
     return this.base.getOutputLength(inputLength * this.base.numComps, alpha01);
   }
 
-  isDefaultDecode(decodeMap) {
-    return true; // Indexed color maps shouldn't be changed.
+  isDefaultDecode(decodeMap, bpc) {
+    if (!Array.isArray(decodeMap)) {
+      return true;
+    }
+    if (decodeMap.length !== 2) {
+      warn('Decode map length is not correct');
+      return true;
+    }
+    if (!Number.isInteger(bpc) || bpc < 1) {
+      warn('Bits per component is not correct');
+      return true;
+    }
+    return decodeMap[0] === 0 && decodeMap[1] === (1 << bpc) - 1;
   }
 }
 
@@ -609,7 +620,7 @@ class DeviceGrayCS extends ColorSpace {
     return inputLength * (3 + alpha01);
   }
 
-  isDefaultDecode(decodeMap) {
+  isDefaultDecode(decodeMap, bpc) {
     return ColorSpace.isDefaultDecode(decodeMap, this.numComps);
   }
 }
@@ -661,7 +672,7 @@ class DeviceRgbCS extends ColorSpace {
     return bits === 8;
   }
 
-  isDefaultDecode(decodeMap) {
+  isDefaultDecode(decodeMap, bpc) {
     return ColorSpace.isDefaultDecode(decodeMap, this.numComps);
   }
 }
@@ -744,7 +755,7 @@ const DeviceCmykCS = (function DeviceCmykCSClosure() {
       return (inputLength / 4 * (3 + alpha01)) | 0;
     }
 
-    isDefaultDecode(decodeMap) {
+    isDefaultDecode(decodeMap, bpc) {
       return ColorSpace.isDefaultDecode(decodeMap, this.numComps);
     }
   }
@@ -847,7 +858,7 @@ const CalGrayCS = (function CalGrayCSClosure() {
       return inputLength * (3 + alpha01);
     }
 
-    isDefaultDecode(decodeMap) {
+    isDefaultDecode(decodeMap, bpc) {
       return ColorSpace.isDefaultDecode(decodeMap, this.numComps);
     }
   }
@@ -1129,7 +1140,7 @@ const CalRGBCS = (function CalRGBCSClosure() {
       return (inputLength * (3 + alpha01) / 3) | 0;
     }
 
-    isDefaultDecode(decodeMap) {
+    isDefaultDecode(decodeMap, bpc) {
       return ColorSpace.isDefaultDecode(decodeMap, this.numComps);
     }
   }
@@ -1280,7 +1291,7 @@ const LabCS = (function LabCSClosure() {
       return (inputLength * (3 + alpha01) / 3) | 0;
     }
 
-    isDefaultDecode(decodeMap) {
+    isDefaultDecode(decodeMap, bpc) {
       // XXX: Decoding is handled with the lab conversion because of the strange
       // ranges that are used.
       return true;

src/core/evaluator.js

@@ -100,6 +100,7 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
     }
     var cs = ColorSpace.parse(dict.get('ColorSpace', 'CS'), xref, res,
                               pdfFunctionFactory);
+    // isDefaultDecode() of DeviceGray and DeviceRGB needs no `bpc` argument.
     return (cs.name === 'DeviceGray' || cs.name === 'DeviceRGB') &&
            cs.isDefaultDecode(dict.getArray('Decode', 'D'));
   };
@@ -114,8 +115,9 @@ var PartialEvaluator = (function PartialEvaluatorClosure() {
     }
     var cs = ColorSpace.parse(dict.get('ColorSpace', 'CS'), xref, res,
                               pdfFunctionFactory);
+    const bpc = dict.get('BitsPerComponent', 'BPC') || 1;
     return (cs.numComps === 1 || cs.numComps === 3) &&
-           cs.isDefaultDecode(dict.getArray('Decode', 'D'));
+           cs.isDefaultDecode(dict.getArray('Decode', 'D'), bpc);
   };
 
   function PartialEvaluator({ pdfManager, xref, handler, pageIndex, idFactory,

src/core/image.js

@@ -169,18 +169,21 @@ var PDFImage = (function PDFImageClosure() {
     this.decode = dict.getArray('Decode', 'D');
     this.needsDecode = false;
     if (this.decode &&
-        ((this.colorSpace && !this.colorSpace.isDefaultDecode(this.decode)) ||
+        ((this.colorSpace &&
+          !this.colorSpace.isDefaultDecode(this.decode, bitsPerComponent)) ||
          (isMask && !ColorSpace.isDefaultDecode(this.decode, 1)))) {
       this.needsDecode = true;
       // Do some preprocessing to avoid more math.
       var max = (1 << bitsPerComponent) - 1;
       this.decodeCoefficients = [];
       this.decodeAddends = [];
+      const isIndexed = this.colorSpace && this.colorSpace.name === 'Indexed';
       for (var i = 0, j = 0; i < this.decode.length; i += 2, ++j) {
         var dmin = this.decode[i];
         var dmax = this.decode[i + 1];
-        this.decodeCoefficients[j] = dmax - dmin;
-        this.decodeAddends[j] = max * dmin;
+        this.decodeCoefficients[j] = isIndexed ? ((dmax - dmin) / max) :
+                                                 (dmax - dmin);
+        this.decodeAddends[j] = isIndexed ? dmin : (max * dmin);
       }
     }
 

test/pdfs/.gitignore

@@ -251,6 +251,7 @@
 !bug878026.pdf
 !issue1045.pdf
 !issue5010.pdf
+!issue10339_reduced.pdf
 !issue4934.pdf
 !issue4650.pdf
 !issue6721_reduced.pdf

test/test_manifest.json

@@ -2643,6 +2643,12 @@
       "link": false,
       "type": "eq"
     },
+    {  "id": "issue10339",
+       "file": "pdfs/issue10339_reduced.pdf",
+       "md5": "e34ef74f188080f8194c7d8e8b68c562",
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "issue1721",
       "file": "pdfs/issue1721.pdf",
       "md5": "b47177f9e5197a76ec498733ecab60e6",

test/unit/colorspace_spec.js

@@ -496,7 +496,7 @@ describe('colorspace', function () {
       expect(colorSpace.getRgb([2], 0)).toEqual(
         new Uint8ClampedArray([255, 109, 70]));
       expect(colorSpace.isPassthrough(8)).toBeFalsy();
-      expect(colorSpace.isDefaultDecode([0, 1])).toBeTruthy();
+      expect(colorSpace.isDefaultDecode([0, 1], 1)).toBeTruthy();
       expect(testDest).toEqual(expectedDest);
     });
   });