Add (basic) support for transfer functions to Images (issue 6931, bug 1149713)

This is *similar* to the existing transfer function support for SMasks, but extended to simple image data.
Please note that the extra amount of data now being sent to the worker-thread, for affected /ExtGState entries, is limited to *at most* 4 `Uint8Array`s each with a length of 256 elements.

Refer to https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/PDF32000_2008.pdf#G9.1658137 for additional details.

src/core/evaluator.js

@@ -668,6 +668,51 @@ class PartialEvaluator {
     );
   }
 
+  handleTransferFunction(tr) {
+    let transferArray;
+    if (Array.isArray(tr)) {
+      transferArray = tr;
+    } else if (isPDFFunction(tr)) {
+      transferArray = [tr];
+    } else {
+      return null; // Not a valid transfer function entry.
+    }
+
+    const transferMaps = [];
+    let numFns = 0,
+      numEffectfulFns = 0;
+    for (const entry of transferArray) {
+      const transferObj = this.xref.fetchIfRef(entry);
+      numFns++;
+
+      if (isName(transferObj, "Identity")) {
+        transferMaps.push(null);
+        continue;
+      } else if (!isPDFFunction(transferObj)) {
+        return null; // Not a valid transfer function object.
+      }
+
+      const transferFn = this._pdfFunctionFactory.create(transferObj);
+      const transferMap = new Uint8Array(256),
+        tmp = new Float32Array(1);
+      for (let j = 0; j < 256; j++) {
+        tmp[0] = j / 255;
+        transferFn(tmp, 0, tmp, 0);
+        transferMap[j] = (tmp[0] * 255) | 0;
+      }
+      transferMaps.push(transferMap);
+      numEffectfulFns++;
+    }
+
+    if (!(numFns === 1 || numFns === 4)) {
+      return null; // Only 1 or 4 functions are supported, by the specification.
+    }
+    if (numEffectfulFns === 0) {
+      return null; // Only /Identity transfer functions found, which are no-ops.
+    }
+    return transferMaps;
+  }
+
   handleTilingType(
     fn,
     args,
@@ -887,7 +932,10 @@ class PartialEvaluator {
           } else {
             warn("Unsupported SMask type");
           }
-
+          break;
+        case "TR":
+          const transferMaps = this.handleTransferFunction(value);
+          gStateObj.push([key, transferMaps]);
           break;
         // Only generate info log messages for the following since
         // they are unlikely to have a big impact on the rendering.
@@ -898,7 +946,6 @@ class PartialEvaluator {
         case "BG2":
         case "UCR":
         case "UCR2":
-        case "TR":
         case "TR2":
         case "HT":
         case "SM":

src/display/canvas.js

@@ -416,6 +416,7 @@ var CanvasExtraState = (function CanvasExtraStateClosure() {
     this.lineWidth = 1;
     this.activeSMask = null;
     this.resumeSMaskCtx = null; // nonclonable field (see the save method below)
+    this.transferMaps = null;
   }
 
   CanvasExtraState.prototype = {
@@ -484,7 +485,7 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
     this._cachedGetSinglePixelWidth = null;
   }
 
-  function putBinaryImageData(ctx, imgData) {
+  function putBinaryImageData(ctx, imgData, transferMaps = null) {
     if (typeof ImageData !== "undefined" && imgData instanceof ImageData) {
       ctx.putImageData(imgData, 0, 0);
       return;
@@ -514,6 +515,24 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
     var dest = chunkImgData.data;
     var i, j, thisChunkHeight, elemsInThisChunk;
 
+    let transferMapRed, transferMapGreen, transferMapBlue, transferMapGray;
+    if (transferMaps) {
+      switch (transferMaps.length) {
+        case 1:
+          transferMapRed = transferMaps[0];
+          transferMapGreen = transferMaps[0];
+          transferMapBlue = transferMaps[0];
+          transferMapGray = transferMaps[0];
+          break;
+        case 4:
+          transferMapRed = transferMaps[0];
+          transferMapGreen = transferMaps[1];
+          transferMapBlue = transferMaps[2];
+          transferMapGray = transferMaps[3];
+          break;
+      }
+    }
+
     // There are multiple forms in which the pixel data can be passed, and
     // imgData.kind tells us which one this is.
     if (imgData.kind === ImageKind.GRAYSCALE_1BPP) {
@@ -524,13 +543,20 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
       var fullSrcDiff = (width + 7) >> 3;
       var white = 0xffffffff;
       var black = IsLittleEndianCached.value ? 0xff000000 : 0x000000ff;
+
+      if (transferMapGray) {
+        if (transferMapGray[0] === 0xff && transferMapGray[0xff] === 0) {
+          [white, black] = [black, white];
+        }
+      }
+
       for (i = 0; i < totalChunks; i++) {
         thisChunkHeight =
           i < fullChunks ? FULL_CHUNK_HEIGHT : partialChunkHeight;
         destPos = 0;
         for (j = 0; j < thisChunkHeight; j++) {
           var srcDiff = srcLength - srcPos;
-          var k = 0;
+          let k = 0;
           var kEnd = srcDiff > fullSrcDiff ? width : srcDiff * 8 - 7;
           var kEndUnrolled = kEnd & ~7;
           var mask = 0;
@@ -565,6 +591,11 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
       }
     } else if (imgData.kind === ImageKind.RGBA_32BPP) {
       // RGBA, 32-bits per pixel.
+      const hasTransferMaps = !!(
+        transferMapRed ||
+        transferMapGreen ||
+        transferMapBlue
+      );
 
       j = 0;
       elemsInThisChunk = width * FULL_CHUNK_HEIGHT * 4;
@@ -572,16 +603,51 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
         dest.set(src.subarray(srcPos, srcPos + elemsInThisChunk));
         srcPos += elemsInThisChunk;
 
+        if (hasTransferMaps) {
+          for (let k = 0; k < elemsInThisChunk; k += 4) {
+            if (transferMapRed) {
+              dest[k + 0] = transferMapRed[dest[k + 0]];
+            }
+            if (transferMapGreen) {
+              dest[k + 1] = transferMapGreen[dest[k + 1]];
+            }
+            if (transferMapBlue) {
+              dest[k + 2] = transferMapBlue[dest[k + 2]];
+            }
+          }
+        }
+
         ctx.putImageData(chunkImgData, 0, j);
         j += FULL_CHUNK_HEIGHT;
       }
       if (i < totalChunks) {
         elemsInThisChunk = width * partialChunkHeight * 4;
         dest.set(src.subarray(srcPos, srcPos + elemsInThisChunk));
+
+        if (hasTransferMaps) {
+          for (let k = 0; k < elemsInThisChunk; k += 4) {
+            if (transferMapRed) {
+              dest[k + 0] = transferMapRed[dest[k + 0]];
+            }
+            if (transferMapGreen) {
+              dest[k + 1] = transferMapGreen[dest[k + 1]];
+            }
+            if (transferMapBlue) {
+              dest[k + 2] = transferMapBlue[dest[k + 2]];
+            }
+          }
+        }
+
         ctx.putImageData(chunkImgData, 0, j);
       }
     } else if (imgData.kind === ImageKind.RGB_24BPP) {
       // RGB, 24-bits per pixel.
+      const hasTransferMaps = !!(
+        transferMapRed ||
+        transferMapGreen ||
+        transferMapBlue
+      );
+
       thisChunkHeight = FULL_CHUNK_HEIGHT;
       elemsInThisChunk = width * thisChunkHeight;
       for (i = 0; i < totalChunks; i++) {
@@ -597,6 +663,21 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
           dest[destPos++] = src[srcPos++];
           dest[destPos++] = 255;
         }
+
+        if (hasTransferMaps) {
+          for (let k = 0; k < destPos; k += 4) {
+            if (transferMapRed) {
+              dest[k + 0] = transferMapRed[dest[k + 0]];
+            }
+            if (transferMapGreen) {
+              dest[k + 1] = transferMapGreen[dest[k + 1]];
+            }
+            if (transferMapBlue) {
+              dest[k + 2] = transferMapBlue[dest[k + 2]];
+            }
+          }
+        }
+
         ctx.putImageData(chunkImgData, 0, i * FULL_CHUNK_HEIGHT);
       }
     } else {
@@ -1040,6 +1121,8 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
             }
             this.tempSMask = null;
             break;
+          case "TR":
+            this.current.transferMaps = value;
         }
       }
     },
@@ -2362,7 +2445,7 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
       } else {
         tmpCanvas = this.cachedCanvases.getCanvas("inlineImage", width, height);
         var tmpCtx = tmpCanvas.context;
-        putBinaryImageData(tmpCtx, imgData);
+        putBinaryImageData(tmpCtx, imgData, this.current.transferMaps);
         imgToPaint = tmpCanvas.canvas;
       }
 
@@ -2447,7 +2530,7 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
 
       var tmpCanvas = this.cachedCanvases.getCanvas("inlineImage", w, h);
       var tmpCtx = tmpCanvas.context;
-      putBinaryImageData(tmpCtx, imgData);
+      putBinaryImageData(tmpCtx, imgData, this.current.transferMaps);
 
       for (var i = 0, ii = map.length; i < ii; i++) {
         var entry = map[i];

test/pdfs/.gitignore

@@ -45,6 +45,7 @@
 !issue7492.pdf
 !issue7544.pdf
 !issue7507.pdf
+!issue6931_reduced.pdf
 !issue7580.pdf
 !issue7598.pdf
 !issue7665.pdf

test/test_manifest.json

@@ -4468,6 +4468,12 @@
        "rounds": 1,
        "type": "eq"
     },
+    {  "id": "issue6931",
+       "file": "pdfs/issue6931_reduced.pdf",
+       "md5": "e61388913821a5e044bf85a5846d6d9a",
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "annotation-button-widget-annotations",
        "file": "pdfs/annotation-button-widget.pdf",
        "md5": "5cf23adfff84256d9cfe261bea96dade",