Enable/disable image smoothing based on image interpolate value. (bug…

… 1722191)

While some of the output looks worse to my eye, this behavior more
closely matches what I see when I open the PDFs in Adobe acrobat.

Fixes: #4706, #9713

src/core/evaluator.js

@@ -589,6 +589,7 @@ class PartialEvaluator {
     }
 
     const imageMask = dict.get("ImageMask", "IM") || false;
+    const interpolate = dict.get("Interpolate", "I");
     let imgData, args;
     if (imageMask) {
       // This depends on a tmpCanvas being filled with the
@@ -612,6 +613,7 @@ class PartialEvaluator {
         height,
         imageIsFromDecodeStream: image instanceof DecodeStream,
         inverseDecode: !!decode && decode[0] > 0,
+        interpolate,
       });
       imgData.cached = !!cacheKey;
       args = [imgData];

src/core/image.js

@@ -139,7 +139,7 @@ class PDFImage {
     this.width = width;
     this.height = height;
 
-    this.interpolate = dict.get("Interpolate", "I") || false;
+    this.interpolate = dict.get("Interpolate", "I");
     this.imageMask = dict.get("ImageMask", "IM") || false;
     this.matte = dict.get("Matte") || false;
 
@@ -294,6 +294,7 @@ class PDFImage {
     height,
     imageIsFromDecodeStream,
     inverseDecode,
+    interpolate,
   }) {
     if (
       typeof PDFJSDev === "undefined" ||
@@ -339,7 +340,7 @@ class PDFImage {
       }
     }
 
-    return { data, width, height };
+    return { data, width, height, interpolate };
   }
 
   get drawWidth() {
@@ -593,6 +594,7 @@ class PDFImage {
     const imgData = {
       width: drawWidth,
       height: drawHeight,
+      interpolate: this.interpolate,
       kind: 0,
       data: null,
       // Other fields are filled in below.

src/display/canvas.js

@@ -37,6 +37,9 @@ const MIN_FONT_SIZE = 16;
 const MAX_FONT_SIZE = 100;
 const MAX_GROUP_SIZE = 4096;
 
+const CSS_PIXELS_PER_INCH = 96.0;
+const PDF_PIXELS_PER_INCH = 72.0;
+
 // This value comes from sampling a few PDFs that re-use patterns, there doesn't
 // seem to be any that benefit from caching more than 2 patterns.
 const MAX_CACHED_CANVAS_PATTERNS = 2;
@@ -871,6 +874,21 @@ function composeSMask(ctx, smask, layerCtx) {
   ctx.drawImage(mask, 0, 0);
 }
 
+function getImageSmoothingEnabled(transform, interpolate) {
+  const scale = Util.singularValueDecompose2dScale(transform);
+  const actualScale =
+    (window.devicePixelRatio * CSS_PIXELS_PER_INCH) / PDF_PIXELS_PER_INCH;
+  if (interpolate !== undefined) {
+    // If the value is explicitly set use it.
+    return interpolate;
+  } else if (scale[0] <= actualScale || scale[1] <= actualScale) {
+    // Smooth when downscaling.
+    return true;
+  }
+  // Don't smooth when upscaling.
+  return false;
+}
+
 const LINE_CAP_STYLES = ["butt", "round", "square"];
 const LINE_JOIN_STYLES = ["miter", "round", "bevel"];
 const NORMAL_CLIP = {};
@@ -1183,6 +1201,10 @@ class CanvasGraphics {
       maskCanvas.canvas,
       fillCtx.mozCurrentTransformInverse
     );
+    fillCtx.imageSmoothingEnabled = getImageSmoothingEnabled(
+      fillCtx.mozCurrentTransform,
+      img.interpolate
+    );
     fillCtx.drawImage(
       scaled.img,
       0,
@@ -2663,6 +2685,10 @@ class CanvasGraphics {
     }
 
     const scaled = this._scaleImage(imgToPaint, ctx.mozCurrentTransformInverse);
+    ctx.imageSmoothingEnabled = getImageSmoothingEnabled(
+      ctx.mozCurrentTransform,
+      imgData.interpolate
+    );
     ctx.drawImage(
       scaled.img,
       0,

test/pdfs/.gitignore

@@ -69,6 +69,7 @@
 !issue8229.pdf
 !issue8276_reduced.pdf
 !issue8372.pdf
+!issue9713.pdf
 !xfa_filled_imm1344e.pdf
 !issue8424.pdf
 !issue8480.pdf
@@ -150,6 +151,7 @@
 !complex_ttf_font.pdf
 !issue3694_reduced.pdf
 !extgstate.pdf
+!issue4706.pdf
 !rotation.pdf
 !simpletype3font.pdf
 !sizes.pdf

test/test_manifest.json

@@ -3110,6 +3110,12 @@
        "rounds": 1,
        "type": "eq"
     },
+    {  "id": "issue4706",
+       "file": "pdfs/issue4706.pdf",
+       "md5": "f3e90a3cf52550583fa2a07a138b8660",
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "issue11242",
        "file": "pdfs/issue11242_reduced.pdf",
        "md5": "ba50b6ee537f3e815ccfe0c99e598e05",
@@ -4421,6 +4427,12 @@
       "link": true,
       "type": "eq"
     },
+    {  "id": "issue9713",
+       "file": "pdfs/issue9713.pdf",
+       "md5": "a62bd42d12271105b26a68c8eae5ea5f",
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "issue1936-text",
        "file": "pdfs/issue1936.pdf",
        "md5": "7302eb9b6a626308e2a933aaed9e1756",