diff --git a/src/display/canvas.js b/src/display/canvas.js
index c9864ec70..40a2bc1df 100644
--- a/src/display/canvas.js
+++ b/src/display/canvas.js
@@ -191,6 +191,18 @@ function compileType3Glyph(imgData) {
   var points = new Uint8Array(width1 * (height + 1));
   var POINT_TYPES =
       new Uint8Array([0, 2, 4, 0, 1, 0, 5, 4, 8, 10, 0, 8, 0, 2, 1, 0]);
+
+  // decodes bit-packed mask data
+  var lineSize = (width + 7) & ~7, data0 = imgData.data;
+  var data = new Uint8Array(lineSize * height), pos = 0, ii;
+  for (i = 0, ii = data0.length; i < ii; i++) {
+    var mask = 128, elem = data0[i];
+    while (mask > 0) {
+      data[pos++] = (elem & mask) ? 0 : 255;
+      mask >>= 1;
+    }
+  }
+
   // finding iteresting points: every point is located between mask pixels,
   // so there will be points of the (width + 1)x(height + 1) grid. Every point
   // will have flags assigned based on neighboring mask pixels:
@@ -201,24 +213,25 @@ function compileType3Glyph(imgData) {
   //   - outside corners: 1, 2, 4, 8;
   //   - inside corners: 7, 11, 13, 14;
   //   - and, intersections: 5, 10.
-  var pos = 3, data = imgData.data, lineSize = width * 4, count = 0;
-  if (data[3] !== 0) {
+  var count = 0;
+  pos = 0;
+  if (data[pos] !== 0) {
     points[0] = 1;
     ++count;
   }
   for (j = 1; j < width; j++) {
-    if (data[pos] !== data[pos + 4]) {
+    if (data[pos] !== data[pos + 1]) {
       points[j] = data[pos] ? 2 : 1;
       ++count;
     }
-    pos += 4;
+    pos++;
   }
   if (data[pos] !== 0) {
     points[j] = 2;
     ++count;
   }
-  pos += 4;
   for (i = 1; i < height; i++) {
+    pos = i * lineSize;
     j0 = i * width1;
     if (data[pos - lineSize] !== data[pos]) {
       points[j0] = data[pos] ? 1 : 8;
@@ -228,37 +241,36 @@ function compileType3Glyph(imgData) {
     // array (in order 8-1-2-4, so we can use '>>2' to shift the column).
     var sum = (data[pos] ? 4 : 0) + (data[pos - lineSize] ? 8 : 0);
     for (j = 1; j < width; j++) {
-      sum = (sum >> 2) + (data[pos + 4] ? 4 : 0) +
-            (data[pos - lineSize + 4] ? 8 : 0);
+      sum = (sum >> 2) + (data[pos + 1] ? 4 : 0) +
+            (data[pos - lineSize + 1] ? 8 : 0);
       if (POINT_TYPES[sum]) {
         points[j0 + j] = POINT_TYPES[sum];
         ++count;
       }
-      pos += 4;
+      pos++;
     }
     if (data[pos - lineSize] !== data[pos]) {
       points[j0 + j] = data[pos] ? 2 : 4;
       ++count;
     }
-    pos += 4;
 
     if (count > POINT_TO_PROCESS_LIMIT) {
       return null;
     }
   }
 
-  pos -= lineSize;
+  pos = lineSize * (height - 1);
   j0 = i * width1;
   if (data[pos] !== 0) {
     points[j0] = 8;
     ++count;
   }
   for (j = 1; j < width; j++) {
-    if (data[pos] !== data[pos + 4]) {
+    if (data[pos] !== data[pos + 1]) {
       points[j0 + j] = data[pos] ? 4 : 8;
       ++count;
     }
-    pos += 4;
+    pos++;
   }
   if (data[pos] !== 0) {
     points[j0 + j] = 4;