diff --git a/testing/tools/pngdiffer.py b/testing/tools/pngdiffer.py
index a1533b8..95acb19 100755
--- a/testing/tools/pngdiffer.py
+++ b/testing/tools/pngdiffer.py
@@ -4,32 +4,26 @@
 # found in the LICENSE file.
 
 import os
+import shutil
 import sys
 
 import common
 
 class PNGDiffer():
-  ACTUAL_TEMPLATE = '.pdf.%d.png'
-  EXPECTED_TEMPLATE = '_expected' + ACTUAL_TEMPLATE
-  PLATFORM_EXPECTED_TEMPLATE = '_expected_%s' + ACTUAL_TEMPLATE
-
   def __init__(self, finder):
     self.pdfium_diff_path = finder.ExecutablePath('pdfium_diff')
     self.os_name = finder.os_name
 
   def GetActualFiles(self, input_filename, source_dir, working_dir):
     actual_paths = []
-    template_paths = self._GetTemplatePaths(
-        input_filename, source_dir, working_dir)
-    actual_path_template = template_paths[0];
-    expected_path_template = template_paths[1]
-    platform_expected_path_template = template_paths[2]
+    path_templates = PathTemplates(input_filename, source_dir, working_dir)
+
     i = 0
     while True:
-      actual_path = actual_path_template % i
-      expected_path = expected_path_template % i
-      platform_expected_path = (
-          platform_expected_path_template % (self.os_name, i))
+      actual_path = path_templates.GetActualPath(i)
+      expected_path = path_templates.GetExpectedPath(i)
+      platform_expected_path = path_templates.GetPlatformExpectedPath(
+          self.os_name, i)
       if os.path.exists(platform_expected_path):
         expected_path = platform_expected_path
       elif not os.path.exists(expected_path):
@@ -39,19 +33,16 @@
     return actual_paths
 
   def HasDifferences(self, input_filename, source_dir, working_dir):
-    template_paths = self._GetTemplatePaths(
-        input_filename, source_dir, working_dir)
-    actual_path_template = template_paths[0];
-    expected_path_template = template_paths[1]
-    platform_expected_path_template = template_paths[2]
+    path_templates = PathTemplates(input_filename, source_dir, working_dir)
+
     i = 0
     while True:
-      actual_path = actual_path_template % i
-      expected_path = expected_path_template % i
+      actual_path = path_templates.GetActualPath(i)
+      expected_path = path_templates.GetExpectedPath(i)
       # PDFium tests should be platform independent. Platform based results are
       # used to capture platform dependent implementations.
-      platform_expected_path = (
-          platform_expected_path_template % (self.os_name, i))
+      platform_expected_path = path_templates.GetPlatformExpectedPath(
+          self.os_name, i)
       if (not os.path.exists(expected_path) and
           not os.path.exists(platform_expected_path)):
         if i == 0:
@@ -75,11 +66,54 @@
       i += 1
     return False
 
-  def _GetTemplatePaths(self, input_filename, source_dir, working_dir):
+  def Regenerate(self, input_filename, source_dir, working_dir):
+    path_templates = PathTemplates(input_filename, source_dir, working_dir)
+
+    page = 0
+    while True:
+      # Loop through the generated page images. Stop when there is a page
+      # missing a png, which means the document ended.
+      actual_path = path_templates.GetActualPath(page)
+      if not os.path.isfile(actual_path):
+        break
+
+      platform_expected_path = path_templates.GetPlatformExpectedPath(
+          self.os_name, page)
+
+      # If there is a platform expected png, we will overwrite it. Otherwise,
+      # overwrite the generic png.
+      if os.path.exists(platform_expected_path):
+        expected_path = platform_expected_path
+      else:
+        expected_path = path_templates.GetExpectedPath(page)
+
+      if os.path.exists(expected_path):
+        shutil.copyfile(actual_path, expected_path)
+
+      page += 1
+
+
+ACTUAL_TEMPLATE = '.pdf.%d.png'
+EXPECTED_TEMPLATE = '_expected' + ACTUAL_TEMPLATE
+PLATFORM_EXPECTED_TEMPLATE = '_expected_%s' + ACTUAL_TEMPLATE
+
+
+class PathTemplates(object):
+
+  def __init__(self, input_filename, source_dir, working_dir):
     input_root, _ = os.path.splitext(input_filename)
-    actual_path = os.path.join(working_dir, input_root + self.ACTUAL_TEMPLATE)
-    expected_path = os.path.join(
-        source_dir, input_root + self.EXPECTED_TEMPLATE)
-    platform_expected_path = os.path.join(
-        source_dir, input_root + self.PLATFORM_EXPECTED_TEMPLATE)
-    return (actual_path, expected_path, platform_expected_path)
+    self.actual_path_template = os.path.join(working_dir,
+                                             input_root + ACTUAL_TEMPLATE)
+    self.expected_path = os.path.join(
+        source_dir, input_root + EXPECTED_TEMPLATE)
+    self.platform_expected_path = os.path.join(
+        source_dir, input_root + PLATFORM_EXPECTED_TEMPLATE)
+
+  def GetActualPath(self, page):
+    return self.actual_path_template % page
+
+  def GetExpectedPath(self, page):
+    return self.expected_path % page
+
+  def GetPlatformExpectedPath(self, platform, page):
+    return self.platform_expected_path % (platform, page)
diff --git a/testing/tools/test_runner.py b/testing/tools/test_runner.py
index 86e0563..ea8f2b8 100644
--- a/testing/tools/test_runner.py
+++ b/testing/tools/test_runner.py
@@ -81,6 +81,11 @@
     if actual_images:
       if self.image_differ.HasDifferences(input_filename, source_dir,
                                           self.working_dir):
+        if (self.options.regenerate_expected
+            and not self.test_suppressor.IsResultSuppressed(input_filename)
+            and not self.test_suppressor.IsImageDiffSuppressed(input_filename)):
+          self.image_differ.Regenerate(input_filename, source_dir,
+                                       self.working_dir)
         return False, results
     else:
       if (self.enforce_expected_images
@@ -171,12 +176,15 @@
     parser.add_option('--gold_ignore_hashes', default='', dest="gold_ignore_hashes",
                       help='Path to a file with MD5 hashes we wish to ignore.')
 
+    parser.add_option('--regenerate_expected', action="store_true", dest="regenerate_expected",
+                      help='Regenerates expected images.')
+
     parser.add_option('--ignore_errors', action="store_true", dest="ignore_errors",
                       help='Prevents the return value from being non-zero when image comparison fails.')
 
-    options, args = parser.parse_args()
+    self.options, self.args = parser.parse_args()
 
-    finder = common.DirectoryFinder(options.build_dir)
+    finder = common.DirectoryFinder(self.options.build_dir)
     self.fixup_path = finder.ScriptPath('fixup_pdf_template.py')
     self.text_diff_path = finder.ScriptPath('text_diff.py')
 
@@ -206,8 +214,8 @@
     self.test_cases = []
     self.execution_suppressed_cases = []
     input_file_re = re.compile('^.+[.](in|pdf)$')
-    if args:
-      for file_name in args:
+    if self.args:
+      for file_name in self.args:
         file_name.replace('.pdf', '.in')
         input_path = os.path.join(walk_from_dir, file_name)
         if not os.path.isfile(input_path):
@@ -233,16 +241,16 @@
 
     # Collect Gold results if an output directory was named.
     self.gold_results = None
-    if options.gold_output_dir:
+    if self.options.gold_output_dir:
       self.gold_results = gold.GoldResults('pdfium',
-                                           options.gold_output_dir,
-                                           options.gold_properties,
-                                           options.gold_key,
-                                           options.gold_ignore_hashes)
+                                           self.options.gold_output_dir,
+                                           self.options.gold_properties,
+                                           self.options.gold_key,
+                                           self.options.gold_ignore_hashes)
 
-    if options.num_workers > 1 and len(self.test_cases) > 1:
+    if self.options.num_workers > 1 and len(self.test_cases) > 1:
       try:
-        pool = multiprocessing.Pool(options.num_workers)
+        pool = multiprocessing.Pool(self.options.num_workers)
         worker_func = functools.partial(TestOneFileParallel, self)
 
         worker_results = pool.imap(worker_func, self.test_cases)
@@ -282,7 +290,7 @@
     self._PrintSummary()
 
     if self.failures:
-      if not options.ignore_errors:
+      if not self.options.ignore_errors:
         return 1
 
     return 0