Try pngquant

src/ocrmypdf/exec/pngquant.py

@@ -0,0 +1,45 @@
+# © 2018 James R. Barlow: github.com/jbarlow83
+#
+# This file is part of OCRmyPDF.
+#
+# OCRmyPDF is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# OCRmyPDF is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with OCRmyPDF.  If not, see <http://www.gnu.org/licenses/>.
+
+from subprocess import CalledProcessError, run
+from tempfile import TemporaryFile
+from functools import lru_cache
+import sys
+import os
+import shutil
+
+from . import get_version
+from ..exceptions import ExitCode
+
+
+@lru_cache(maxsize=1)
+def version():
+    return get_version('pngquant', regex=r'(\d+(\.\d+)*).*')
+
+
+def quantize(input_file, output_file, quality_min, quality_max):
+    args = [
+        'pngquant',
+        '--force',
+        '--skip-if-larger',
+        '--output', output_file,
+        '--quality', '{}-{}'.format(quality_min, quality_max),
+        '--',
+        input_file
+    ]
+    proc = run(args)
+    proc.check_returncode()

src/ocrmypdf/pipeline.py

@@ -1159,9 +1159,9 @@ def optimize_pdf(
             pikepdf.Null()
         )
 
-    # from ocrmypdf.exec import pngquant
+    from ocrmypdf.exec import pngquant
-    # for xref in pngs:
+    for xref in pngs:
-    #     pngquant.quantize(make_img_name(xref), make_img_name(xref), 65, 80)
+        pngquant.quantize(make_img_name(xref), make_img_name(xref), 65, 80)
 
     for xref in pngs:
         im_obj = pike._get_object_id(xref, 0)