ghostscript: remove unnecessary post-render resizing step

src/ocrmypdf/exec/ghostscript.py

@@ -129,8 +129,7 @@ def rasterize_pdf(
     :param filter_vector: if True, remove vector graphics objects
     :return:
     """
-    res = xres, yres
-    int_res = round(xres), round(yres)
+    res = round(xres, 6), round(yres, 6)
     if not page_dpi:
         page_dpi = res
 
@@ -145,7 +144,7 @@ def rasterize_pdf(
                 f'-sDEVICE={raster_device}',
                 f'-dFirstPage={pageno}',
                 f'-dLastPage={pageno}',
-                f'-r{str(int_res[0])}x{str(int_res[1])}',
+                f'-r{res[0]:f}x{res[1]:f}',
             ]
             + (['-dFILTERVECTOR'] if filter_vector else [])
             + [
@@ -168,23 +167,8 @@ def rasterize_pdf(
             log.error('Ghostscript rasterizing failed')
             raise SubprocessOutputError()
 
-        # Ghostscript only accepts integers for output resolution
-        # if the resolution happens to be fractional, then the discrepancy
-        # would change the size of the output page, especially if the DPI
-        # is quite low. Resize the image to the expected size
-
         tmp.seek(0)
         with Image.open(tmp) as im:
-            expected_size = (
-                round(im.size[0] / int_res[0] * res[0]),
-                round(im.size[1] / int_res[1] * res[1]),
-            )
-            if expected_size != im.size or page_dpi != (xres, yres):
-                log.debug(
-                    f"Ghostscript: resize output image {im.size} -> {expected_size}"
-                )
-                im = im.resize(expected_size)
-
             if rotation is not None:
                 log.debug("Rotating output by %i", rotation)
                 # rotation is a clockwise angle and Image.ROTATE_* is

tests/test_ghostscript.py

@@ -0,0 +1,81 @@
+# © 2019 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/>.
+
+import logging
+from decimal import Decimal
+
+import pikepdf
+import pytest
+from PIL import Image
+
+from ocrmypdf.exec.ghostscript import rasterize_pdf
+
+
+@pytest.fixture
+def linn(resources):
+    path = resources / 'linn.pdf'
+    return path, pikepdf.open(path)
+
+
+def test_rasterize_size(linn, outdir, caplog):
+    path, pdf = linn
+    page_size_pts = (pdf.pages[0].MediaBox[2], pdf.pages[0].MediaBox[3])
+    assert pdf.pages[0].MediaBox[0] == pdf.pages[0].MediaBox[1] == 0
+    page_size = (page_size_pts[0] / Decimal(72), page_size_pts[1] / Decimal(72))
+    target_size = Decimal('200.0'), Decimal('150.0')
+    target_dpi = 42.0, 4242.0
+
+    log = logging.getLogger()
+    rasterize_pdf(
+        path,
+        outdir / 'out.png',
+        target_size[0] / page_size[0],
+        target_size[1] / page_size[1],
+        raster_device='pngmono',
+        log=log,
+        page_dpi=target_dpi,
+    )
+
+    with Image.open(outdir / 'out.png') as im:
+        assert im.size == target_size
+        assert im.info['dpi'] == target_dpi
+
+
+def test_rasterize_rotated(linn, outdir, caplog):
+    path, pdf = linn
+    page_size_pts = (pdf.pages[0].MediaBox[2], pdf.pages[0].MediaBox[3])
+    assert pdf.pages[0].MediaBox[0] == pdf.pages[0].MediaBox[1] == 0
+    page_size = (page_size_pts[0] / Decimal(72), page_size_pts[1] / Decimal(72))
+    target_size = Decimal('200.0'), Decimal('150.0')
+    target_dpi = 42.0, 4242.0
+
+    log = logging.getLogger()
+    caplog.set_level(logging.DEBUG)
+    rasterize_pdf(
+        path,
+        outdir / 'out.png',
+        target_size[0] / page_size[0],
+        target_size[1] / page_size[1],
+        raster_device='pngmono',
+        log=log,
+        page_dpi=target_dpi,
+        rotation=90,
+    )
+
+    with Image.open(outdir / 'out.png') as im:
+        assert im.size == (target_size[1], target_size[0])
+        assert im.info['dpi'] == (target_dpi[1], target_dpi[0])