img: add Png.horz_dpi

Steve Canny · Steve Canny · commit 17866e3104c1 · 2014-02-27T12:08:34.000-08:00
diff --git a/docx/image/png.py b/docx/image/png.py
@@ -39,6 +39,22 @@ def from_stream(cls, stream, blob, filename):
         cx, cy = attrs.pop('px_width'), attrs.pop('px_height')
         return Png(blob, filename, cx, cy, attrs)
 
+    @property
+    def horz_dpi(self):
+        """
+        Integer dots per inch for the width of this image. Defaults to 72
+        when not present in the file, as is often the case.
+        """
+        units_specifier = self._attrs.get(TAG.UNITS_SPECIFIER)
+        horz_px_per_unit = self._attrs.get(TAG.HORZ_PX_PER_UNIT)
+
+        if units_specifier == 1 and horz_px_per_unit is not None:
+            horz_dpi = int(round(horz_px_per_unit * 0.0254))
+        else:
+            horz_dpi = 72
+
+        return horz_dpi
+
     @classmethod
     def _parse_png_headers(cls, stream):
         """
diff --git a/features/img-characterize-image.feature b/features/img-characterize-image.feature
@@ -15,4 +15,4 @@ Feature: Characterize an image file
 
    Examples: Image file characteristics
      | filename | mime_type | cx  |  cy  | horz_dpi | vert_dpi |
-     | test.png | image/png | 901 | 1350 |   333    |   444    |
+     | test.png | image/png | 901 | 1350 |   150    |   444    |
diff --git a/tests/image/test_png.py b/tests/image/test_png.py
@@ -71,6 +71,10 @@ def it_can_parse_an_pHYs_chunk(self, parse_pHYs_fixture):
         attrs = Png._parse_pHYs(stream, offset)
         assert attrs == expected_attrs
 
+    def it_knows_its_horizontal_dpi(self, horz_dpi_fixture):
+        png, expected_horz_dpi = horz_dpi_fixture
+        assert png.horz_dpi == expected_horz_dpi
+
     # fixtures -------------------------------------------------------
 
     @pytest.fixture
@@ -120,6 +124,19 @@ def from_stream_fixture(
             stream_rdr_, Png__init__, cx, cy, attrs, png_
         )
 
+    @pytest.fixture(params=[
+        (5906, 1, 150), (11811, 1, 300), (5906, 0, 72), (None, 0, 72),
+        (666, 0, 72), (2835, 1, 72)
+    ])
+    def horz_dpi_fixture(self, request):
+        horz_px_per_unit, units_specifier, expected_horz_dpi = request.param
+        attrs = {
+            TAG.HORZ_PX_PER_UNIT: horz_px_per_unit,
+            TAG.UNITS_SPECIFIER:  units_specifier
+        }
+        png = Png(None, None, None, None, attrs)
+        return png, expected_horz_dpi
+
     @pytest.fixture
     def no_IHDR_fixture(self, stream_, chunk_offsets):
         return stream_, chunk_offsets
