Merge pull request #36 from NaturalHistoryMuseum/feature/35-resize-mi…

…nimum

Feature/35 resize minimum

CHANGELOG.md

@@ -1,3 +1,6 @@
+# v0.1.13
+- #35 resize strategy minimum
+
 # v0.1.12
 - #33 decode_barcodes csv error
 

gouda/strategies/resize.py

@@ -10,23 +10,38 @@ def _unsharpmask(img):
     return cv2.addWeighted(img, 3, blur, -2, 0)
 
 
-def resize(img, engine):
+
+def resize(img, engine, minimum_pixels=10):
     # Entire image at different fractions of original size
 
+    # Minimum number of pixel along each edge.
+    if minimum_pixels < 3:
+        raise ValueError('Invalid value for minimum_pixels: [{0}]'.format(
+            minimum_pixels
+        ))
+
     # TODO LH try more sharpening, equalisation, other stuff?
     for sharpening in (0, 1, 2):
         if sharpening > 0:
             img = _unsharpmask(img)
-        for f in [round(x * 0.01, 2) for x in range(100, 0, -5)]:
+        height, width = img.shape[1], img.shape[0]
+        for factor in [round(x * 0.01, 2) for x in range(100, 0, -5)]:
             msg = 'resize: scaling factor [{0}] sharpening [{1}]'
-            msg = msg.format(f, sharpening)
+            msg = msg.format(factor, sharpening)
             debug_print(msg)
-            if 1 == f:
-                i = img
+            if 1 == factor:
+                resized = img
             else:
-                # Resize from the original image
-                i = cv2.resize(img, (0, 0), fx=f, fy=f)
-            barcodes = engine(i)
+                # Resize from the original image, only if resized height and
+                # width are greater than the minimum.
+                # cv2.resize raises an error if either dimension is zero.
+                dsize = (int(round(height * factor)), int(round(width * factor)))
+                if dsize[0] >= minimum_pixels and dsize[1] >= minimum_pixels:
+                    resized = cv2.resize(img, dsize)
+                else:
+                    # No point in continuing to shrink
+                    break
+            barcodes = engine(resized)
             if barcodes:
                 return msg, barcodes
 

gouda/tests/test_strategies.py

@@ -64,8 +64,6 @@ def test_1d_roi(self):
 
     @unittest.skipUnless(DM_ENGINE,
                          'No available engine for reading Data Matrix codes')
-    @unittest.skipUnless(hasattr(cv2, 'createCLAHE'),
-                         'Older cv2 without createCLAHE')
     def test_dm_resize(self):
         self._test_dm(resize)
 
@@ -90,6 +88,25 @@ def test_no_barcode_roi(self):
         img = cv2.imread(str(TESTDATA / 'nobarcode.png'))
         self.assertIsNone(roi(img, self.ONED_ENGINE))
 
+    @unittest.skipUnless(DM_ENGINE or ONED_ENGINE,
+                         'No available engine')
+    def test_resize_minimum_value(self):
+        img = cv2.imread(str(TESTDATA / 'nobarcode.png'))
+        engine = self.DM_ENGINE if self.DM_ENGINE else self.ONED_ENGINE
+        self.assertRaises(ValueError, resize, img, engine, minimum_pixels=0)
+
+    @unittest.skipUnless(DM_ENGINE or ONED_ENGINE,
+                         'No available engine')
+    def test_resize_tiny_image(self):
+        "The resize strategy is given a very small image with no barcode"
+        # Test that the resize strategy can cope with very small images without
+        # cv2.resize raising an error
+        img = cv2.imread(str(TESTDATA / 'nobarcode.png'))
+        img = img[0:10, 0:10]
+        engine = self.DM_ENGINE if self.DM_ENGINE else self.ONED_ENGINE
+        self.assertIsNone(resize(img, engine))
+        self.assertIsNone(resize(img, engine, minimum_pixels=3))
+
 
 if __name__ == '__main__':
     unittest.main()