Merge pull request #66 from matthewwithanm/trimcolor-processor

Processor for trimming solid-color borders

docs/apireference.rst

@@ -18,6 +18,9 @@ API Reference
 .. automodule:: imagekit.processors.resize
   :members:
 
+.. automodule:: imagekit.processors.crop
+:members:
+
 
 :mod:`admin` Module
 --------------------

imagekit/lib.py

@@ -1,7 +1,8 @@
 # Required PIL classes may or may not be available from the root namespace
 # depending on the installation method used.
 try:
-    from PIL import Image, ImageColor, ImageChops, ImageEnhance, ImageFile, ImageFilter
+    from PIL import Image, ImageColor, ImageChops, ImageEnhance, ImageFile, \
+            ImageFilter, ImageDraw, ImageStat
 except ImportError:
     try:
         import Image
@@ -10,5 +11,7 @@ except ImportError:
         import ImageEnhance
         import ImageFile
         import ImageFilter
+        import ImageDraw
+        import ImageStat
     except ImportError:
         raise ImportError('ImageKit was unable to import the Python Imaging Library. Please confirm it`s installed and available on your current Python path.')

imagekit/processors/__init__.py

@@ -8,7 +8,7 @@ from both the filesystem and the ORM.
 
 """
 from imagekit.lib import Image, ImageColor, ImageEnhance
-from imagekit.processors import resize
+from imagekit.processors import resize, crop
 
 
 RGBA_TRANSPARENCY_FORMATS = ['PNG']

imagekit/processors/crop.py

@@ -0,0 +1,71 @@
+from ..lib import Image, ImageChops, ImageDraw, ImageStat
+
+
+class Side(object):
+    TOP = 't'
+    RIGHT = 'r'
+    BOTTOM = 'b'
+    LEFT = 'l'
+    ALL = (TOP, RIGHT, BOTTOM, LEFT)
+
+
+def crop(img, bbox, sides=Side.ALL):
+    bbox = (
+        bbox[0] if Side.LEFT in sides else 0,
+        bbox[1] if Side.TOP in sides else 0,
+        bbox[2] if Side.RIGHT in sides else img.size[0],
+        bbox[3] if Side.BOTTOM in sides else img.size[1],
+    )
+    return img.crop(bbox)
+
+
+def detect_border_color(img):
+    mask = Image.new('1', img.size, 1)
+    w, h = img.size[0] - 2, img.size[1] - 2
+    if w > 0 and h > 0:
+        draw = ImageDraw.Draw(mask)
+        draw.rectangle([1, 1, w, h], 0)
+    return ImageStat.Stat(img.convert('RGBA').histogram(mask)).median
+
+
+class TrimBorderColor(object):
+    """Trims a color from the sides of an image.
+
+    """
+    def __init__(self, color=None, tolerance=0.3, sides=Side.ALL):
+        """
+        :param color: The color to trim from the image, in a 4-tuple RGBA value,
+            where each component is an integer between 0 and 255, inclusive. If
+            no color is provided, the processor will attempt to detect the
+            border color automatically.
+        :param tolerance: A number between 0 and 1 where 0. Zero is the least
+            tolerant and one is the most.
+        :param sides: A list of sides that should be trimmed. Possible values
+            are provided by the :class:`Side` enum class.
+
+        """
+        self.color = color
+        self.sides = sides
+        self.tolerance = tolerance
+
+    def process(self, img):
+        source = img.convert('RGBA')
+        border_color = self.color or tuple(detect_border_color(source))
+        bg = Image.new('RGBA', img.size, border_color)
+        diff = ImageChops.difference(source, bg)
+        if self.tolerance not in (0, 1):
+            # If tolerance is zero, we've already done the job. A tolerance of
+            # one would mean to trim EVERY color, and since that would result
+            # in a zero-sized image, we just ignore it.
+            if not 0 <= self.tolerance <= 1:
+                raise ValueError('%s is an invalid tolerance. Acceptable values'
+                        ' are between 0 and 1 (inclusive).' % self.tolerance)
+            tmp = ImageChops.constant(diff, int(self.tolerance * 255)) \
+                    .convert('RGBA')
+            diff = ImageChops.subtract(diff, tmp)
+
+        bbox = diff.getbbox()
+        if bbox:
+            img = crop(img, bbox, self.sides)
+
+        return img