Add a class for generating thumbnails using PIL

synapse/media/v1/thumbnailer.py

@@ -0,0 +1,78 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import PIL.Image
+
+class Thumbnailer(object):
+
+    FORMAT_JPEG="JPEG"
+    FORMAT_PNG="PNG"
+
+    def __init__(self, input_path):
+        self.image = PIL.Image.open(input_path)
+        self.width, self.height = self.image.size
+
+    def size_preserve(self, max_width, max_height):
+        """Calculate the largest size that preserves aspect ratio which
+        fits within the given rectangle::
+
+            (w_in / h_in) = (w_out / h_out)
+            w_out = min(w_max, h_max * (w_in / h_in))
+            h_out = min(h_max, w_max * (h_in / w_in))
+
+        Args:
+            max_width: The largest possible width.
+            max_height: The larget possible height.
+        """
+
+        if max_width * self.height < max_height * self.width:
+            return (max_width, (max_width * self.height) // self.width)
+        else:
+            return ((max_height * self.width) // self.height, max_height)
+
+    def thumbnail_scale(self, output_path, output_format, width, height):
+        """Rescales the image to the given dimensions"""
+        output = self.image.resize((width, height), PIL.Image.BILINEAR)
+        output.save(output_path, output_format)
+
+    def thumbnail_crop(self, output_path, output_format, width, height):
+        """Rescales and crops the image to the given dimensions preserving
+        aspect::
+            (w_in / h_in) = (w_scaled / h_scaled)
+            w_scaled = max(w_out, h_out * (w_in / h_in))
+            h_scaled = max(h_out, w_out * (h_in / w_in))
+
+        Args:
+            max_width: The largest possible width.
+            max_height: The larget possible height.
+        """
+        if width * self.height > height * self.width:
+            scaled_height = (width * self.height) // self.width
+            scaled_image = self.image.resize(
+                (width, scaled_height), PIL.Image.BILINEAR
+            )
+            crop_top = (scaled_height - height) // 2
+            crop_bottom = height + crop_top
+            cropped = scaled_image.crop((0, crop_top, width, crop_bottom))
+            cropped.save(output_path, output_format)
+        else:
+            scaled_width = (height * self.width) // self.height
+            scaled_image = self.image.resize(
+                (scaled_width, height), PIL.Image.BILINEAR
+            )
+            crop_left = (scaled_width - width) // 2
+            crop_right = width + crop_left
+            cropped = scaled_image.crop((crop_left, 0, crop_right, height))
+            cropped.save(output_path, output_format)