Add watermark plugin

AUTHORS

@@ -8,3 +8,4 @@ alphabetical order):
 - Matthias Vogelgesang
 - Vikram Shirgur
 - Yuce Tekol
+- Abdul Qabiz

docs/plugins.rst

@@ -103,3 +103,8 @@ Upload to S3 plugin
 ===================
 
 .. automodule:: sigal.plugins.upload_s3
+
+Watermark plugin
+===================
+
+.. automodule:: sigal.plugins.watermark

sigal/plugins/watermark.py

@@ -0,0 +1,77 @@
+# -*- coding: utf-8 -*-
+
+"""Plugin which adds a watermark to the image.
+
+Settings:
+
+- ``watermark``: path to the watermark image.
+- ``watermark_position``: the watermark position (scale or tile)
+- ``watermark_opacity``: the watermark opacity (0.0 to 1.0)
+
+"""
+
+## Original code: http://code.activestate.com/recipes/362879-watermark-with-pil/
+
+import logging
+from PIL import ImageDraw, Image, ImageEnhance
+from sigal import signals
+
+logger = logging.getLogger(__name__)
+
+
+def reduce_opacity(im, opacity):
+    """Returns an image with reduced opacity."""
+    assert opacity >= 0 and opacity <= 1
+    if im.mode != 'RGBA':
+        im = im.convert('RGBA')
+    else:
+        im = im.copy()
+    alpha = im.split()[3]
+    alpha = ImageEnhance.Brightness(alpha).enhance(opacity)
+    im.putalpha(alpha)
+    return im
+
+def watermark(im, mark, position, opacity=1):
+    """Adds a watermark to an image."""
+    if opacity < 1:
+        mark = reduce_opacity(mark, opacity)
+    if im.mode != 'RGBA':
+        im = im.convert('RGBA')
+    # create a transparent layer the size of the image and draw the
+    # watermark in that layer.
+    layer = Image.new('RGBA', im.size, (0,0,0,0))
+    if position == 'tile':
+        for y in range(0, im.size[1], mark.size[1]):
+            for x in range(0, im.size[0], mark.size[0]):
+                layer.paste(mark, (x, y))
+    elif position == 'scale':
+        # scale, but preserve the aspect ratio
+        ratio = min(
+            float(im.size[0]) / mark.size[0], float(im.size[1]) / mark.size[1])
+        w = int(mark.size[0] * ratio)
+        h = int(mark.size[1] * ratio)
+        mark = mark.resize((w, h))
+        layer.paste(mark, ((im.size[0] - w) / 2, (im.size[1] - h) / 2))
+    else:
+        layer.paste(mark, position)
+    # composite the watermark with the layer
+    return Image.composite(layer, im, layer)
+
+def add_watermark(img, settings=None):
+    logger.debug('Adding watermark to %r', img)
+    mark = Image.open(settings['watermark'])
+    position = 'scale'
+    opacity = 1
+    if settings['watermark_position']:
+        position = settings['watermark_position']
+    if settings['watermark_opacity']:
+        opacity = settings["watermark_opacity"]
+
+    return watermark(img, mark, position, opacity)
+
+
+def register(settings):
+    if settings.get('watermark'):
+        signals.img_resized.connect(add_watermark)
+    else:
+        logger.warning('Watermark image is not set')

tests/sample/sigal.conf.py

@@ -10,10 +10,12 @@ keep_orig = True
 links = [('Example link', 'http://example.org'),
          ('Another link', 'http://example.org')]
 
-plugins = ['sigal.plugins.adjust', 'sigal.plugins.copyright']
+plugins = ['sigal.plugins.adjust', 'sigal.plugins.copyright', 'sigal.plugins.watermark']
 copyright = u"© An example copyright message"
 adjust_options = {'color': 0.0, 'brightness': 1.0,
                   'contrast': 1.0, 'sharpness': 0.0}
-
+watermark = "watermark.png"
+watermark_position = "tile"
+watermark_opacity = 0.3
 # theme = 'galleria'
 # thumb_size = (280, 210)