Add adjust_options

This gives the user the ability to process the images after resizing them. In
particular, the color, contrast, brightness and sharpness can be adjusted.

sigal/image.py

@@ -72,6 +72,9 @@ def generate_image(source, outname, settings, options=None):
     processor = processor_cls(*settings['img_size'], upscale=False)
     img = processor.process(img)
 
+    # Adjust the image after resizing
+    img = Adjust(**settings['adjust_options']).process(img)
+
     if settings['copyright']:
         add_copyright(img, settings['copyright'])
 

sigal/settings.py

@@ -29,6 +29,8 @@ _DEFAULT_CONFIG = {
     'destination': '_build',
     'img_size': (640, 480),
     'img_processor': 'ResizeToFit',
+    'adjust_options': {'color': 1.0, 'brightness': 1.0,
+                       'contrast': 1.0, 'sharpness': 1.0},
     'make_thumbs': True,
     'thumb_prefix': '',
     'thumb_suffix': '',

sigal/templates/sigal.conf.py

@@ -26,6 +26,13 @@ img_size = (800, 600)
 # - SmartResize: identical to ResizeToFill, but uses entropy to crop the image
 # img_processor = 'ResizeToFit'
 
+# Adjust the image after resizing it. A default value of 1.0 leaves the images
+# untouched.
+# adjust_options = {'color': 1.0,
+#                   'brightness': 1.0,
+#                   'contrast': 1.0,
+#                   'sharpness': 1.0}
+
 # Generate thumbnails
 # make_thumbs = True