Improved the RGB endpoint by allowing more dynamic scaling and making…

… the alpha channel optional.

CHANGELOG.rst

@@ -1,6 +1,12 @@
 django-raster change log
 ========================
 
+0.6
+---
+* Changed alpha channel handling on RGB endpoint. The alpha channel is now
+  switched off by default. To activate it, add the ``alpha`` query parameter
+  to the rgb request.
+
 0.5
 ---
 * Added ``memory_efficient`` flag to value count aggregator. The value counts

docs/algebra.rst

@@ -96,11 +96,15 @@ If the raw data in the tiles is not already scaled to the range [0, 255], an
 additional scaling factor can be specified, which will be used to rescale
 all three bands to the default RGB color range. For instance, the following
 query would assume that the input bands have values in the range of
-[0, 10000], and would rescale them to the RGB color space.
+[5, 10000], and would rescale them to the RGB color space.
 
 ::
 
-    /raster/algebra/{z}/{x}/{y}.png?layers=r=1,g=3,b=6&scale=1e4
+    /raster/algebra/{z}/{x}/{y}.png?layers=r=1,g=3,b=6&scale=5,10000
+
+An alpha channel can be activated by passing the ``alpha`` query parameter. The
+alpha parameter makes all the pixels transparent that have values equal to
+``0`` in all three RGB channels.
 
 Formula parser
 --------------

raster/views.py

@@ -254,24 +254,49 @@ def get_rgb(self, data):
         green = green.bands[0].data()
         blue = blue.bands[0].data()
 
-        scale = float(self.request.GET.get('scale', 255))
-
-        red[red > scale] = scale
-        green[green > scale] = scale
-        blue[blue > scale] = scale
-
-        red = red * 255.0 / scale
-        green = green * 255.0 / scale
-        blue = blue * 255.0 / scale
-
-        # Create zeros array.
-        alpha = 255 * (red > 0) * (blue > 0) * (green > 0)
+        # Get scale for the image value range.
+        if 'scale' in self.request.GET:
+            # The scale is either a number or two numbers separated by comma.
+            scale = self.request.GET.get('scale').split(',')
+            if len(scale) == 1:
+                scale_min = 0
+                scale_max = float(scale[0])
+            else:
+                # Get min an max scale from
+                scale_min = float(scale[0])
+                scale_max = float(scale[1])
+
+                # Clip the image minimum.
+                red[red < scale_min] = scale_min
+                green[green < scale_min] = scale_min
+                blue[blue < scale_min] = scale_min
+
+            # Clip the image maximum.
+            red[red > scale_max] = scale_max
+            green[green > scale_max] = scale_max
+            blue[blue > scale_max] = scale_max
+
+            # Scale the image.
+            red = 255 * (red - scale_min) / scale_max
+            green = 255 * (green - scale_min) / scale_max
+            blue = 255 * (blue - scale_min) / scale_max
+
+        if 'alpha' in self.request.GET:
+            mode = 'RGBA'
+            reshape = 4
+            # Create the alpha channel.
+            alpha = 255 * (red > 0) * (blue > 0) * (green > 0)
+            img_array = numpy.array((red.ravel(), green.ravel(), blue.ravel(), alpha.ravel()))
+        else:
+            mode = 'RGB'
+            reshape = 3
+            img_array = numpy.array((red.ravel(), green.ravel(), blue.ravel()))
 
-        rgba = numpy.array((red.ravel(), green.ravel(), blue.ravel(), alpha.ravel())).T
-        rgba = rgba.reshape(WEB_MERCATOR_TILESIZE, WEB_MERCATOR_TILESIZE, 4).astype('uint8')
+        # Reshape array into tile size.
+        img_array = img_array.T.reshape(WEB_MERCATOR_TILESIZE, WEB_MERCATOR_TILESIZE, reshape).astype('uint8')
 
         # Create image from array
-        img = Image.fromarray(rgba)
+        img = Image.fromarray(img_array, mode=mode)
         stats = {}
 
         # Return rendered image

tests/test_algebra.py

@@ -130,3 +130,5 @@ def test_band_level_algebra_request(self):
     def test_rgb_request(self):
         response = self.client.get(self.algebra_tile_url + '?layers=r={0},g={0},b={0}'.format(self.rasterlayer.id))
         self.assertEqual(response.status_code, 200)
+        response = self.client.get(self.algebra_tile_url + '?layers=r={0},g={0},b={0}&alpha'.format(self.rasterlayer.id))
+        self.assertEqual(response.status_code, 200)