From 61bf3ada315591207fade42888a3e1060703ccbf Mon Sep 17 00:00:00 2001
From: Oliver Tonnhofer <olt@bogosoft.com>
Date: Fri, 20 May 2016 12:00:05 +0200
Subject: [PATCH] convert src images to RGBA if band merge requires alpha band

---
 mapproxy/image/merge.py          | 16 ++++++++++++++--
 mapproxy/test/unit/test_image.py | 24 +++++++++++++++++++++++-
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/mapproxy/image/merge.py b/mapproxy/image/merge.py
index 82751c6be..7b40a2cd6 100644
--- a/mapproxy/image/merge.py
+++ b/mapproxy/image/merge.py
@@ -148,6 +148,7 @@ def __init__(self, mode=None):
         self.ops = []
         self.cacheable = True
         self.mode = mode
+        self.max_band = {}
 
     def add_ops(self, dst_band, src_img, src_band, factor=1.0):
         self.ops.append(band_ops(
@@ -156,6 +157,8 @@ def add_ops(self, dst_band, src_img, src_band, factor=1.0):
             src_band=src_band,
             factor=factor,
          ))
+        # store highest requested band index for each source
+        self.max_band[src_img] = max(self.max_band.get(src_img, 0), src_band)
 
     def merge(self, sources, image_opts, size=None, bbox=None, bbox_srs=None, coverage=None):
         if not sources:
@@ -166,10 +169,19 @@ def merge(self, sources, image_opts, size=None, bbox=None, bbox_srs=None, covera
 
         # load src bands
         src_img_bands = []
-        for layer_img in sources:
+        for i, layer_img in enumerate(sources):
             img = layer_img.as_image()
-            if img.mode == 'P':
+
+            if i not in self.max_band:
+                # do not split img if not requested by any op
+                src_img_bands.append(None)
+                continue
+
+            if self.max_band[i] == 3 and img.mode != 'RGBA':
+                # convert to RGBA if band idx 3 is requestd (e.g. P or RGB src)
                 img = img.convert('RGBA')
+            elif img.mode == 'P':
+                img = img.convert('RGB')
             src_img_bands.append(img.split())
 
         tmp_mode = self.mode
diff --git a/mapproxy/test/unit/test_image.py b/mapproxy/test/unit/test_image.py
index 001ae3dcf..8435834e2 100644
--- a/mapproxy/test/unit/test_image.py
+++ b/mapproxy/test/unit/test_image.py
@@ -733,4 +733,26 @@ def test_from_p_merge(self):
 
         img = result.as_image()
         eq_(img.mode, 'RGB')
-        eq_(img.getpixel((0, 0)), (200, 100, 0))
\ No newline at end of file
+        eq_(img.getpixel((0, 0)), (200, 100, 0))
+
+    def test_from_mixed_merge(self):
+        """
+        Check merge RGBA bands from image without alpha (mixed)
+        """
+        merger = BandMerger(mode='RGBA')
+
+        merger.add_ops(dst_band=0, src_img=0, src_band=2)
+        merger.add_ops(dst_band=1, src_img=0, src_band=1)
+        merger.add_ops(dst_band=2, src_img=0, src_band=0)
+        merger.add_ops(dst_band=3, src_img=0, src_band=3)
+
+        img = Image.new('RGB', (10, 10), (0, 100, 200))
+        src_img = ImageSource(img)
+
+        img_opts = ImageOptions('RGBA')
+        result = merger.merge([src_img], img_opts)
+
+        img = result.as_image()
+        eq_(img.mode, 'RGBA')
+        eq_(img.getpixel((0, 0)), (200, 100, 0, 255))
+