diff --git a/sstv/decode.py b/sstv/decode.py
index 6e74063..3d405fd 100644
--- a/sstv/decode.py
+++ b/sstv/decode.py
@@ -254,10 +254,10 @@ class SSTVDecoder(object):
                     seq_start += self._align_sync(transmission[seq_start:])
 
                 pixel_time = self.mode.PIXEL_TIME
-                if self.mode.HAS_MERGE_SCAN:
-                    # Robot mode has half-length second scan
-                    if chan % 2 == 1:
-                        pixel_time = self.mode.MERGE_PIXEL_TIME
+                if self.mode.HAS_HALF_SCAN:
+                    # Robot mode has half-length second/third scans
+                    if chan > 0:
+                        pixel_time = self.mode.HALF_PIXEL_TIME
 
                     centre_window_time = (pixel_time * window_factor) / 2
                     pixel_window = round(centre_window_time * 2 *
@@ -289,6 +289,7 @@ class SSTVDecoder(object):
 
         width = self.mode.LINE_WIDTH
         height = self.mode.LINE_COUNT
+        channels = self.mode.CHAN_COUNT
 
         image = Image.new(col_mode, (width, height))
         pixel_data = image.load()
@@ -296,21 +297,35 @@ class SSTVDecoder(object):
         log_message("Drawing image data...")
 
         for y in range(height):
-            odd_line = y % 2
 
+            odd_line = y % 2
             for x in range(width):
-                if self.mode.COLOR == spec.COL_FMT.GBR:
-                    pixel = (image_data[y][2][x],
-                             image_data[y][0][x],
-                             image_data[y][1][x])
-                elif self.mode.COLOR == spec.COL_FMT.YUV:
-                    pixel = (image_data[y][0][x],
-                             image_data[y-(odd_line-1)][1][x],
-                             image_data[y-odd_line][1][x])
-                else:
-                    pixel = (image_data[y][0][x],
-                             image_data[y][1][x],
-                             image_data[y][2][x])
+
+                if channels == 2:
+
+                    if self.mode.HAS_ALT_SCAN:
+                        if self.mode.COLOR == spec.COL_FMT.YUV:
+                            # R36
+                            pixel = (image_data[y][0][x],
+                                     image_data[y-(odd_line-1)][1][x],
+                                     image_data[y-odd_line][1][x])
+
+                elif channels == 3:
+
+                    if self.mode.COLOR == spec.COL_FMT.GBR:
+                        # M1, M2, S1, S2, SDX
+                        pixel = (image_data[y][2][x],
+                                 image_data[y][0][x],
+                                 image_data[y][1][x])
+                    elif self.mode.COLOR == spec.COL_FMT.YUV:
+                        # R72
+                        pixel = (image_data[y][0][x],
+                                 image_data[y][2][x],
+                                 image_data[y][1][x])
+                    elif self.mode.COLOR == spec.COL_FMT.RGB:
+                        pixel = (image_data[y][0][x],
+                                 image_data[y][1][x],
+                                 image_data[y][2][x])
 
                 pixel_data[x, y] = pixel
 
diff --git a/sstv/spec.py b/sstv/spec.py
index b623539..e74322f 100644
--- a/sstv/spec.py
+++ b/sstv/spec.py
@@ -34,7 +34,8 @@ class M1(object):
     WINDOW_FACTOR = 2.34
 
     HAS_START_SYNC = False
-    HAS_MERGE_SCAN = False
+    HAS_HALF_SCAN = False
+    HAS_ALT_SCAN = False
 
 
 class M2(M1):
@@ -81,7 +82,8 @@ class S1(object):
     WINDOW_FACTOR = 2.48
 
     HAS_START_SYNC = True
-    HAS_MERGE_SCAN = False
+    HAS_HALF_SCAN = False
+    HAS_ALT_SCAN = False
 
 
 class S2(S1):
@@ -121,7 +123,7 @@ class SDX(S2):
 
     LINE_TIME = SYNC_PULSE + 3 * CHAN_TIME
     PIXEL_TIME = SCAN_TIME / LINE_WIDTH
-    WINDOW_FACTOR = 1.01
+    WINDOW_FACTOR = 0.98
 
 
 class R36(object):
@@ -131,7 +133,7 @@ class R36(object):
     LINE_WIDTH = 320
     LINE_COUNT = 240
     SCAN_TIME = 0.088000
-    MERGE_SCAN_TIME = 0.044000
+    HALF_SCAN_TIME = 0.044000
     SYNC_PULSE = 0.009000
     SYNC_PORCH = 0.003000
     SEP_PULSE = 0.004500
@@ -144,16 +146,45 @@ class R36(object):
     CHAN_OFFSETS = [SYNC_PULSE + SYNC_PORCH]
     CHAN_OFFSETS.append(CHAN_OFFSETS[0] + CHAN_TIME + SEP_PORCH)
 
-    LINE_TIME = CHAN_OFFSETS[1] + MERGE_SCAN_TIME
+    LINE_TIME = CHAN_OFFSETS[1] + HALF_SCAN_TIME
     PIXEL_TIME = SCAN_TIME / LINE_WIDTH
-    MERGE_PIXEL_TIME = MERGE_SCAN_TIME / LINE_WIDTH
+    HALF_PIXEL_TIME = HALF_SCAN_TIME / LINE_WIDTH
     WINDOW_FACTOR = 7.70
 
     HAS_START_SYNC = False
-    HAS_MERGE_SCAN = True
+    HAS_HALF_SCAN = True
+    HAS_ALT_SCAN = True
+
+
+class R72(R36):
+    NAME = "Robot 72"
+
+    LINE_WIDTH = 320
+    SCAN_TIME = 0.138000
+    HALF_SCAN_TIME = 0.069000
+    SYNC_PULSE = 0.009000
+    SYNC_PORCH = 0.003000
+    SEP_PULSE = 0.004500
+    SEP_PORCH = 0.001500
+
+    CHAN_COUNT = 3
+    CHAN_TIME = SEP_PULSE + SCAN_TIME
+    HALF_CHAN_TIME = SEP_PULSE + HALF_SCAN_TIME
+
+    CHAN_OFFSETS = [SYNC_PULSE + SYNC_PORCH]
+    CHAN_OFFSETS.append(CHAN_OFFSETS[0] + CHAN_TIME + SEP_PORCH)
+    CHAN_OFFSETS.append(CHAN_OFFSETS[1] + HALF_CHAN_TIME + SEP_PORCH)
+
+    LINE_TIME = CHAN_OFFSETS[2] + HALF_SCAN_TIME
+    PIXEL_TIME = SCAN_TIME / LINE_WIDTH
+    HALF_PIXEL_TIME = HALF_SCAN_TIME / LINE_WIDTH
+    WINDOW_FACTOR = 4.88
+
+    HAS_ALT_SCAN = False
 
 
 VIS_MAP = {8: R36,
+           12: R72,
            40: M2,
            44: M1,
            56: S2,