utils: raspberrypi: ctt: Fix alsc green averaging

The alsc component of ctt meant to average the two green channels into
one, but used incorrect indexing resulting in only the first green
channel being used. Fix this.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: David Plowman <david.plowman@raspberrypi.com>

utils/raspberrypi/ctt/ctt_alsc.py

@@ -132,7 +132,7 @@ def alsc(Cam, Img, do_alsc_colour, plot=False):
     """
     average the green channels into one
     """
-    av_ch_g = np.mean((channels[1:2]), axis=0)
+    av_ch_g = np.mean((channels[1:3]), axis=0)
     if do_alsc_colour:
         """
         obtain 16x12 grid of intensities for each channel and subtract black level