Direct support for grayscale images.
Direct support for grayscale images.

Grayscale images are interpreted by VisionBonnet as RGB where all
channels are the same. This is just an optimization to send 3 times less
data over SPI.

Change-Id: I0322cbff8381f295772b1eadead0a4d0d7f335fc

google/aiyprojects-raspbian,google/aiyprojects-raspbian,google/aiyprojects-raspbian,google/aiyprojects-raspbian,google/aiyprojects-raspbian