A graphics (overlay) channel is provided with the image display.
However, it is not implemented like an image channel
but emulated in software. Only drawing functions are supported
(i.e. you cannot load an image into the overlay channel).
Three different font sizes are supported for writing text.
Fonts can be chosen via the INITIALIZE/DISPLAY command.
The currently available commands associated with the use of the overlay
channel are:
SET/OVERLAY - enable the overlay of graphics on top of the image
CLEAR/OVERLAY - disable the overlay
CLEAR/CHANNEL overlay - clear the overlay channel
DRAW/... - draw a geometric shape like CIRCLE,
RECTANGLE, etc. in the overlay plane
LABEL/DISPLAY - write a string into the overlay channel