What do any electronically generated plots represent?
It is possible to generate files containing plot information in a variety of ways. The normal convention adopted at Compugraphics is to have any colored areas representing Clear on the mask, and the background area (either black or white) representing Dark (Chrome) areas on the photomask.
Also any plots will usually show the master mask with the chrome surface upwards.
If contact print copies were being made, this would also represent the copy photomask with the chrome surface downwards.
Any messages sent with plot files should identify the conventions used, if there is any ambiguity – please ask for clarification.