If what you have is something currently plotted on the screen, then you have a few choices. Probably the most convenient one is to getframe() to record the screen into a buffer and then process the resulting array.
Other possibilities including using saveas() or print() to save the screen to an image file, and then read in the image file and process the resulting array.
Another possibility includes using print() with -dmeta to record to the clipboard as a windows metadata file -- which could potentially be a vector format rather than a raster format. Processing this could potentially be a nuisance though.
