Ghostscript interprets PostScript programs and renders the graphics that they output. The resulting output image is invariably device dependent. Indeed, the original PostScript file is the device independent form of the image.
Even though the images that Ghostscript renders can be saved in PICT files or on the clipboard in PICT format, these are still device dependent versions of the image: they will not scale well, nor will they display well with different numbers of available colors. These PICT images are simply pixel graphics, not object-oriented graphics. (If you examine these PICT files in a graphics program, you will notice that they are just a single large pixel map.)
The Macintosh device currently renders to any of the following characteristics (which you control in the Settings dialog):
72 dpi
1, 4, or 8 bits per pixel
standard Macintosh palettes for 4-bit gray, or 8-bit color
These choices must be made at the time Ghostscript renders an image so that Ghostscript can do its best. For example, Ghostscript will use halftone screens to achieve colors not in the palette.
Though the scaling options may change the dpi from the point of view of the PostScript program, the resulting image on the screen (obviously, as we can't change your hardware on the fly!) and as saved in a PICT file, is 72dpi. For example: If you choose a scaling option of a "Third", the PostScript program appears to render on a 24dpi device, as 24 pixels make up an inch. On the screen, however, 24 pixels make up a third of an inch at 72dpi, thus achieving the 'Third' scaling factor.
The standard Macintosh 8-bit palette is a color cube of 6x6x6 values in RGB space. In addition, it adds evenly spaced ramps of 16 values each of red, green, blue, and gray. Using this palette allows Ghostscript to render with out having the change the palette of a normal 8-bit display system.
