rokicki@neon.Stanford.EDU (Tomas G. Rokicki) (03/18/91)
Under Level 2 PostScript, you can get more accurate screens than the ones I talked about in my first note to this group. But that doesn't mean you should definitely use them. Accurate screens are good in many circumstances, such as color separations and the like, but they have their drawbacks as well (beyond just their computational expense.) On a low resolution device, the Level 1 screen for any gray scale will give you identical `dots' across the page---this tends to look good. With accurate screens, the dots will very; every other dot might be one pixel larger, for instance. This can create detectable patterns in what should be a single gray scale. These go away as soon as the resolution increases enough so that a single pixel enlargement in a screen `dot' is undetectable. Of course, at high resolutions, the default screens become more accurate, too. Color separation is a very tricky business, and handling the screens correctly is part of the magic. -tom
jeffhi@microsoft.UUCP (Jeff HINSCH) (03/21/91)
In article <1991Mar17.220700.19388@neon.Stanford.EDU> Tomas G. Rokicki writes: >On a low resolution device, the Level 1 screen for any gray scale will >give you identical `dots' across the page---this tends to look good. >With accurate screens, the dots will very; every other dot might be one >pixel larger, for instance. This can create detectable patterns in >what should be a single gray scale. These go away as soon as the >resolution increases enough so that a single pixel enlargement in a >screen `dot' is undetectable. Of course, at high resolutions, the >default screens become more accurate, too. I'm experiencing "detectable patterns" with Level 1--more like obvious patterns--when imaging 4-bit color Mac or Windows screens that use a dither to simulate a color. These patterns refuse to go away. I'm enormously cheered to hear that Level 2 will only compound my problems. (Using: RIP 4/L300) Jeff Hinsch -- {uunet, decvax, uw-beaver}!microsoft!jeffhi