trevor@media-lab.MEDIA.MIT.EDU (Trevor Darrell) (03/21/91)
As there is an obvious trade off between spatial resolution and intensity resolution in halftones, I've found that you can often do better than the default screen frequency if you know how many grey levels are in your image. (The default screen parameters imply ~32 grey levels at 300 dpi.) We have been experimenting with bits of postscript code for our images that picks a setscreen frequency based on the current device dpi, the size and scaling of the image, and the number of grey levels in the image. With the default spot function there is a lower bound on the spot frequency below which the size of the dots becomes annoying to the eye. Adobe Photoshop seems to overcome this by including resolution dependent spot functions with their images! Anyone playing with Level 1 setscreen should look at some Photoshop output... --trevor