On Mon, Jul 26, 2004 at 11:33:03PM -0700, Brooks Moses wrote:
At 11:15 PM 7/26/2004, you wrote:
On Sat, Jul 24, 2004 at 03:21:39PM -0500, Bill McClain wrote:
The printer expects CMYK images (not RGB!) where the resolution is approx. 2 times the screen count in the final print, @ the physical size on the paper. So if you have an image in your PDF that is 10 cms /4 in. wide, and you want it printed in a 150 lpi (lines per inch) screen, make sure the original resolution is 300 dpi @ 10 cms / 4 in.
Now that's interesting. I imagined you would get the best results with images that were designed exactly at the printer resolution.
You might, but that would only be true if you also have the image aligned exactly with the printer resolution -- which is unlikely to be the case unless you do it explicitly. Having the 2x-or-higher resolution means that the downsampling in the printing process will produce an acceptable result no matter what the alignment is.
Beyond that, I suspect there are also some effects involved in the fact that the printer is creating a screen rather than dots of pure color; there are things going on in the screen that are on a finer scale than the line spacing, and having the higher-resolution to base them on probably produces a better result.
- Brooks
For a screened picture, you can often get away with less than twice the lpi, especially if there are no sharp transitions. On the other hand, pure black-and-white line drawings are best printed without screening. For such images, higher resolutions are better. 600dpi is enough for losing jaggies. Up to a point, more is better, but printer resolution (2400dpi or more) would produce very large bitmaps. -- Siep Kroonenberg