Re: ConTeXt output & commercial printing houses: Thanks!

[Siep Kroonenberg <siepo@cybercomm.nl>]

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