Re: ConTeXt output & commercial printing houses: Thanks!

[Brooks Moses <bmoses@stanford.edu>]

At 11:15 PM 7/26/2004, you wrote:
>On Sat, Jul 24, 2004 at 03:21:39PM -0500, Bill McClain wrote:
> > - Also, I don't know whether it is possible to downsample images in
> > PDF's that you generate from ConTeXt. If it is, avoid it.
>
>That raises an important question: if downsampling is done, is it
>obvious what ConTeXt commands cause it to happen?

There's, to my knowledge, no engine in pdfTeX for downsampling images; 
there certainly be one coded in ConTeXt.  Thus, I'd be fairly confident in 
guessing that it is indeed, fairly obvious, on grounds that there are no 
commands which do that.

> > 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