RE: ConTeXt output & commercial printing houses: Thanks!

["Mats Broberg" <mats.broberg@arsimprimispress.com>]

> From: ntg-context-bounces@ntg.nl 
> [mailto:ntg-context-bounces@ntg.nl] On Behalf Of Matt Gushee

> Well, yes. Many printers here do prefer PDF. However, there's 
> a small problem in some cases--I know this is true for 
> Kinko's, and was wondering if it's true for regular printers, 
> too: they think that PDF means "Adobe PDF"--i.e. they believe 
> that Adobe software is *the* way to produce PDF, and are 
> mostly unaware that there is such a thing as a PDF standard. 
> Now, I don't fully understand the issue, but apparently Adobe 
> software doesn't entirely follow the published specs, whereas 
> TeX does. And some processing software seems to be designed 
> specifically to work with the quirks of Acrobat output, and 
> sometimes has trouble with PDFTeX output.

At one of the company I work for, we generate thousands of press-ready
PDF manuals (250+ pp each) every year that are generated from XML source
using XEP from RenderX - with no problems at all. So I don't think it is
a requirement for printers that the PDF files are generated using Adobe
tools.

> Now that's interesting. I imagined you would get the best 
> results with images that were designed exactly at the printer 
> resolution.

True, for line art - but the "exactness" is unimportant. A common
imagesetter resolution is 2540 lpi, so you may want to create your line
art in that resolution. However, most printers prefer 1200 dpi (but not
less) for line art, since images with a higher resolution become so
large (memory-wise).

Regarding halftones (color or grayscale), the commercial printing
community rule-of-thumb is a resolution about 2 times the screen count.
If your image is 10 cm wide on the scanner and you want it to be 10 cm
wide on the paper, and you want the printer use a screen of 150 lpi,
scan it at an optical resolution of 300 dpi. However, as I mentioned
before, this holds true only if the physical image size and the final
image size are the same. If the image is 5 cm wide on the scanner and
you want it to be 10 cms wide on the paper, you need to scan it with a
resolution of 600 dpi.

Never increase the resolution of an already scanned image using software
interpolation.

Regarding using a higher resolution than 2-2.5 times the screen count,
try to avoid it, since the photomechanical laws of process engraving
doesn't give you a better final image anyway. However, pls note that I
am talking about conventional lito offset here, and that I am talking
about a conventional screen technology (amplitude-modulated screening).
If you are using waterless lito offset, the screen count is usually
quite a bit higher (300-500 lpi are not uncommon), which requires higher
resolutions. Also, if you are using a different screening technology -
e.g. frequency-modulated screening, or a hybride screening - your images
may need to be of a higher resolution too. Talk to your printer.

Best regards,
Mats Broberg