[Scribus] Setting linescreen when printing pdf file

[Craig Ringer]

On Wed, 2004-07-21 at 10:44, Louis Desjardins wrote:

> This is an interesting discussion. I apologize in advance for all the 
> shortcuts in the following answer; we could write a book on that 
> subject.

No worries. Your message is really interesting - I'm the IT guy at my
paper, and I don't know anywhere near as much about print as I'd like to
(and probably should).

> Linescreen may vary from 15 line per inch (lpi) to 200 lpi and even 
> much higher on high-end systems. You can apply a low or a high 
> linescreen to a high resolution file, and vice-versa.

Though a high line screen on a low-res file will get you a result where
pixellation or scaling artifacts are really obvious, yes?

Also, with a low line screen my understanding is that a high-res input
doesn't do you any good, because it's not possible to represent the
additional information in the coarse output.

> Various 
> combinations, various results. For a newspaper, printed on a 
> high-speed web press on cheap, uncoated, newsprint paper, the need 
> for a low linescreen is obvious. You don't want ink to "plug" your 
> images, so you need big dots spaced by lots of space because this 
> paper will allow ink to penetrate deeply into its fibers and 
> "spreading".

Yep. We get 30% dot gain here (!!) due to the way the paper bleeds so
much. My understanding is that you can't use a fine screen without
everything mashing together and producing muddy, soggy, awful images. 

> So yes, absolutely, the linescreen is applied to the entire page. To 
> what extent does it affect the elements? First, there are no "dots" 
> to see in a 100% of any of the CMYK color since the whole area is 
> filled with that color.

Can any press actually handle 100%, though? We're limited to 98%
pure-black, ~96% CMKY here.

> Linescreen is a necessity, it is not evil. ALL printed material is 
> screened. A 150-lines job can be of very high quality. Even newspaper 
> don't look so bad.

Sometimes ;-)

Depends a _lot_ on your press, and the skill of the press staff. We used
to have some pretty awful results, but now we get very nice photos when
we use good near-white stock - better than a cheap home inkjet
sometimes.

> A TIFF image has a fixed resolution. It can be anything. Usually, 72, 
> 150, 300, 600 dpi. This depends on the scanner settings or the 
> settings at which the image was saved. If the TIFF's resolution is 
> too low, there is no way this image will produce good result on a 
> press. Also, if the black generation came from the RGB world, as I 
> wrote in an earlier message, that black may not be black only and 
> could end up beeing 5% or 7% short of a full 100% black. Then, of 
> course, it will be screened and of course if it is too small an 
> element, low (and even high) linescreen will reveal the weekness of 
> the whole process if that element is not "solid" ink (100%).

Hmm. It could be, then, that when clients supply us with ads in TIFF
format (or PDFs that contain only an image), Acrobat or something at the
printer's is downsampling the image, causing the quality issues - and
that if we sent the image at a high resolution (say, >800dpi) we might
get better results.

This bears thinking about. Unfortunately, it might be quite tricky to
downsample _most_ of the graphics on the page, but leave any ads
untouched. Hmm. This is something I need to look into, anyway.

> A PDF is a vector file and has no predefined resolution until it is 
> actually ripped (fixed). Only, the pictures in the PDF can be 
> converted, at PDF creation, to a specific resolution (this is why the 
> graphic art industry has come up with specifications such as 
> PDF/X-1a, to avoid unusable PDFs).

Clients? Follow specs? What a lovely thought. Maybe it'll happen one day
;-)

> Thank you for reading!

Thank /you/ for your very helpful post. I'm familiar with most of what
you write here, but not in as much detail or as solidly as I'd like, so
it's very helpful.

--
Craig Ringer