[Scribus] Setting linescreen when printing pdf file

[Louis Desjardins]

? (At) 12h49 +0800 19/07/04, Craig Ringer ?crivait (wrote) :
>On Mon, 2004-07-19 at 05:57, Wayne Maeda wrote:
>
>  > Is it possible to print out a pdf document (with text and 
>graphics) in Windows
>>  so that the graphics print out at 75 lpi while the text remains crisp and
>  > dark black? I was under the assumption that it could be done. Most of the
>>  newspapers that I deal with request their ads to be in pdf format. They must
>  > be printing them out at a certain linescreen somehow someway.
>
>At my workplace (a newspaper) we prefer PDFs from clients. Our printer's
>RIP is what makes the decisions on linescreen, etc, and it clearly
>treats text and graphics differently. It's obvious when we've had to use
>a TIFF instead, or when a client has supplied a PDF of an image of the
>ad, because the text comes out with awful grainy edges due to the
>linescreen.

Hi Craig,
Hi Wayne,
Hi everybody,

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.

It is important to distinguish between "resolution" (dpi) and 
"linescreen" (lpi).

Please also note that it should be clear at begining that the word 
"resolution" itself covers many grounds. INPUT resolution differs 
from OUTPUT resolution and this can lead to confusion. You have 
resolution of the image file, resolution of ripping and resolution of 
output. Please read on.

RIPping implies 2 operations.

The first one being to transpose the editable code of the DTP program 
into an uneditable one, at a certain resolution in dpi. This usually 
varies from 300 dpi to 2400 dpi depending upon the software and 
material used and of course on the result needed.

Some RIPs apply the same resolution to all elements on the page. It's 
easy to understand: all elements will be ripped at the same 
resolution.

Other RIP will do what is called "dual resolution ripping". In that 
case, the rip will distinguish between vectors and will rip them at a 
high resolution such as 2400 dpi, and bitmap images will be ripped at 
300 dpi. The benefits for the workflow are lighter traffic on the 
network and faster process. A file ripped at one single high 
resolution is lots heavier than its counterpart at dual resolution. 
The reason why we can treat images at this low 300 dpi resolution is 
that images usually come at 300 dpi. So 300 dpi in, 300 dpi out. As 
for vectors, (type, vector graphics, logos, etc.), in order to 
achieve a crisp job, we need a high resolution ripping at, say, 2400 
dpi (it could be 1200 and still be OK). In anyway, the RIPping 
resolution is determinent on the end result. Keep in mind there is 
nothing absolute and it is not necessary to have dual resolution 
ripping to achieve professionnal results, nor it is better to rip at 
one single resolution. It is a matter of workflow and each has its 
benefits and drawbacks.

The second operation consist of applying a linescreen because the 
process of printing needs it to reproduce all the variations of a 
gray scale from 0% to 100%. Applied to color and with a mix of only 4 
colors, a press can reproduce what is usually being accepted as 
color-printing.

Linescreen is the trompe-l'oeil by excellence printing has lived on 
for decades. It makes the human eyes believe what they see is grey 
when it's black, and what they think is thousands of colors is only 
"4-color process" Cyan, Magenta, Yellow and Black. As per nowaday's 
standards, we can affirm there would be no printing without 
linescreen, with all the reservations this assumption implies.

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. 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". This of course has an effect on the final result. To 
avoid this, we use low linescreens. On the other hand, we need high 
linescreen to achieve a very well defined image such as in magazines 
and books of art. High resolution and high linescreen provide the 
best combination to reproduce an image at its best. (Not to forget 
good pressmen! - but I told you before there would be shortcuts!)

On top of that, the imagesetter or platesetter will also have a role 
to play in the end: the "output resolution", the grid by which the 
laser will actually expose the photosensitive material, can be 
generally set to resolutions such as 1200, 2400 or 3600 dpi. This 
output resolution determines the quality of the linescreen DOT (how 
precisely that dot is defined). Again, the smaller the grid, the 
"cleaner" the dot. The cleaner the dot, the clearer the image.

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. But don't get me wrong, since all "colors" 
will be transposed in the CMYK model, it is very important to 
consider that combination to determine if it is suitable for a tiny 
detail such as body text. For instance, if you have a green at 100% 
that will be printed using CMYK, you better be cautious on that green 
"recipe"... 80% Cyan + 80 % Yellow produce a nice Green that you may 
want to use at 100%. But the plates will contain 80% of C + 80% of Y 
and the linescreen will show its dots. If the linescreen is low, such 
as 75 or 85 lines per inch, any human eye will be able to distinguish 
the dots. At a 150 lines (the standard for magazines), it takes a 10X 
magnifier...

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.

Ugly jaggy edge I suspect is caused by an earlier manipulation in the 
process that will only be cruelly revealed by the linescreen, 
especially if it is a low one.

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%).

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). A vector element can be scaled to 
any value and will only reveal its limit at very large scale where 
the curves will show their defects if they were poorly drawn. In 
theory, if the curve is well defined, there is no limit to scaling. 
Once ripped, the vector is not vector anymore and if you enlarge it 
enough, you will see the jaggy edge of the curve line at ripping 
resolution, with the help of a good magnifier.

A poor resolution in the early stages can only be reproduced as it 
is, no matter how high we RIP and at what high value linescreen it is 
output, at which output resolution . The linescreen dot may be as 
sharp as you can imagine, if the image is pixellized... it will be 
"nicely" and "perfectly" reproduced on the film/plate, for you to 
determine in how many copies on the press.

Thank you for reading!

Louis


>
>Essentially, I'm pretty sure it's the RIP's job in a PDF workflow.
>
>>  Unfortunately, the printer that I'm dealing with currently, does 
>>not take pdf
>>  files. They want it camera ready.
>
>Heh. There aren't even any (newspaper) printers in my STATE (Western
>Australia) that accept camera ready jobs anymore. We were forced to go
>all digital, kicking and screaming, because of this - and frankly I
>would've liked to stay with our hybrid process until we could've moved
>to InDesign. Now we're stuck with Quark 4 on MacOS 9 for the forseeable
>future. (It should be pretty obvious why I'm interested in Scribus).
>
>>  Which means I have to take it to another
>  > place to have it printed out at the specified linescreen. Except that this
>>  other place does not have the software that sets the linescreen. End result:
>>  I have this pdf document with no way to print it out properly. Hmm.
>
>GhostScript appears to have some screen controls. '-dCOLORSCREEN=' and
>'-dDITHERDPI' may have some potential. I'm unable to test if they do
>what you need right now, I'm sorry, but you might want to look into
>them. They're documented briefly in 'Use.html' in the gs docs.
>
>--
>Craig Ringer
>
>
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