[atlantaprog] Re: CD Booklet / Layout

>Do pdfs have resolution like raster art, or are they independent like
>vector art?

PDF stands for "Portable document format". The are vector AND raster. 
Fints and line-art graphics are handled as vectors, while photos and 
other raster images are generally handled at whatever resolution they 
were saved with.

>Whoa, wait a minute...  A tiff file is fixed at whatever you saved it
>as.  Don't confuse people who have no clue what we are talking about and
>are trying to learn.  It's not like tiffs are ALWAYS 300 dpi and can
>never be anything else!
>  We created this as a 600 dpi tiff file. There was no blurring of 
>edges present at all

True, tiffs are whatever resolution you save them as. The problem 
comes in when you have very small text that is built out of several 
process colors - or knocks out of several colors... in this case, 
even 600 dpi is not sufficient resolution to guarantee that the edges 
won't break up if the printing plates get slightly out of alignment 
(a common occurrence). Imagesetters rasterize vector graphics (incl. 
fonts) to whatever resolution they are set for, typically 2400 dpi 
(dots per inch).

Another factor is line screen, typically 150 or 133. The is the 
formula that's used to calculate the process color "dots" you see 
when you look at printed photos up close. The line screen you use is 
determined by the "dot gain" of your paper. This is how much the ink 
will "spread" when it hits the paper. Coated magazine-type stock can 
take 133-150 lines per inch, while newsprint and coarse cardboard can 
only take about 70 or 80 before the start closing up and looking like 
a mess! Your photo resolution should be twice your line screen. Any 
additional resolution is ignored by the imagesetters. The colors you 
use can make a big difference... text knocked out of solid black or 
another solid color may look fine at even 300 dpi, while an orange or 
purple or brown that's built out of high proportions of several 
process colors can create big-time fuzzy edges if/when the plates 
lose alignment.

Trapping is another factor. Trapping is the method that printers use 
to insure clean edges if/when the plates get out of alignment. This 
involves either spreading or "choking" two adjacent colors into each 
other a bit so if something gets out of alignment, you don't see 
white or jagged edges showing through. You can't trap a raster image 
like a tiff. You can trap fonts and line art in a program like Quark 
or Illustrator. When the imagesetter generates the film, it includes 
the trapping info.

More reasons to have a pro - or at least a knowledgeable person to 
guide you along. And you need to know all of this BEFORE you start 
your design. For black text on white, like yours, Alex, it's probably 
OK to just go with a tiff. 100% black ink has no line screen 
issues... but if someone is working with elaborate design elements, 
colors, etc.... there are just a boatload of variables!

Now everyone should take all of these discussions and compile them 
and you'll have a pre-press 101 textbook!

AWG

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