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PDF - Preparing Files for Print |
PDF (Portable Document Format) is a technology that was created by
Adobe Systems, first developed to exchange digital documents for use on
screen. It has gradually been evolved to be the printing industry's
standard.
PDF file format can be used for different purposes,
e.g. as individual ads, part of a job, a complete job, a digital proof
etc. It can include all the elements of the page, text, pictures and
fonts.
The PDF files can be of various quality, from high
quality made for printing to low quality with lowres images and useless
for printing. For example a PDF that was made to be a digital proof can
be useless as a final output for print.
Main benefits of PDF files:
- It is platform independent, it can be used on all popular operating systems.
- If correctly made, pictures and fonts are built into the file.
- No undesired textflow can take place.
- All PostScript errors which can emerge, will show up when the PDF file is made but not when job is output on plate.
- The files are smaller than PostScript files, more compact and do not include any needless data.
- All pages are independent, which means it is safer to work with multi page documents.
- It can be used as a soft proof.
- It is possible to lock the PDF files, so password is needed to open or print.
Main drawbacks of PDF files:
- Corrections can be troublesome, especially text corrections.
- One has to own Adobe Acrobat to make a high quality PDF.
Guidelines for PDF generation
To
make a high quality PDF file for printing, in most cases it is
mandatory to make a PostScript file first and run it through Acrobat
Distiller with the right settings.
Indesign PDF Export settings - Standard
Indesign PDF Export settings - Advanced
- w. no Down Sample and lossless compression of images
recommended for scanned linework/text in 8 or 24 bit mode images with highres pattern.
It is important that pictures and background that reach the edge of a page, bleed a minimum 3 mm out of the page.
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Resolution, color and grayscale pictures should not be lower than 300dpi, and black and white line art at 1200dpi.
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Do not scale above 20% if high quality is expected.
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In most cases EPS DCS (5 file format) do not work because PDF files should always be composit.
When pages are printed from the original application, make sure:
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Printing area is bigger than the final page size
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That they have bleed,
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Crop marks
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Sit in the center of the printing area.
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Do not print the pages in spreads.
Note:
Do
not use PDF Writer or similar shortcuts like "Save as PDF" unless you
are certain that the application supports real PostScript. PDF Writer
is not a true PostScript device and does therefore not handle all
picture formats or fonts correctly.
Preparing files for print
There are couple of things that designers have to bear in mind though
and are vital for the RGB Workflow
1. Profiles may not be removed from RGB images, but what profile is used
is not that important, it depends on were the image is from, keeping
the original profile from the digital camera is recommended, the profile
which is mostly used by professional photographer is AdobeRGB1998, sRGB
and ProPhoto are also popular. ProPhoto have the biggest color spectrum
and sRGB one of the smallest. But all the colorspaces are bigger than
the standard CMYK colorspace.
2. PDF files must be Exported from the DTP application and made with the
correct PDF export settings.
N.b. The PDF files may not be created with Acrobat Distiller, that is a
obsolete workflow.
Monitor Calibration
(Not vital, but to achieve the better match on screen)
ColorSettings have to be correctly set in Indesign, Photoshop, Acrobat
etc. Correct CMYK Profile needs to be selected to be able to Proof on
screen. N.b. it is not used to convert the images but only to look
through in the applications.
Monitors have to be at certain quality and have to be calibrated.
Working area needs to be with lit with neutral light and no daylight can
interfere.
More regarding RGB workflow - Why RGB workflow?
Until recently the normal workflow in offset printing required Image
data to be converted from RGB to CMYK colorspace early in the process.
Many print shops did even put a demand on their customers to deliver
digital files with only with CMYK data.
This is now a thing of the past in all High Quality Commercial printing,
since Adobe has solved their lack of support for the RGB workflow.
Before DTP applications could not embed RGB profiles in exported PDF
files and the raster image processors (RIP) could not handle RGB to CMYK
conversion correctly.
Now most of commercial printers prefer RGB image data to obtain the
highest quality. Doing the conversion from RGB to CMYK in the last
stages of the platemaking process maximizes the quality.
And last but not least, working only with RGB images simplifies the
workflow for the customer.
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