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Adobe Acrobat 9: Grayscale PDF = A Smaller PDF

by David R. Mankin

PDF files come in all sorts of color profile flavors:

  • CMYK (cyan-yellow-magenta-black) colors used in the traditional 4-color offset press process
  • RGB (red-green-blue) colors used in video screen rendering
  • Grayscale (varying shades of black-gray-white)
  • Monochrome (line art)

It is logical that these file types would “weigh” differently.  Images with millions of colors will contain considerably more information than an image comprised of 256 colors.  Glorious, colorful PDF files look wonderful on your screen, and will certainly reproduce vividly on a color inkjet or laser printer.  Is this color important though?  If you’ve designed a flyer or newsletter and are distributing the document in PDF format, the color is likely a critical aspect of the document.  If, however, your PDF file is part of a workflow in a law office, the color may be incidental, and may actually add nothing to the document’s purpose other than bloating the document’s file size.

Print shops manipulate PDF files all the time to adjust your work to their equipment & processes.  If you send out a PDF file for offset printing, and you accidentally used an RGB image in your work, it can be converted to the appropriate CMYK color system by using Acrobat’s Preflight feature.

Preflighting is the process of confirming that digital files are correctly formatted for the desired output method.  Acrobat’s preflighting tools have matured vastly in recent Acrobat releases, and not only perform checks, but repairs & conversions.  As an example, I have a full color PDF file (CMYK).  The file is 3.23 Megabytes.  Since my colleague does not have a color printer, I could opt to send him a version of this document that I have converted to grayscale in order to save on precious file space.

To convert a PDF file to grayscale, click onAdvanced>Preflight… Click the triangle to the left of PDF fixups.  Here you will find a wide variety of conversions and fixups.  Find the Convert to grayscale & double click.  Acrobat takes you right to a Save As dialog box, which will allow you to rename the file, preserving the original.  In this example, the newly-created grayscale document is only 1.73 Megabytes.

Don’t think that losing all those colors is always a terrible thing – try watching Casablanca colorized some time.  Yuck.
Adobe Acrobat 9: Grayscale Images

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