Understanding Adobe Photoshop: Digital Imaging Concepts and Techniques

The Portable Document Format (PDF) is a file format that Adobe invented. PDF was unveiled in 1992 and was intended to be an extension of PostScript. A PDF can describe any combination of text, images, multimedia, and layout. It is independent of the device it was created on, and can be viewed on virtually every operating system.

The PDF is an open-standard, which means that the computer industry is able to create applications that can read or write PDFs without paying Adobe additional fees. This openness led to the quick adoption of PDF, and it is utilized online extensively.

The most powerful PDF authoring tool is Acrobat from Adobe. This software is bundled with Photoshop in the Adobe Creative Suite Premium package. However, Photoshop (and most Adobe programs) have the ability to create PDFs. The PDF file format is an excellent way to send files to a service bureau or print shop as the file can be stored at print resolution with embedded vector files and high-quality output options.

Compression Options for Adobe PDF

When you choose to save artwork as a Photoshop PDF, you are presented with the Save Adobe PDF dialog box. You can choose to compress text and line art as well as downsample bitmap images. Depending on the chosen settings, you can significantly reduce the size of a PDF file with little or no loss of detail.

In the Save Adobe PDF dialog box, you can choose an Adobe PDF preset. This is a fast way to specify what is meant for commercial printing, distributed via email, and so on. You can click Save PDF to generate the file right away, or keep modifying the settings for special purposes.

Adobe PDF Standards

You can choose to create a PDF that matches the most widely used standards for print publishing. There are two different types of PDF/X formats:

PDF/X-1a (2001 and 2003)

PDF/X-1a is an industry-recognized standard for graphic exchange. Choosing PDF/X-1a requires all fonts to be embedded and for the appropriate PDF bounding boxes to be specified. PDF/X-compliant files must contain necessary information describing the condition for which they were prepared to be printed. PDF/X-1a compliant files can be opened in Acrobat 4.0 and Acrobat Reader 4.0 and later.

PDF/X-3 (2002 and 2003)

The main difference in this newer version of PDF is that it allows for the use of color management. Additionally, it supports device-independent color as well as CMYK and spot colors. Additionally, ICC color profiles can be used to specify color data later on in the workflow. PDF/X-3 compliant files can be opened in Acrobat 4.0 and Acrobat Reader 4.0 and later.

For more information on PDF/X, see www.adobe.com/products/creativesuite/pdfs/pdfx_white_paper.pdf

Compression

The Compression area of the Save Adobe PDF dialog box offers several options for reducing file size. You do not need to downsample, but you might want to if you want to better match the output resolution of a particular printer or to reduce file transfer times.

The chosen interpolation method determines how pixels are deleted:

  • Average Downsampling: This method averages the pixels in a sample area and replaces the entire area with the average pixel color.

  • Subsampling: This method chooses a pixel in the center of a sample area and replaces the entire area with that color.

  • Bicubic Downsampling: This method uses a weighted average to determine pixel color. It generally yields better results than Average Downsampling. This is the slowest, but most accurate, method.

  • Compression: Three methods of compression are available to use:

    • ZIP compression: This works well for images with large areas of single colors or repeating patterns.

    • JPEG compression: This is suitable for grayscale or color images. JPEG compression eliminates data, so it usually results in much smaller file sizes than ZIP compression.

    • JPEG2000: This is the new international standard for image data compression. Like JPEG compression, JPEG2000 compression is suitable for grayscale or color images. It also provides additional advantages, such as progressive display.

  • The Image Quality setting determines how much compression is applied. The settings will vary based on the compression method chosen, but they are clearly labeled.

  • You can check the convert 16 Bit/Channel Image To 8 Bit/Channel if you're working with a 16-bit image. This can significantly reduce file size, but is not a good option if you're creating a PDF for professional printing. This option is grayed out if the image you are working with is already in 8-bit mode.

Output

The most common way to create accurate color when creating a PDF is to stick with the PDF/X standard. However, you can choose to modify settings in this area and embed color profiles. Be sure to check with your printer or service bureau regarding color profile settings.

Security

The PDF format supports several different security options. This can be useful to protect the document from unauthorized viewers or to preserve copyright by blocking copying or printing functions. Here are some of the most important security options:

  • Require a password to open the document: The viewer must enter a password to view the PDF document.

  • Use a password to restrict printing, editing, and other tasks: Several options can be placed on the document. You can restrict printing and block modifications to the page.

Summary

The Summary area provides a single pane view of all of the settings you have used. This is a quick way to check the options you've enabled.

When you're finished, you can click Save PDF to create the PDF file. You can also click Save Preset if you want to save the settings you've modified for future PDF creation.

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