Successful color management in PDF workflows (5-3)

PDF file generation

PDF files generated using desktop applications can result in a file with many uncertainties. Although all files conform to the specifications of the PDF language, the marking or color conversion process may require different steps. Regardless, our goal is to generate a device-independent digital management file.

In general, there are two ways to generate a PDF file from an application: either the Save As or Export commands can directly encode a PDF file. It is also possible to first print the file output as a Postscript file (some specific software) and then pass the file to Acrobat Distiller to generate a PDF file.

Adobe Photoshop 6. Photoshop 6 inherits Photoshop 5's concept of storing colors in the "workspace" and further extends it so that each image window in the Photoshop application can contain colors in different workspaces. Combining images from different color spaces together, the colors can be converted using the ICC profile.

PDF is one of the optional formats for the Photoshop Save As dialog box. There are two related options when defining colors in a PDF. One is the "Embed Profile", which generates a PDF file that is defined as an ICCbased color. The profile associated with this definition is also the profile of the workspace in which the definition file is stored. This storage space may or may not be the current workspace. If the Embed Profile option in the PDF file is not selected, the colors in the file must be device-dependent (DeviceCMYK or DeviceRGB).

The second option is "Use Proof Setup", which converts the colors in the file to the currently selected Proof Setup color definition and then uses ICCbased to encode the PDF color.

Adobe Illustrator 10. Illustrator 10 also uses the concept of workspaces in Photoshop 5 and 6. Unlike earlier Illustrator versions, Illustrator 9 and 10 files must be completely in one workspace; this means that it is not possible to have both RGB and CMYK defined colors in an Illustrator file, which makes it easy for many service providers.

Like Photoshop, Illustrator also uses the Save As command to generate PDF files. And Illustrator also provides an options dialog, which includes "Embed ICC profile" option.

If the embedding option is set, Illustrator will use ICCbased coded colors, using the profile of the current workspace (RGB or CMYK). If ICC profiles are embedded in the placed images, they are automatically converted to the current workspace. Therefore, device-independent PDF files generated by Illustrator tend to have only one ICCbased color definition, although it may relate to a lot of page file objects.

If you do not select an embedded project in Illustrator 10, the stored PDF file will vary depending on the file's color space, such as DeivceCMKY or DeviceRGB colors.

Adobe InDesign 1.5. InDesign software allows each object in the file to have a separately set ICC profile. The InDesign file also defines the color in the file through the profile, and each of RGB and CMYK.

Using InDesign to generate PDF files can be achieved through the Export command. PDF Export Style can be set to control multiple options at the same time. If the "Include ICC Profiles" option is set, InDesign encodes each page object based on ICCbased and uses the InDesign document Color Management settings to specify the assignment of the profile.

The process of importing (dropping) an object is determined by whether or not the object embeds an ICC profile. If embedded, these objects are defined as ICCbased colors, and their properties file appears in the output (including the imported PDF file). If there is no embedding, you can specify one by using the Image Color Setting command in InDesign, which will be based on the ICCbased definition in the PDF file (but the Image Color Setting command cannot specify a PDF file). In addition, these objects will also be coded as DeviceRGB and DeviceCMYK colors.

Quark Xpress. Xpress 4.1 does not generate the PDF file itself, but is created by a PDF filter provided by Quark (currently version 1.6, which can be downloaded from the Internet). The filter adds the Export PDF command to the Utility menu of the Xpress software. The PDF Filter requires Distiller to be installed on the user's machine, and Distiller PPD is selected in the Quark software's Export PDF Options list. The filter writes a Postscript file to the disk, runs Distiller, and deletes the file after Distiller is finished.

The characteristics of the final PDF file depend on Distiller's current Job Options. If configured Distiller can generate PDF files of version 1.3 or 1.4, and if you have configured the appropriate color settings, you can obtain a device-independent PDF file and use the ICCbased color space to record colors. This file will convert all RGB colors to CMYK using the properties file selected in the Xpress software Color Management Preferences command before Postscript is generated. However, since Xpress 4 does not support the import of PDF files, vector objects cannot be color managed.

If there are some import objects embedded in the ICC profiles and some are not, you will encounter a trap. Objects without embedded profiles may use exactly the same color space as the CMYK profile selected in the current Xpress, so they are not converted and will still be marked as ICCbased in Distiller. Objects with profiles will be converted to the current CMYK color space and then labeled as ICCbased in Distiller. Only when Distiller uses the same color space as ICCbased and is used to combine print files in Xpress can this scenario be successful - that is, all the colors in the file have already generated a profile before Postscript.

Ideally, a uniform workflow should be set up in terms of color definitions, Xpress settings, or Distiller settings. (Homogeneous workflows are where all objects are either tagged or untagged, not a mixture of the two.) If you have to deal with a mixed object page (with or without an embedded profile) ), a desirable defense is to use Photoshop to convert them all to the same color space before importing these objects.

Macromedia Freehand. Freehand 10 provides Export PDF instructions just like any other application. However, this Export feature produces a PDF 1.1 (equivalent to Acrobat 2.0) file and cannot be processed further; ICC based color space requires a PDF file of 1.3 (equivalent to Acrobat 4.0) or higher.

PDF files can be placed in FreeHand documents and can be color managed with ColorSync. However, taking into account the export of PDF files, if the format of various objects are correctly converted to the template printer profile, it is beyond the scope of this article. In fact, the best way to generate this is to save the colors that share the same device-defined definition as the format of an EFS or Postscript file. The .eps or .ps files are then tagged with these color objects in an appropriate profile and processed by Distiller (see the Distiller section below for details).

Microsoft Office applications. Excel, PowerPoint, and Word cannot output PDF files directly. Different color collection tools can be used to define colors in these applications, including direct access to CMYK percentages and RGB percentages. (This method is the same as Xpress, but it is different from the 8-bit value used in common image editing software.)

Generating a PDF file from an Office document requires using a system print driver to generate a Postscript file, which is then processed by Distiller. Postscript files generated from Office application documents use DeviceRGB to record all colors, so it is best to use RGB to define colors in Office documents; in this way, appropriate property files can be arranged in Distiller. Using CMYK to generate tones in Office applications translates to RGB values, making it impossible to clearly understand the correct profile.