PDF and color management

The author teaches prepress technology courses such as output file inspection and color management. Frequently, students ask questions about PDF. Some people in the market talked about the benefits of PDF. Each prepress equipment company also made great efforts to develop the PDF process. What is the function of PDF and how does it work? This time, the author and everyone to study how PDF files with color management, so that the color is more accurate.

The full PDF name is Portable Document Format, and Chinese is a portable file format. A PDF is a database that converts a previously output Postscript code into a page. It can convert font, image, and vector objects in the original file into a file format suitable for a variety of purposes. In other words, the same file can be applied to different output methods, such as digital proofing, imposition, output film, CTP, digital printing, online transmission, browsing, and e-books.

After ten years of development, PDF has gone through five stages, from the PDF version of PDF92 in 2002 to the version of PDF1.4 in today, and more advanced versions such as PDF/X, etc. The following table shows the different versions supporting color capabilities. Comparison. Since ICD color management is only supported in PDF 1.3 and PDF 1.4 versions, the issue of color processing in Acrobat 5.0 is discussed here.

We need to use color management in PDF files. We must start with how to generate or convert PDF files. There are many ways to generate PDF, including (1) simple tools using PDF Writer, and (2) different applications such as Produced directly by PhotoShop, PagerMaker, FreeHand, Office, etc. (3) Produce the original document in the printing process, (4) Export the document into Postscript, then use Acrobat Distiller to produce, (5) Use some specialized software such as PDF Creator to Produce, (6) Use high-level output RIP to generate. The first method described above does not support color management. The second and third methods are limited to support color management. However, the fourth to sixth methods are relatively sophisticated and effective solutions.

Color settings in Acrobat Distiller

(1) Select Job Options from the menu Setting.

(2) Select the PDF version you need, if there is no special reason to choose the latest PDF1.4 version.

(3) Different color management modes can be selected in the setting of the Color option. If you want to set your own color management mode, you should select None.

(4) There are four kinds of options in the Color Management Policies. Leave Color Unchanged is to keep all the values ​​unchanged when converting PDF files. If you know that the next operation has already set the color management mode, you can use this option; Tag Everything for Color Mgmt (no conversion) is to keep all values ​​unchanged, but the selected ICC profile in Working Spaces is embedded in the PDF file as needed, so that the staff in the next process can know the ICC Profile of the file source; Tag Only Images For Color Mgmt (no conversion) has the same function as the previous option, but it does not affect the image of the bitmap. Text and frame graphics have no effect. For example, the image in the page is in RGB mode, and the text and frame in the frame are CMYK. , or if you want to change the color of the text part, you can use this option; Convert All Colors to sRGB This option is available if the PDF file is to be used for web pages or general display purposes. The PDF file converted from this option is finer. Easy to send.

(5) Optional Default in the Intent option, so that the color space conversion will be decided by the output part.

How to check the ICC Profile contained in the PDF file

Method (1): Select the image in the page with the solid arrow tool, and then press the Command and Option keys to double-click. This will start PhotoShop to open the image directly. You can see the embedded ICC Profile under this window. .

Method (2): Requires additional Plug-in software such as Enfocus PitStop. Use the white arrow tool to select the image in the page. The embedded ICC Profile is visible in the Enfocus PitStop Inspector window.

How to use the ICC Profile contained in the PDF file as a screen soft proofing

Screen soft proofing: Select Proof Setup->Custom from the Acrobat menu View, select the appropriate ICC profile, and then launch Proof Colors under this menu so that you can see the exact preview color.

How to use the ICC profile contained in the PDF file for digital output

Output digital artwork: (1) Select Print from Acrobat's menu File, followed by General's options for Acrobat 5.0.

(2) Select Advanced in the Acrobat 5.0 menu and follow the window below.

(3) In this use Print ICC Colors as Device colors and Apply Working Color Spaces, under the Color Profile select the printer ICC Profile digital writing, followed by OK to return to the previous window, press the Print key to print.

(4) After the completion, the left side is the original file, with the printed ICC Profile; the right side is the printed data, and is displayed with the printer's ICC Profile. The color of the result is basically the same as that of the left side. It is the result of using color management methods.