In the process of proofreading the customer's electronic documents and guest color drafts, if the color of the digital draft or soft proofing effect output by the customer's electronic files in accordance with our printing standards is different from the color of the customer's follow-up digital draft, And the color difference direction is the same, you can batch process color conversion.
From the principle of color management, color = profile (electronic file), which is equivalent to y = f (x), where the final color of different color characteristic files for the color description of the same electronic document is different. Therefore, this color difference is mainly due to the fact that the simulated color characteristics of the digital output of the customer are not the color characteristics documents of the printing plant that is requested to be produced. The digital manuscript or soft proofing effect of the same electronic file output according to the factory's printing color characteristics will generally be different from the customer's digital color. Check the color effect produced by the factory's printing and the customer's digital color Analyze color differences. If the overall tone of the individual colors is consistent, the electronic document can be color converted in the process.
The first case of color conversion, RGB to CMYK, for the mixed PDF format of guest PDF files, the RGB images and color blocks should be color converted in the process. The current main market process is smooth, Kodak Prinergy and Wichi of the screen can all realize the RGB to CMYK color conversion, which is also a requirement of the process software to realize the prepress RGB process. For the process of achieving color conversion in the process, it can have a reliable effect, and the color output of the converted file must be proofread by color output. According to the requirements of color conversion, the CMYK color space is output, and the color characteristic file of the printing factory should be placed, but the color test is performed on the description file of the RGB color space, and the best description color file with the converted color is selected. Some pre-press production staff may think that the color space of RGB Adobe1998 is large, and the same electronic file, using the color described by it is the best effect, which is actually a misunderstanding. Many electronic manuscripts are taken by digital cameras, but the RGB color characteristic files of digital cameras are generally the default sRGB. Therefore, in many cases, the sRGB color characteristic file is the closest description file for color conversion.
When different printing standards or different printing houses print the same book, the printing effect is often different. This is mainly due to the difference in printing factory environment and conditions leading to the difference in printing standards. Therefore, when it is detected that the color of the customer's color draft is different from the digital proof or soft proof proofed by our factory, the evaluation of the color difference must be accurate. If this difference cannot be made up during printing, or the adjustment of the printing cannot be done When the customer is satisfied with the printing color, this also requires color conversion of the customer's electronic manuscript before printing to make up for the difference in printing standards. The color conversion model can be expressed as CMYK1 to CMYK2.
Among them, CMYK2 is the color characteristic file printed by our factory. The use conditions of these color conversions are that customers have higher requirements for printing and color. The color differences of electronic documents output from customers according to our factory's printing colors are consistent. Printing cannot be adjusted to compensate, and the number of files is large.
There are generally two methods for applying color conversion for color correction: one is to obtain the color characteristic file printed by the customer's digital manuscript, which requires the customer to print a color target image while the digital manuscript is being provided. Or with the printing color characteristic file simulated by the customer's digital draft, if it is a color target with printing conditions of the customer, the color target data measured with the measurement software is used to generate a standard ICC color characteristic file, which is considered to be the output color characteristic file of the customer's digital proof . Use it to describe customer files, and the color characteristics of the customer's digital manuscript will be restored to the printed color characteristics of the factory. Another method is to edit the specific color characteristic file to make its color characteristic compensate for the color characteristic of the printing plant's color characteristic file, use it to describe the customer's electronic file, and then convert it to the printing color characteristic file. These two methods can effectively and quickly correct customer electronic documents when the color cast of the customer's digital manuscript is serious. However, the electronic files after color conversion have been re-separated, which requires that the color separation parameters of the printed color characteristic file and the description of the printed color characteristics of the Qi team's factory must be quite accurate and reliable. In addition, it is a color conversion file. The retention of grayscale images and the retention of black characters must be rigorously tested. It is possible to ensure that all aspects of color patches, images, grayscale images, single black characters, etc. before and after color conversion are available. Very good color matching.
Make color conversion in the workstation, whether it is RGB to CMYK, or CMYK1 to CMYK2, after conversion, the color and file type of the digital output of the file output according to the factory's color standard must be strictly checked. Prevent differences in image content and differences in printing effects due to color conversion.
Color conversion in the process is an important way to make up for different printing standards that cause the same electronic file to output differently in different printing plants. It is also an important idea for open color management of the entire process. It is an important link and means for color management to realize color proofing of electronic documents before printing. Therefore, it is still very helpful when dealing with foreign orders that are different for many digital proofing standards.
Attached:
Retain the ICC Profile layout and the process of color conversion test in the process. Test purpose:
Examine the effect of retaining the ICC profile file in the development software and loading the Icc profile in the process. Prove that using the appropriate ICC Profile in the process can effectively carry out the expected color conversion and achieve the effect of the most faithful manuscript in the color reproduction process.
testing method:
1. CMYK security mode issuance, loading color configuration files in the process
2. Retain the layout of the image color configuration file, and do not ignore the color configuration file in the process
Process one:
1. Make a standard PDF file, as shown in J2001.tiff
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In Indesign software:
a. Color setting: Simulate Adobe Indesign2.0 color management system is closed;
b. Print PS file: choose the color determined by Indesign;
c. Convert to PDF file in Distiller;
2. Check the PDF file in Acrobat software, no ICC Profile
3. Add JanpanType1.icc in Prinergy
Process two:
a. Check the image color configuration file JanpanType1.icc in photoshop software
b. Indesign retains the image ICC profile color configuration file layout:
In Indesign software:
i. Color settings: keep color configuration files;
ii. Check the image color configuration file
iii. Print PS file: choose the color determined by Postscript;
iv. Convert to PDF file in Distiller;
d. Convert to PDF file in Distiller;
e. Check the PDF file in Acrobat software, there is ICC Profile JanpanType1.icc
f. ICC profile is not ignored in Prinergy
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Compare PDF files output in two ways
Comparing results:
The CMYK value of each color block is the same. As shown in the figure, the bottom row of the original image C100M100Y100 becomes C82.0M51.4Y25.7K44.7 after being output in different ways.
Principle of analysis
Through this test, it can be concluded that the use of ICC Profile for color conversion in the process and the preservation of the image color configuration file in the process can maintain the original color characteristics of the image and the effect is consistent.
Therefore, for an image with a color profile, in the actual production process, there is an electronic file with an ICC color profile, and the digital proofing is closer to the color containing the ICC Profile. You can process the image color in the above two ways to perform color Only the conversion can guarantee the realistic reproduction of the image color.
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