Color management experience in EFI digital proofing
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Digital proofing has been developed along with the development of CTP direct plate making technology and is an indispensable part of digital workflow. Of course, digital proofing is not limited to the specific part of “printing proofs”. It is a specific application of the core technology of color management. It is based on color management and cannot be separated from color management technology. This article combines EFI digital proofing software to describe the color management process of the printer, which can match the proofing and printing.
First, what is digital proofing?
Generally speaking, the publisher or other customers only officially start printing the printed materials required by the customer after receiving the proofs provided by the printing company and signing the confirmation. In this process, the process of making a printed sample by a printing or proofing company based on a film or electronic document provided by a plate-making company is called proofing. The customer checks the layout design and print quality of the printed samples and signs that the sample can be used as a basis for printing. This process is called signing.
Digital proofing is based on the color range of the printed color and the same RIP data as the printed content. The digital proofing device is used to reproduce the printed color, and the proofing process can be made according to the actual printing condition of the user.
In theory, the color proofing device has a color gamut larger than the printing color gamut, and can be controlled by software to convert the color space between the output devices, so that the digital proofing effect simulates the color effect of the printing output device, that is, the color management process of the digital printer. Digital proofs replace traditional proofs.
At present, the digital proofing system consists of two parts: digital proofing output device and digital proofing control software. Among them, the digital proof output device refers to any color printer that can output digitally, such as a color inkjet printer, a laser printer, and the like. However, the printing speed, format, screening method and product quality that can meet the requirements of publishing and printing are mostly large-format color inkjet printers; digital proofing software is like EFI digital proofing software system, screen digital proofing system, Founder digital proofing system, etc. Wait.
Second, color management
Color management is a scientific and digital method that corrects various devices and records the color characteristics of the device in a “characteristic file” to obtain predictable colors on the device and reproduce colors in different output environments. under. This is achieved by establishing an objective set of rules for color communication between devices to ensure consistency in color delivery throughout the printing system.
It is precisely because the color management system provides the possibility of consistent color in the case of using different raw materials between different devices, digital proofing can replace the traditional mechanical proofing and become a new proofing method. Therefore, digital proofing is a specific application of the core technology of color management. It is based on color management and cannot be separated from color management technology.
There are three parts to the work involved in color management: device calibration, device characterization, and color conversion.
1 device calibration. It refers to the standardization of the color characteristics of the device, which produces a predictable color from a specific color input value. In order to compensate for changes in equipment aging or other factors, the equipment must be calibrated periodically.
2 device characterization. Each device should have its corresponding color characteristics. The color characteristics of the device can be recorded by a combination of software and hardware to generate a "feature file". Device characterization is the creation of an ICC Profile that describes the color characteristics of a device.
3 color conversion. When the same image is output on different output devices, different effects are produced because the gamut sizes of different devices are different. When we want to set the color of the A device and go to the B device to output, we need to use the “feature file” of the A device to perform color conversion and matching through the color management software to find the best color performance.
Third, color management in digital proofing
1. Device Calibration - Printer Linearization
The linearity of the ordinary color inkjet printer has a problem, and it is manifested that more than 90% of the dark color cannot distinguish the tone change and the parallel phenomenon occurs, and the linearity of each printing primary color is also different. If the feature file of the sample output device is created using the standard color table output by such a printer, an error occurs in the device characteristics reflected by the feature file of the output device. Therefore, printer linearization is the first step in implementing digital proofing color management.
In EFI, the printer linearization process is as follows:
1.1 Ensure that the Linearization workflow is smooth, that is, the arrow is displayed in green and the user, the Linearization workflow, and the printer are connected by black lines, as shown in Figure 1.
1.2Linearization process, parameter setting of Linearization device. The parameter settings of the linearization process are mainly the settings of the printer, such as the printer model, device name, connection port, print media quality, and so on. Click “Linearization device” in the process control panel. The property bar on the right side of the interface changes to the property bar of the output device, and the property settings are completed under the corresponding tab. The color manager function button is activated when the settings of the printer, etc. are completed.
Click the color manager function button, and jump out of the color manager interface window, as shown in Figure 2, click the "Basic Linearization" button to enter the printer linearization work window.
1.3 parameter settings, as shown in Figure 3.
Make the relevant settings in the window that appears. Select the measuring device, set the resolution, print mode, ink type, color mode, paper name (you can define the paper name yourself, easy to find later), dither mode, etc. When you are done, click Next and go to the next step. Note that the parameter settings here can override the settings in step 2.
1.4 The maximum ink volume is printed, as shown in Figure 4.
This step helps calculate the maximum ink value. The theoretical value is 400 and the empirical value is around 300. The chart is printed according to the maximum amount of ink of the theoretical value of 400. If the ink on the paper is found to accumulate, observe the color block where the black is the most saturated and there is no ink accumulation, and the value under the color block is 314 as the predetermined total ink limit. Print the color chart and cycle to the no-ink accumulation. After the ink on the paper is dry, click on the measurement until the measurement is completed.
Note that the software will automatically generate the total ink limit here, as shown in Figure 215, or you can change it manually.
Click "Next" to continue after completion.
1.5 the amount of ink per channel, as shown in Figure 5.
As above, the color table is printed and measured, and the software automatically calculates the amount of ink in each channel. The user can click on the "Advanced" button and manually adjust the amount of ink in each channel in the open panel, as shown in Figure 6. To accurately match the reference profile, click on the "Select" button to select the reference profile. As shown in Figure 6, the single-channel ink limit will be changed according to the print profile. If necessary, it can be manually adjusted by dragging the drag of each color channel, generally within the blue mark range. After confirming, exit and proceed to the next step.
1.6 Same as above, complete the printing and measurement of the basic linear table and quality control color table, as shown in Figure 7 and Figure 8.
Note that the quality control color chart is printed in two parts. The Gradient Patch section is used to visually observe the continuity of the color. If there is a jump phenomenon, you should return to the ink volume per channel to reprint the measurement. Print a measurement of the quality control color table, you can create a report, this report records some basic linear information, as shown in Figure 9.
Click the "Save and Finish" button to save the finished basic linear file (*.epl). Its default path is C:Program FilesEFIEFI Colorproof XF 3.0ClientWorking.
1.7 The basic linearization of the printer is completed.
Note: After replacing the consumables such as paper and ink or manually adjusting the printer, you must re-linearize.
2. Production of feature files
Printer characterization is a very important part of color management. The basic process is to use a standard color chart file such as IT8.7/3 or ECI2002 to print a digital proof sample of a standard color standard file through digital proofing software and a color printer. Tests and calculations were performed with a spectrophotometer and dedicated software to finally obtain a paper profile that reflected the characteristics of the color printer and print paper.
2.1 Click the “Create Print Media Profile” button in the Color Manager window to enter the “Create Profile” window, as shown in Figure 10. The relevant settings are made in this window, mainly the selection of the measuring device, the basic linearization and the selection of the printed color standard.
When the setup is complete, click Next.
Figure + Figure XI
2.2 measurement overview file chart
This process is completed in three steps, as shown in Figure 11. The first step is to print a sample of the standard color code file. After the sample is completely dried, complete the second step and measure it online. The third step is to create a profile (*.icc) of the print media. Its default save path is in C:Program FilesEFIEFI Colorproof XF 3.0ClientWorking.
Note that you can edit the black point generation by clicking the "Edit" button in the lower right corner of this dialog box. Generally, no changes are made.
2.3 After the panel display profile is created, click the “Finish” button in the panel to create the profile of the print media.
3. Color management settings in the workflow
After the printer linearization and the printer's characteristic file are created, in order to match the digital proof and the printed proof, it is necessary to set in the digital proofing workflow, so that the digital proofing effect simulates the color effect of the printed output device.
3.1 In the process control panel, click on the workflow you want to set, and the property bar on the right becomes the workflow property bar.
3.2Select the "Color" property. In the color properties bar, select the Color Management tab, and in the tab panel, check the Use color management checkbox. As shown in Figure 12.
The "source" will select the print profile, ie the CMYK at the "source" calls the print target ICC curve. "Coloring Intent" is selected as needed.
There are five options for Coloring Intent, which are absolute color conversion, relative color conversion, intuitive, intuitive-absolute and saturation. When one device space is mapped to another device space, if some of the colors on the image are outside the gamut of the target device, these four options represent four different color conversion schemes.
● Absolute colorimetric: The difference between the image obtained by the absolute chromaticity conversion and the target color is the smallest. Therefore, when converting, you should consider the white point of the target draft. For example, for a picture printed on newsprint, there is a significant difference between proofing and newsprint. In order to get the smallest color difference, paper white spots must be considered. This option is often used in digital proofing.
● Relative chroma: The nature of the relative chroma conversion is very similar to the absolute chroma conversion, except that the target color sample and the white point of the source color sample need to be matched, if the above image is printed for the newsprint, the It is a relative chromaticity conversion. The result of the conversion is very similar to the absolute chromaticity conversion, but there is no white point to simulate the newsprint and it is directly the white point of the proof paper.
●Saturation: When using a printer to output a picture or artwork, it is necessary to retain the maximum saturation as much as possible. It is not so important to be consistent with the original. This conversion is intended to be used minimally on a daily basis.
●Intuitive: The intuitive conversion intention is to take into account the paper, the gradation, the color characteristics, and the like, thereby obtaining an image that is perceptually closest to the original. This coloring intent is best for printing photo images, because it is more important to get as large a color space as possible than a color-accurate print. Therefore, it is not recommended to output color proofs.
● Intuitive - Absolute: This coloring intention was developed by EFI. It combines the advantages of the "intuitive" rendering intent with the color accuracy of the rendering intent "absolute color" and paper whiteness simulation in terms of image definition in the shaded area. This rendering intent is especially suitable for photographers who need to convert large source color spaces (RGB) to smaller target color spaces (CMYK).
Use the built-in source profile option. Check this box to enable object-oriented color management, where each image is automatically processed using the built-in profile in a print job consisting of different images. Any image without a built-in profile will be processed using the profile selected in EFI XF.
Simulation Profiles column. The simulation profile can simulate the output on a particular press. In general, the selection of this list file is consistent with the selection in "Source" or "None".
Note: If the reference profile is a profile created by the company itself, the profile should be placed in the fixed folder "EFI-EFI Colorproof XF 3.0-Server-Profiles-Reference" so that the profile created by itself will be displayed in the description. In the file list.
3.3 When the parameter settings are complete, click the Save tool in the main panel toolbar.
Fourth, the conclusion
Digital proofing has evolved with the development of CTP. The development of CTP has saved the process of film output, which has enabled digital proofing to have a new development platform. At the same time, the maturity of the color management system has made it possible to match digital samples with printed samples. Digital proofing has become an indispensable part of digital workflow. This paper combines the EFI digital proofing system to describe the color management part of the digital proofing system. It hopes to promote the technical transformation of the printing industry by promoting the application of digital proofing technology.