Digital Proofing Color Management (Part 2)

Ten, Photoshop's color management settings

How to accurately simulate the final color of the screen, in the Photoshop color settings will have a color gamut in use, that is, the work of the color space, the other side there will be a CMYK is the printing press ink, it is recommended if you can Using the ISO standard, the ISO Target is downloaded in the association of eci.org, and then the Target is placed in CMYK. It is recommended to use the reserved description file. The color gamut conversion uses relative colorimetry. As long as the printer's ICC Profile is entered, no matter which printer is on the screen, the colors printed by the printer can be seen.

Specifying the description file is not the same as the conversion description file. The specified description file refers to an ICC profile. The conversion description file requires two ICC profiles. If the RGB image file uses the specified description file, the CMYK can never be seen. Color description, only see the color description of RGB. If the RGB image taken by the digital camera is converted into a description file when the color gamut is converted, the two color modes of RGB or CMYK can be converted and displayed. Photoshop provides a view, which can be customized in the proofreading settings. In other words, when RGB has not yet been converted, it can predict what kind of results will be printed when printing.

Eleventh, the printing presses the stable quality science and technology

For printed matter, RIP before printing produces CIP3 or CIP4 format, CIP4.PPT formats ink coverage converts printer ink key coverage, and print data is full coverage, which must be converted to the printer used. The provided ink key ink control material, the stable printing technology includes the function of automatic upper and lower printing, cleaning, regulation, and pre-inking, and the scanning and feedback of the printing plate through the spectral densitometer allows each ink key to reach the previous The set density value can be used to monitor the progress of the printing process and the state of the printing machine.

XII. IPA Special Report (2004. Jun 8~10)

IPA has a total of 15 vendors and 31 sets of proofing systems for testing. The standard of our proofing system is to use GRACoL's CGATS-DTR004 Reference Characterization test guide. There are five test items: 1. Colorimetric Matching (Comparison of IT8. 7/3 Measurement to DTR004) 2. Visual Color Matching-Visual Match to GRACoL Press Sheet 3. Spot Color Measurement-Solid Spot Measurement Compared to Target Lab Values ​​4. Spot Color Visual-Visual evaluation to Pantone Spot Color Books 5. Altone Test Suite evaluations-Technical and Visual Page from the Altona Suite Were Evaluation for Conformance to PDF/X Standards Each guidebook will have an average error value. The average error value is the average of 1485 color patches using the ECI2002's guide. Can achieve 0.83, is very accurate, then its biggest error is 3.5, in 2004 the new color error average error specification is 2, I hope to be able to do 2 is a very accurate average error, the maximum color error should not exceed 5 If you look like this, only one company can achieve this level The other will not work, so the others are still in progress RIP space.

XIII. ICC Basics

ICC color management, there is another method is the CMM (Color Management Modules Microsoft), there is another is the CMM (Color Matching Method) plus a Color Engine (Adobe), there is a CMS (Color Management System) system Just like Apple's ColorSync or Kodak, this PCS Profile Connection (ICC Specifications) is the space for color conversion, or RCS Reference Color Space (Adobe).

ICC special input language, Input profile (color space to PCS), Output profile (PCS to color space) and Display, Device link, Color space, Abstract, Named color (ie Pantone, HKS), Color space mode It can be CMYK, Grayscale, RGB, Lab/XYZ. Device link is to say that two ICCs or three ICCs do the linking action. One is the Input printed matter, and Output is the digital type. These two ICCs can be linked together. The two are linked together by a CMS software. The Color Engine does the conversion, so today assumes that the RIP does not allow the colors to be used. You can use the Device link, which can be combined to three, that is to say there is a simulation object, such as the color of the Japanese input today, but the print It is to give the United States, so to get this manuscript to print standards like the United States, so it becomes three, Input is the Japanese color, the analog object is the SWOP, the output is the press, so this can be combined into three. There is a relatively good paper to play a better color gamut, so that the color gamut is reduced one by one, so that the level of this type of play is much better than the level of a large color gamut directly into a small color gamut, so the color gamut The conversion is certainly a technical issue.

ICC Basics is actually very good, but there seems to be room for improvement, because some data will be lost when the gamut is compressed. Is it possible to find a way to lose the least, that is Workflow does the color mapping table. The computational space of the ICC is actually a 3X3 matrix. From Gamma's RGB to White point to PCS's XYZ, can we do more matrices to make the colors more accurate? It also means that CMM will have different results in different profiles (RGB, CMYK, Grayscale, Lab). Another method is Workflow. Input Reference is the data of Lab. You can go to Proof when doing Contone. After that, do Measurement after Proof, then Compare after Measurement, then go to Proof, Proof. After finishing, go to Measurement, and then go to Compare, so this way of comparison, you can do a very precise color point of each color, so the error can really be less than 1, so it's like a Workflow Tbale The method, that is to say, has always been giving feedback. If you give back, you can make the color more precise.

That network proofing is actually the same principle, that is to say the input point, change the size of its outlets, is the measured Lab data, the relative Engine to convert, after the network size has changed, to meet the data of Lab, the same It's all about doing Match. Because the dots are expanded, they can also be simulated when playing at the dot. Generally speaking, dot dots must be simulated to play Dot Gain. Because Dot Gain simulates, the entire color will be accurate.

XIV. Application of color gamut conversion

Color gamut conversion involves color conversion between instruments and instruments or between instruments and materials or materials and materials, including printers, digital prototypes, designers, lithographic gravure and flexo, and the printing industry. The so-called printing press means that in different printing plants, it can be predicted or pre-processed, so that each printing house prints the same result. According to the mechanism just in the past, it means that the printing press prints a guide and then puts itself The standards, for example, say that we use ISO to convert the ISO standard into the color gamut of printing presses, so that the printing press can print ISO standards. Therefore, when implementing the standardization, the problem is not in the printing factory. The key point of the printing factory is only to stabilize the manuscript. However, if the standard color is to be played, the key point will be before the printing. If there are four plates, it will be given today. The same data is printed for different printing factories. Different printing companies will print different colors. If you want different printing companies to print the same color, you need to give different data, so after a conversion like this, Let the two printers print the same color.

There may be different printers in Misbishi, Komori, and Heidelberg in the printing plant. There is no difference in using this mechanism to make different printing presses. It is only necessary to let the printing press print color guides and know the color space of the machine before printing. When the film is published, when it is published, the color gamut is converted into the desired color in advance so that the three printing machines can print the same color. This is the use on the printing press. In terms of file format, the gamut conversion is almost all converted in Photoshop, so it can only change the pattern. Is there a mechanism to transfer PDF and Postscript, because the last large version is all PDF or Postscript files, so it should be found One can do the color gamut conversion, but the gamut conversion must be done accurately. Just talking about ICC is impossible, because the ICC has the problem of gamut compression, the only way is to do a color correspondence table, color correspondence table it Each patch is accurate, and any two printing houses can print the same results as long as they are stable enough. If the digital sample is to be proofread with the printed matter, it is actually very simple. After the digital printed paper and ICC have been completed, it will be done for the second time, that is, to re-align the digitized sample. Table, measuring the second ICC, is to turn ISO into the second ICC calibrated in the second color, and then take this ICC image file for digital proofing, which will be very precise; in fact, there is no need to adjust RIP curve, as long as the alignment of the ICC and then make a second ICC, then I do the conversion in Photoshop, so that you can be very accurate, you can not need to adjust the curve, so Such a mechanism is very simple.

Designers, why designers, because different advertising companies may adopt different standards in the conversion of color gamut, for example, Japanese manuscript standards are adopted, but printers usually receive several advertising companies. The manuscripts, but each company's advertising company adopted different standards, this time is to do color gamut conversion; from the color domain of different advertising companies directly to the color gamut of the printing plant, so the printing plant can play customer The desired color. As long as the pre-gamut conversion is converted into the color that the customer wants, it will be converted into the standard in the printing factory; so it is very simple. If the customer adopts the ISO standard, he will turn the ISO into the standard of the printing press in the factory. The color of the ISO standard is printed, so when the designer receives the manuscript, he can do the conversion of the color gamut in advance.

Then there is the lithographic, gravure, and flexo. How to convert Flexo's colors to lithographic printing is the same as doing color gamut conversion. First measure the color gamut printed by Flexo and turn it into a lithographic printing machine. The domain, as long as the color gamut is converted, the printed color will be the same as the Flexo India color. If it is gravure, it can also be used to change the color gamut, and the customer can get the desired color. .

The final step is the printing industry. If you give an RGB electronic guide to a print shop, you will rush out and put the RBG's color gamut into it. Then you make an ICC Profile, and then through Photoshop's gamut conversion. After the conversion, it will become An image file is flushed to the print shop. The RGB color guide on the printout will change very well, and the color will become very accurate. It will be the same as the color that was originally seen on the screen. When the color is not controlled, it needs to be converted in advance. If the color can be controlled, the conversion will be done at the time of printing. Therefore, there are two ways to change the color gamut. The conversion of the color gamut only has two key points. Specify the description file and the gamut conversion. Specify an ICC profile. The color gamut conversion is two ICC Profiles. So, what color is the color rushed out of the printing shop? Specify the color profile Adobe first. Or RGB, so the color seen on the screen is the standard of sRGB, and the color printed on the printing machine of the printing shop will also have an ICC Profile, so it can be converted in advance and it can be changed from sRGB to Kodak. The colors that are punched out by the printers of Agfa or Konica, as long as they do the color gamut conversion, the colors printed out are actually the same as the colors seen on the screen, so this kind of conversion is a pre-transformation. Normally, printers will decide the color gamut to be printed when they are to be printed. For example, if CMYK prints are converted to RGB ordinary printers, then these two gamuts will be converted if the computer is not directly Connected to the punching machine, then put the file