Seminar on
Evaluation of Spot Color Reproduction in Digital Process
By
Ms. Gauri Raju Adhalrao
Under the Guidance of
Prof. Dr. Akshay V. Joshi
Pune Vidyarthi Griha’s College of Engineering and Technology,Pune
Academic Year 2020-21
Printing industry is increasingly adopting digital technologies to complement or replace analogy ones. In last few years there is a quite fast move from conventional to digital proofing systems because of the introduction of computer to plate (CTP) systems. As CTP systems do not use film anymore in the plate making process so digital color separations is use to make proofs.As the proofing workflow is moving from the traditional proofs based on films to a complete digital printing approach. Although, digital color separations is already in use in the graphic arts market for some time, their use in proofing is not widely accepted until recently. A proof is used as the main quality check in print runs , color accuracy,color consistency and quality of a digital proofing workflow is to be as good. In today’s print environment where it is able to calibrate color output between offset and digital presses to achieve consistent print results, maximize productivity and manufacturing flexibility is absolutely essential. Digital printing machine proofing in the Western printing industry is become the mainstream mode of production. [1] The primary goal of proofing is a tool for customer to check that the entire job is accurate. The digital proof is also called as color proof which provides the color-reliable and true color reproduction of the contents of the file intended for printing. The quality of Digital proofing is improving continuously due to revolution of digital proofing device and color measuring device. To maintain color consistency and appropriate color matching digital proofing and printing is needed. [2]
Digital Proofing
The purpose of digital proofing is to provide standard stimulated reference for printing as the main purpose of a proofing system is to simulate a given printing process so that the quality of the proofing device can be directly determined by measuring its ability to reproduce the standards of printing process. The digital proof is of centrally important for digital imaging printing systems the separations of an image to be reproduced are exchanged digitally. While using digital systems for proofing the proofer needs to be color calibrated to maintain color accuracy and color bars should be used on every proof. Digital proofing system composed of high precision inkjet color printer or laser color printer through the color printing and simulation printing proofing color with tthe original data to check proofs. [3]
Fig.1: Digital Proofing
Image copyright © 2021 Agfa-Gevaert Group. All rights reserved.
Digital Printing
Collecting reference values by performing test printings are really the same as using the stored values in the profile, since they too are measured from a printed sheet once(fig.2). The main advantage of printing a printing is that the data will be more up to date. There will be no difference but since the printing process is affected by such a large number of factors. Making actual test printings also gives a possibility to collect data that is specific to certain conditions. To achieve accurate color matching in the job printing helps to find out difference between the printed work and the digital work to see whether the color has printed exactly the same way. The measurements can then be used to verify the colour proofs of the edition. For digital printing the proof printers are used and then the proofs are measured and compared in terms of press proofs and color accuracy and others parameters are checked. [4]
Fig.2: Digital Printing
©Image copyright © 2021 Abbott Communications Group
The quality analysis and control method for color management of EPSON 7600 color printer is done by following step. First step is equipment calibration and linearization and second step is to characterize the printer and get the profiles. Then after this the final step is the profile of printer and press should be embedded in the digital proofing to complete the color conversion and for obtaining accurate digital proofs a practical solution is that were the profiles of printer is edited and optimized properly after this the transfer of ICC profiles in color management process is printed the test charts. Again to compare the outputs of the printer color management before and after .We should established the evaluation model of color management and profile in which it should include the subjective and objective evaluations. From this it is illustrated that the quality analysis of printed matter requires a comprehensive analysis of combining subjective and objective evaluation. For subjective evaluation a compare the digital proofs and traditional print proofs by gray balance and test charts where it is found that the digital proofs have bright color, high saturation and excellent reduction of tone and Color reproduction of digital proofing is good and objective evaluation included the contrast of solid density, dot gain, gray balance, color difference and color gamut and then measure and compare it with offset printing. Through subjective and objective evaluation it seems that digital proof can match the national standard of offset through the editing and optimizing of profiles in standardized color management process. [5]
The accurate color matching can be achieved for spot colors by digital proofing in commercial prepress system by illustrating the problems and reasons while outputting the spot colors. For that firstly select 18 basic color codes for maps in that some are spot colors and some are process color then open this patches in Photoshop and set their L*A*B values and then transfer it to CMYK color mode using default color setting and save in tiff file. The colorimetric values of the original is transformed in the custom color settings and the almost the same result is found in which the average color difference is very less and another reasons is that the only device settings of output plan template in the software is needed rest parameters are kept as default settings and several proofing correction are accurate in matching. [6]
The reproduction error in a different color gamut based on digital image color through different color gamut mapping method image processing software can be done by obtaining the corresponding image effect in which 4 gamut mapping ways is selected in Photoshop respectively corresponding to the color space conversion and then print the output. So for handling photos the most suitable way is Equal ratio compression and Relative chromaticity then Absolute chromaticity is use in color theme for allowing the loss of local color and saturation priority is only suitable for a chart lines of graphic design work. For different color gamut chromatism which includes chromatism calculation in this we have to do calibration of two sample color according to L, a, b values and calculate the difference between Chromatism and individual by the formulas. The color information of digital image has minimum loses in different color gamut space but it shows the best color effect. [7]
Monitor Calibration and Characterization is done to resolve the color consistency of computer displays and digital printing. Calibrating the display under standard condition to display colors, color management software is used. In this white point setting and adjustment and Contrast and brightness adjustment is done then for different display the calibration and characterizations display is separate. The display profile as RGB color mode to achieve color consistency of different displays for the same RGB mode image is used. And again for digital press calibration and characterization is done using hardware and software. So according to color management mechanism the paper made a use of instrument for display calibration and characteristic for ensuring the color display in the standard condition. For the Bizhub pro C6501 digital press calibration and characteristic using of ICC profile for display and digital press in RGB and CMYK mode of prepress software, and then convert color space of the original manuscript into CMYK mode. So, the color became dim and the correct image color is accepted and printed. After printing, the difference between the actual output color and the original display color under the digital press color gamut space is identified. So from this it provides an effective solution for the color consistency. [8]
The color reproduction in terms of color difference and color consistency using the software and then check the effect of this software and proofing substrate on proof quality. Two types of custom semigloss art proofing paper is compare with two commercially available proofing software. After this combination of different substrate and proofing module should be tested with profile modules with the device that is profiled as CMYK device with charts of different module then calibration setup is created with two proofing device. And then generate the values and load it in proofing module to achieve better reproduction of color. The selected spot colors shows different behaviour when different combination is used and in digital proofing with custom proofing media color reproduction is mainly affected by proofing module. So without using manufacturer recommended proofing papers the appropriate module which reduces the costing of the proof is achieved with the results and Consistent Proof quality for spot colors is only achieved by standardizing a proofing process. [9]
The accurate color matching can be achieved for spot colors by digital proofing in commercial prepress system by illustrating the problems and reasons while outputting the spot colors. For that firstly select 18 basic color codes for maps in that some are spot colors and some are process color then open this patches in Photoshop and set their L*A*B values and then transfer it to CMYK color mode using default color setting and save in tiff file. The colorimetric values of the original is transformed in the custom color settings and the almost the same result is found in which the average color difference is very less and another reasons is that the only device settings of output plan template in the software is needed rest parameters are kept as default settings and several proofing correction are accurate in matching. [6]
The reproduction error in a different color gamut based on digital image color through different color gamut mapping method image processing software can be done by obtaining the corresponding image effect in which 4 gamut mapping ways is selected in Photoshop respectively corresponding to the color space conversion and then print the output. So for handling photos the most suitable way is Equal ratio compression and Relative chromaticity then Absolute chromaticity is use in color theme for allowing the loss of local color and saturation priority is only suitable for a chart lines of graphic design work. For different color gamut chromatism which includes chromatism calculation in this we have to do calibration of two sample color according to L, a, b values and calculate the difference between Chromatism and individual by the formulas. The color information of digital image has minimum loses in different color gamut space but it shows the best color effect. [7]
Monitor Calibration and Characterization is done to resolve the color consistency of computer displays and digital printing. Calibrating the display under standard condition to display colors, color management software is used. In this white point setting and adjustment and Contrast and brightness adjustment is done then for different display the calibration and characterizations display is separate. The display profile as RGB color mode to achieve color consistency of different displays for the same RGB mode image is used. And again for digital press calibration and characterization is done using hardware and software. So according to color management mechanism the paper made a use of instrument for display calibration and characteristic for ensuring the color display in the standard condition. For the Bizhub pro C6501 digital press calibration and characteristic using of ICC profile for display and digital press in RGB and CMYK mode of prepress software, and then convert color space of the original manuscript into CMYK mode. So, the color became dim and the correct image color is accepted and printed. After printing, the difference between the actual output color and the original display color under the digital press color gamut space is identified. So from this it provides an effective solution for the color consistency. [8]
The color reproduction in terms of color difference and color consistency using the software and then check the effect of this software and proofing substrate on proof quality. Two types of custom semigloss art proofing paper is compare with two commercially available proofing software. After this combination of different substrate and proofing module should be tested with profile modules with the device that is profiled as CMYK device with charts of different module then calibration setup is created with two proofing device. And then generate the values and load it in proofing module to achieve better reproduction of color. The selected spot colors shows different behaviour when different combination is used and in digital proofing with custom proofing media color reproduction is mainly affected by proofing module. So without using manufacturer recommended proofing papers the appropriate module which reduces the costing of the proof is achieved with the results and Consistent Proof quality for spot colors is only achieved by standardizing a proofing process. [9]
References
1. Introduction Quality managed proofing International IARIGAI Research Conference, September 8-11, Retrieved from https://www.color.org/proofing.pdf
2. Introduction 2002 Switserland, Guangdong Jinfuyuan textile printing machinery company limited http://gd-jfy.com/en/NewsShow.asp?id=160
3. What is Digital proofing of Spot color And Digital Proofs? China Grand Rise Packing Printing Co.,LTD Retrieved from https://www.lxpack.com/en/new/new-92-464.html
4. What is Digital Printing of spot color? Introduction to Digital Printing Technology by Vince Cahill,Owner The Colorworks Retrieved from https://docplayer.net/14399669-Introduction-to-digital-printing-technology.html
5. Hong S., Kai L., En Y., Hong C. (2012) Study on Color Management of Digital Proofing. Applied Mechanics and Materials, Vols 182-183, Trans Tech Publications, Switzerland, PP 352-356. Retrieved from https://www.scientific.net/AMM.182-183.352
6. Liu S., Sun Q., Wei B., Chen W. (2008) The Research of Map Spot Colors Digital Proofing in Commercial Prepress System. Society for Imaging Science and Technology, Retrieved from http://www.imaging.org/site
7. Wenge C. (2012). Study on Reproduction of Color Information of digital image Based on different color gamut Advanced Mechanics and Materials, Vols 430-432, PP 838-841, Trans Tech Publications, Switzerland, Retrieved from https://www.scientific.net/AMR.430-432.838
8. Zhao Y. (2015) Color Measurement and Analysis Based on the Konica Minolta Bizhub Pro C6501 Digital Press. Applied Mechanics and Materials Vol. 731, PP 62-67, Trans Tech Publications, Switzerland, Retrieved from https://www.scientific.net/AMM.731.62
9. Abhijit L. (2013) Attributal Standard Establishment For Spot Colors Accomplished Through Digital Proofing. IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE) ISSN: 2278-1676 Volume 4, Issue 2, PP 38-40. Retrieved from http://iosrjournals.org/iosr-jeee/Papers/Vol4-issue2/F0423840.pdf
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