Reduction of Process-Color Ink Consumption in Commercial Printing by Color Separation with Gray Component Replacement Suchapa Netpradit*, Wittaya Kaewsubsak, Peerawith Ruvijitpong and Thanita Worawutthumrong Department of Printing and Packaging Technology Faculty of Industrial Education and Technology King Mongkut s University of Technology Thonburi 126 Pracha-Utit Rd., Bangmod, Thungkru, Bangkok 10140, Thailand Corresponding author s e-mail: suchapa.net@kmutt.ac.th Abstract: Gray Component Replacement (GCR) is a technique for making color separation plates in the printing process by replacing cyan (C), magenta (M) and yellow (Y) inks with black (K) ink throughout the image, in order to reduce the amount of expensive process-color inks. In this work, different levels of GCR were studied at 0, 50, 70, 80 and 90% by using the software of color management system. Total ink coverage was set under 280% and various GCR levels were compared with the original image on the soft proof. The tone reproduction curves and the affected image qualities were also determined. After selecting the optimum GCR level, the large format inkjet printer was taken to proof in accordance to a profile of web-fed offset press to check the color image qualities. The color separation plates were then made using the best GCR level compared with the normal technique (no GCR). The real print work was performed on the commercial web-fed offset press by using newsprint paper to observe printing condition, printed image qualities and ink consumption. This study showed that GCR level of 80% was the best level to greatly reduce CMY inks but offered more color saturation, detail and contrast. Total color difference of printed images between normal and GCR was very little (ΔE* 2.12), measured by a spectrophotometer. In the consumption of inks, the amount of black ink was increased at 65.60%, but cyan, magenta and yellow ink was reduced at 18.10%, 4.02%, and 7.86%, respectively. The ink price at the present time indicated that around 5% of ink cost could be reduced. Therefore, GCR is a good technique for color separation in printing process with the similar color printed images, the faster ink drying and the lower ink cost. Keywords: Color separation; Commercial printing; Gray Component Replacement; Ink consumption; Process-color ink 1. INTRODUCTION Color printing is the reproduction of an image or text in color by using cyan (C), magenta (M), yellow (Y) and black (K) inks (often referred to collectively as CMYK), which need a color separation process to divide colored artwork into 4 printing plates. In gray component replacement (GCR), the values of 3 subtractive primary colors (CMY) that add to gray all along the tone scale can be replaced with the black ink [1]. If the color is not too dark or too saturated, the equivalent amount of CMY in color areas should be removed and replaced with K in the same percentage of any removed color. The GCR technique uses more black ink on color areas that are not neutral and tends to work better for images that have dark colors. Using a unit amount of black ink rather than 3 unit amounts of CMY inks can lead to significant cost savings, especially because black ink is often less expensive than any of the color inks [2]. In addition, printing with high amount of CMY color inks together merely to make gray can make the paper rather wet, which is a problem in high speed commercial web-fed printing where the paper must dry extremely rapidly to avoid marking the next sheet, and the poor quality paper such as newsprint may break if it becomes too wet. In Thailand, offset printing is the most common form of high volume commercial printing, due to advantages in quality and efficiency in high volume jobs. Presently, many commercial printing factories that install the web-fed offset presses are continually trying to increase the printing productivity, improve the printed image qualities, and reduce the production cost. The purpose of this project is to make a guideline for the printing industry to improve the printing production system by using the best technique of color separation in the prepress step. Since the amount of black to use to replace amounts of CMY inks is variable and the optimum GCR level is depended on the technology, paper and ink in use, the optimum GCR level for a printing condition should be previously analyzed because too high level of GCR may make some colors appear dirty or shift. The case study on the application of color separation with GCR technique was also performed on the real printing work in a commercial printing company to determine the results between the normal and the GCR techniques, in term of printed image qualities and process-color ink consumption.
2. EXPERIMENTAL 2.1 Making the Profile of Web-fed Offset Press The test form of ECI 2002 providing 1,520 color patch chart was used as an original to print on the newsprint paper by the commercial web-fed offset press (KBA COMPACTA 215). Some optimum quality print sheets of test form were taken to measure the CIE L*a*b* color values of all color patches with a scanning spectrophotometer. The resultant color values were compared with the reference color values to find the print profile of the commercial web-fed offset press by using the profile maker software (Printopen 4.0.5). The print profile of the studied web-fed offset press was stored for further color separation and simulated for output by digital proofing either monitor or inkjet printer. 2.2 Selection of the Optimum GCR Level The color separation was prepared by setting the level of GCR at 0, 50, 70, 80 and 90% under the total ink coverage of 280% (U280). More level of GCR, more removal of cyan, magenta and yellow colors, and more adding of black color. However, the best GCR level must be selected from the inkjet proof sheets in accordance to the web-fed offset press to determine the most CMY color reduction and the same appearance to the normal image (no GCR) in terms of color gamut, detail and contrast. 2.3 Case Study of the Real Printing Application After the best GCR level under the total ink coverage of 280% was selected, the color images of a real brochure with the print profile and optimum GCR setting were assembled on a lay-out size of 1010 x 655 mm by processing in Photoshop program. Two sets of color separation plates; the normal (no GCR) and the GCR setting, were then made for further real print test on the newsprint paper by the commercial web-fed offset press in a printing factory. The printing qualities were checked and controlled under the in-house standard by sampling the printed paper every 5,000 impressions. 2.4 Evaluation of Reproduction Quality and Satisfaction The printing qualities; solid color density, dot gain, print contrast and ink trapping on the control strip of the printed sheet samples were measured with a reflection densitometer. The color difference (ΔE*) of several color images between the normal and the GCR were also measured with a spectrophotometer using CIE L*a*b* color space. The satisfaction of the color images with GCR setting was also evaluated by using the questionnaire as a tool for the sample group of 40 observers in the printing field included of 10 experts, 10 lecturers and 20 graduate students. 2.5 Estimation of Process-color Ink Consumption and Cost Saving The individual cyan, magenta, yellow or black ink consumption was measure by weight and the transfer rate of ink unit was also determined, which were compared between before and after using the GCR technique. The different data was calculated and the change in ink cost was estimated referring to the ink price at the present time. 3. RESULTS AND DISCUSSION 3.1 Comparison of Tone Reproduction with Various GCR Levels The CMYK tone reproduction curves of GCR setting at the level of 0, 50, 70, 80 and 90% are shown in Figure 1. The results presented that the curves of C, M and Y colors were gradually moved lower while the curve of K color was raised upper from the highlight tone toward the shadow tone when the level of GCR setting was increased. In addition, the color separation of a bottle picture with various GCR levels is also shown in Figure 2. This informed that the cyan, magenta or yellow tone values in dark area of a bottle were decreased while the tone of black color was darker when the GCR level was increased.
No GCR GCR 50 GCR 70 GCR 80 GCR 90 Figure 1. Tone Reproduction Curves of CMYK Color Separation with Different GCR Levels No GCR GCR 50 GCR 70 GCR 80 GCR 90 No GCR GCR 50 GCR 70 GCR 80 GCR 90 Cyan Color Magenta Color No GCR GCR 50 GCR 70 GCR 80 GCR 90 No GCR GCR 50 GCR 70 GCR 80 GCR 90 Yellow Color Black Color Figure 2. CMYK Color Separation Images with Different GCR Levels
However, the CIE L*a*b* color gamut of images with any level of GCR setting was not significantly different. It is visible that all the four-color images either without GCR or with GCR at different levels were reproduced in the same (Figure 3 left). The color gamut of images using GCR technique seem to be slightly wider than the one without GCR setting, as shown in Figure 3 (right), indicating that some colors in the image might appear more saturation. b -a a No GCR GCR 50 GCR 70 GCR 80 GCR 90 -b Figure 3. Four-color Images with Different GCR Levels (left) and CIE L*a*b* Color Gamut (right) of the Image without GCR (white line) and GCR 80 (Gray line) Although the GCR at a level of 90% could provide the highest reduction of CMY colors, the detail and dimension of color picture was poorer than the GCR level of 80%. Therefore, GCR 80 was selected to set in a profile of color separation for this case study because it could highly reduce CMY colors while the reproduced color and quality were not changed. 3.2 Qualities of Printed Sheet Samples The qualities of the printed sheet samples were controlled under an in-house standard of the printing factory. The printing conditions of all works in this case study were set in the same. The average data of the acceptable quality samples were measured as shown in Table 1, indicating that the printed samples were acceptable for further evaluation. Table 1. Qualities of Process-color Printed by a Web-fed Offset Press Print Qualities Cyan Magenta Yellow Black Standard Solid Density 1.20 ± 0.05 1.20 ± 0.05 1.00 ± 0.05 1.50 ± 0.05 > 1.00 Dot Gain at 70% Tone 22% 21% 17% 20% < 25% Print Contrast 24.7% 31% 32.5% 49.3% 30% Ink Trapping M on C = 56% Y on M = 55% Y on C = 68% - 60% 3.3 Color Difference between Normal and GCR Color Separations The color samples of printed images were observed in the area that contained 3 process-colors in the composition. The color difference values of the selected 14 colors in many pictures on the printed sheet between the normal and the GCR were then measured as shown in Table 2. The average value of color difference was very little (ΔE* = 2.12) and almost all color reproduction of GCR setting was within or near the acceptable boundaries because the values of ΔE* 3 have been considered as the threshold of acceptability [3].
Table 2. Color Difference (ΔE*) between Normal and GCR Measured on 14 Color Samples Color Sample C (%) M (%) Y (%) K (%) ΔE* 1 5 30 90 5 0.805 2 100 60 90 10 0.872 3 5 100 30 0 3.516 4 50 60 70 80 0.653 5 30 10 20 80 3.659 6 90 5 100 25 2.603 7 10 100 90 10 2.366 8 5 30 90 0 2.472 9 90 0 10 0 3.909 10 90 20 100 70 1.248 11 90 100 20 20 2.546 12 0 100 40 20 2.241 13 80 70 90 30 1.159 14 100 100 100 90 1.659 Average ΔE* 2.12 3.4 Visual Evaluation by a Sample Group of Observers Based on the visual evaluation of the observers, Figure 4 indicated that the printed images reproduced by GCR technique were much more satisfied by a sample group of 40 observers than did the normal images in saturation, hue, contrast, sharpness and detail, while the satisfaction in brightness of pictures reproduced by GCR was reasonable. However, these results suggest that the color separation with GCR technique had a high trend for real application in all printing factories. 90% 87.5% 90% 87.5% 85% 87.5% 60% 40% 10% 12.5% 10% 12.5% 15% 12.5% Saturation Hue Contrast Sharpness Details Evaluation of Print Qualities Brightness Satisfy No GCR GCR 80 Figure 4. Visual Evaluation by a Sample Group of 40 Observers 3.5 Process-color Ink Consumption and Cost Saving The ink consumption of the real printing work was compared between the normal color separation and the GCR color separation and the printing ink costs were then estimated as shown in Table 3. Although the black ink consumption was increased, the consumption of 3 process-colors was much decreased, resulting in the reduction of total ink consumption
and ink cost. It was shown that the total ink cost was reduced around 919.40 Thai Baht while the initial cost of all process-color ink consumption for 100,000 printed sheets was around 18,570 Thai Baht (only for this case study). Therefore, the calculated cost saving was around 5% after using the GCR technique in the color separation process. Table 3. Ink Consumption and Ink Cost Saving Estimated from 100,000 Printed Sheets after Using GCR Technique Ink Color Ink Consumption with no GCR (Kg) Ink Consumption with GCR (Kg) Ink Consumption Change (Kg) Ink Consumption Change (%) Ink Cost Difference (Thai Baht) Cyan 15.75 12.90-2.85-18.10-513.00 Magenta 29.86 28.66-1.20-4.02-216.00 Yellow 55.95 51.55-4.40-7.86-748.00 Black 5.00 8.28 + 3.28 + 65.60 + 557.60 Total 106.56 101.39-5.17-4.85-919.40 * Minus (-) means decrease, Plus (+) means increase. 4. CONCLUSION As the results of this case study, GCR setting at the level of 80% was the best technique of color separation, presenting an optimum color reproduction that greatly reduced 3 process-color inks (CMY) while maintained the same color and image qualities. The printed images reproduced by GCR technique had little color difference from the normal technique because the average ΔE* < 3. The printing qualities were also much more satisfied by a sample group of observers than did the normal color separation. Although the black ink consumption was increased, the CMY color ink consumption was much more decreased, resulting in total cost saving of around 5% after using the GCR technique in color separation. This study could be a guide line for many printing factories to further improve the printing production system such as productivity increase and cost reduction. ACKNOWLEDGMENT The authors would like to thank The Thailand Research Fund for financial support. Thanks to Cyber Print Co, Ltd. for supporting the web-fed offset press and printing materials in this case study. Appreciation is due to Soonthorn Film Co., Ltd. for assistance in color separation process and providing plate-making. Special thanks to Miss Krittaya Watchagornamornchai and Miss Sirikanya Taosomta for helping in the experiment. REFERENCES 1. From Wikipedia, the free encyclopedia. http://en.wikipedia.org/wiki/gray_component_replacement 2. Swati B. and Subhendu M. (2000). Effect of Gray Component Replacement on Color Reproduction. In Proceeding of PICS 2000: Image Processing, Image Quality, Image Capture, Systems Conference, Portland, March, pp. 188-191. 3. Maja B. and Nina K. (2004). Colorimetric investigations as quality criteria of the work of art reproductions. In Proceeding of AIC 2004 Color and Paints, Interim Meeting of the International Color Association, pp. 167-170. 4. Helmut K. (2001). Handbook of Print Media: Technology and production Methods. Springer, Germany. 5. Bernard R. H. (1965). Color stripping for offset lithography. 2 nd ed., Graphic Arts Technical Foundation, Pennsylvania.