An Evaluation of the effect of registration on GCR and conventional chromatic separation methods in multicolor halftone printing

Misregistration is an unavoidable problem in multicolor halftone printing. It causes the loss of detail, sharpness and color hue shift of a reproduction. However, there is a color separation technique called Gray Component Replacement (GCR) which may reduce or eliminate this misregistration effect. An investigation had been conducted using a series of color halftone proofs which were produced by conventional chromatic and GCR color separation techniques. The subjective image quality scaling method was applied to this study as a criterion to determine whether there is an image quality relationship between these two techniques on misregistered reproductions

The effect of solid ink density on shifts in hue in gray component replacement

With advances in computer storage and electronic dot generation scanners a new color separation process has become possible. Although in theory the Gray Component Replacement (GCR) process has been possible since the early twenties, it has only recently been available through contemporary color separation methods. GCR is the process by which the gray component of a particular color reproduction is removed from the reproduction and replaced with black ink. The gray component is defined as specific combinations of the least predominant color and the other remaining inks. A printing form was designed to include three different color reproduction processes: the 100% GCR, 60% GCR, and normal chromatic. A standard color transparency used for color evaluation was included with a series of 24 color test patches. A colorimeter was used as the test instrument, and the color patches provided ease in measurement using the instrument. The form was mounted on the lithographic press and the press was run to match the proof. Once a color OK was obtained and samples obtained, ink densities of the other units were selectively varied to provide a shift in hue. A colorimeter was used to obtain a value of Delta hue from the selected press sheets. Each standard color press sheet was measured and recorded as a standard with successive readings measured in terms of Delta hue. The color test patches were divided into groupings of neutral gray, hard to print, process/overprint, and all colors. Each Delta hue measurement was recorded and grouped into the specific categories. The variations of the normal chromatic and the 100% GCR separations were compared, as well as the variations of the normal chromatic and the 60% GCR process. This is to say that the neutral gray color grouping compared the measurements of the 100% GCR to the measurements of the normal chromatic process. These same measurements were taken for each variation within each color grouping. Delta hue readings for each of the color groupings was used to calculate a t-value and test the significance of the difference between the different processes. If there was indeed a difference between the different processes then a t-value of 1.65 would result. A level of significance of .05 was obtained in all of the comparisons. The GCR does reduce shifts of hue on the lithographic press. This reduction in shifts of hue should relate to an increase use of the GCR process in the future

The Effects of fluctuations in solid ink density on color variation for conventional and grey component replacement separations when printing process color on newsprint

A color separation technique known as Gray Component Replacement, or GCR has been an option available to high-end drum scanner operators for the past eight years. Recently, GCR has been made available by lower-end color system vendors as well. GCR consists of removing the least predominant process color ink in a unit area, reducing the remaining colored inks by the same amount and replacing the gray component of the color with black ink. One of the reported benefits of the GCR technique is that more consistency can be realized during a pressrun. If this is in fact true, the first publication printers who would surely utilize the technique would be newspapers. The problem of consistency is particularly acute for newspapers. There are a number of reasons for this, but the primary ones relate to the types of materials used. Newspapers use the cheapest paper and ink and in many cases, they print with old or poorly maintained presses. They would surely welcome any process that offered better reproductive quality and more consistency, provided the investment was justifiable. Since their present color separation systems allow for the use of GCR in the majority of cases, its potential in the area of newspaper printing was investigated in this study. One factor determining consistency during a pressrun is the control of ink film thickness. As ink film thickness fluctuates, color variation takes place. This study compared the amount of color variation realized for a conventional separation and GCR separations as ink film thickness was varied on press. A separation was made conventionally and with five levels of GCR (however only 40% and 80% could be used for analysis). A Macbeth color checker, comprised of twenty-four color patches, was used as the test target. Ink film thickness was varied to three fluctuation magnitudes. Twenty-five press sheets were chosen from the fluctuation cycles. A spectrophotometer was used to obtain color difference magnitude data (AE) between the ink variation sheets and a sheet with nominal solid ink densities for both the conventional and GCR separations. A mean AE value was tabulated for each group. The GCR mean values were compared to the conventional mean value. Using both the z-Statistic (for multi-sheet comparisons) and the Student\u27s t-Statistic (for single sheet comparisons) tests were performed to determine if the difference in color variation between the conventional separation and the GCR separations was significant statistically. The t-Tests indicated that less color variation was realized for the GCR separation if the level of GCR was substantial (80% as opposed to 40%). Where the data was deemed valid, no cases existed where less color variation was realized for the conventional separation. The initial z-Test (when the number of samples was 192) revealed less color variation for the GCR separations and higher color variation for the conventional separation. The final z-Test (including all sample press sheets) revealed much less color variation for the GCR separations compared to the conventional separation. The amount of color variation was higher for the GCR separations compared to the conventional separation only in cases where the black ink film thickness was varied. However, in these cases the difference between the conventional and GCR color variation means (mean AEs) revealed that the difference was not statistically significant

The effects on hue resulting from black overprinting in halftone reproductions

A type of black printer that only existed in theory is now being applied in the printing industry. The process which makes use of this black printer is known as gray-component replacement. Developed from the extension of the undercolor removal process, the use of gray-component replacement in printing halftone reproductions is said to result in numerous technical and cost benefits. When used to the maximum, the process eliminates one of the three process color inks in a given unit area and prints black ink from highlight to shadow. A problem can result from the use of this process as it applies a greater amount of an opaque black ink in combination with selectively transparent colored inks. Where this black ink overprints one or more of the three colored inks there will be an increase in unwanted absorption and a decrease in the wanted absorption. The result of such overprinting will be the alteration of the reflectance curve of the reproduction as compared to the original with the result being a shift in hue. An experiment was performed to demonstrate the principles. Several tint patches were printed with the only difference between each patch being the location of black ink overprinting within the tint. It could be seen by visual analysis that a hue shift did occur. Sample tint patches were analyzed by means of a spectrophotometer to objectively describe the visual results

A Colorimetric performance comparison of gray component replacement algorithms

An experiment was performed to compare the effect of gray component replacement on color separations created with the Hell 399ER scanner software compared to two desktop algorithms. Three different GCR methods were tested; the scanner method where the separations were performed and films output on a mid 1980\u27s model Hell 399ER laser scanner using Hell\u27s first generation GCR algorithm and two types of desktop methods where the scans were done in RGB, color separated on the desktop, and films generated on an Agfa Selectset 5000 imagesetter. The two desktop methods used were RIT Research Corporation\u27s RGB-CMYK transform and Adobe Photoshop 2.0. All scans and proofs were made in the Color Separation Lab at the Rochester Institute of Technology (RIT) in Rochester, New York. The desktop separations were made and film output in RIT\u27s Electronic Prepress Lab. For each separation method, three levels of GCR were performed; a non- GCR (0%) separation, one at 50% GCR, and one at 80% GCR. In addition, the separations performed on the Hell Scanner were done with Under Color Addition (UCA) off and on. After separation, the scans were output to film and proofed using 3M Matchprint II. Two proofs were made. One contained the six separations performed on the Hell scanner and the other contained the six separations made using the desktop software. The proofs were then measured using a spectrophotometer and the results compared using the L*a*b* color space. All color comparisons were done using the non-GCR separation as the color reference. Each AE* measurement represents the color difference between a patch on the non-GCR target and the corresponding patch on the target produced using GCR. The result of the experiment was the rejection of the stated hypotheses that there would be no significant color difference between the output produced from the scanner separations and the desktop separations at two levels of GCR. The experiment showed that the algorithms used to perform GCR on the desktop produced less color variation than the algorithm used in the Hell 399ER scanner at both 50% and 80% GCR. The results also showed that in almost every case, the amount of color variation increased as the level of GCR was raised. It could not be determined whether or not Under Color Addition (UCA) had any significant influence on color variation for the separations performed on the Hell scanner. Based on the results of this experiment, color professionals using a desktop production workflow should be encouraged to take advantage of the benefits of GCR without fear that the color of the reproductions will be compromised

Comparison of color lightness in two-color plus black reproduction systems vs. three-color reproduction systems

A theory that has existed since 1948 has just recently gained wide acceptance from the printing industry. The recent technological advancements in electronic scanners has made it feasible for color separations to be scanned implementing Gray Component Replacement (GCR) . Eventhough most of the electronic scanners today have GCR capabilities, some questions regarding GCR and its implementation have gone unanswered. In an attempt to help resolve this problem, this paper investigated the issue of lightness characteristics associated with GCR reproductions. In particular, this paper attempted to prove that, by replacing a graying component of a conventional reproduction made up of three transparent inks with a black ink in proportional amounts, less light would be scattered within the paper and trapped by the ink due to less ink coverage. Accordingly, the less light trapped under the ink, the closer that reproduction would be to the original in lightness. The results of the experiment proved that GCR is not as simple as some believed it to be. In addition, two experimental errors made it difficult to support the hypothesis

Pengaruh Level GCR dan UCR dengan Pengaturan Total Ink Limit Terhadap Penyimpangan Warna

Keakuratan warna abu-abu berperan penting dalam pengendalian kualitas warna suatu cetakan. Hal ini karena warna tersebut terdiri dari warna cyan, magenta dan yellow untuk melihat karateristik warna CIEL*a*b. Kalkulasi warna abu-abu ini dapat diatur dengan metode gray component replacement (GCR) dan under color removal (UCR) pada kegiatan pracetak dengan cara mengatur level total ink limit pada printer. Maka tujuan dari penelitian ini adalah untuk mendapatkan level GCR/UCR yang memiliki ∆E a*b terkecil dengan pengaturan total ink limit dan nilai deviasi warna (∆E a*b) dengan 3 variasi pengaturan total ink limit (200%, 300%, 400%) pada target warna FOGRA 27. Hasil penelitian ini menunjukkan bahwa komposisi CMYK ink coverage level GCR/UCR menunjukkan perubahan deviasi/penyimpangan warna (∆E a*b) neutral gray (mid tone) menggunakan FOGRA 27, memperlihatkan bahwa semakin tinggi total ink coverage maka semakin banyak tinta CMYK yang digunakan. Dan nilai deviasi warna (∆E a*b) terkecil adalah GCR Medium 400% dengan nilai ∆E a*b = 3,0 dan nilai penyimpangan warna UCR terkecil sebesar 1,67