Four-color Printing Research Articles

Study of correlation between ink trapping and color difference in overprint

The ink trapping value is one of the important parameters affecting the appearance of secondary colors in overprint. Usually, the ink trapping parameter is traditionally calculated based on the solid density values of the primary colors and the overprint color. These density values are measured by the complementary color filter of the color final ink layer, and these ink trapping values can be calculated using the Preucil, Ritz, or Brunner formulas. Furthermore, the density measurement is more suitable for testing the color printing and not for overlapping assessment because these density values are measured by the complementary color filter of the second color ink. The ink has a specific transmittance, and light is not only absorbed but also scattered inside the ink layer, so the total density of the overlapping colors will be less accurate. As a result, the color measurement method is used to describe the effect of ink trapping of the second ink layer on the first layer of ink. The main idea is to use the color difference value to evaluate the ink trapping ability. In this paper, the author has quantitatively analyzed the correlation between the percentage value of ink trapping and the color difference parameter ΔEab*. The studied results show that the ΔEab* value has a linear correlation with the ink trapping value calculated according to the traditional methods based on density values. This result is also aimed at the fluctuant tolerance of ink trapping ratio during four-color printing to achieve the standard color value quickly.

Research on Multi-Color Separation Model Based on Polynomial Regression

In order to improve the quality of prints, we usually add additional OG or RGB ink on the basis of the four-color printing ink (CMYK) to increase the printing color gamut. After that, the conventional separation technology is no longer suit for multi-color printing, so the multi-color separation technology is put forward. Currently, the main multi-color separation method is color partition technology. It divided the color space into five or six partitions. Then each partition was subdivided into several cells, and then established the polynomial color separation model for each cell. In this paper, we improved the selection of samples and cell search method. The experimental results showed that the color separation algorithm had high color separation accuracy and stability and could meet the demand of high precision multi-color printing.

Study on Tent Cloth Materials for Desert Type Camouflage

In order to solve the problem of quickly fading on tent cloth material, this paper presents a new formulation of a four-color printing coating on inorganic pigment. As an actual application, the desert type camouflage coating is tested and completed. At the same time, this paper adopts a new method to design a digital camouflage based on the natural background. That is to extract main colors of background using clustering segmentation, as well as fill in the camouflage spots using mosaic blocks. The test demonstrates that, after the designed desert pattern is printed on the tent cloth, the tent made from the tent cloth is placed into the desert background. It can reach a good camouflage effect.

Ranked dither for high-quality robust printing

A robust parallelized halftoning method is proposed that is insensitive to dot loss, which can be a problem with xerographic and high-resolution printing. The method uses standard clustered-dot dither for smooth image blocks but uses the rankings of dither thresholds to halftone image blocks with high spatial activity. Experiments compare the ranked dither to dither, error diffusion, and green-noise error diffusion for four-color printing using standard clustered-dot dither masks at standard angles for the cyan, magenta, yellow, and black planes, respectively.

Enabling Expanded Color Gamut and In-line Coating Processes

Most four-color printing processes that are extensively used in electrophotographic (EP) applications today are based on the SWOP (Specifications for Web Offset Publications) colorants. Although, this set of colorants offers many advantages, it fails in many aspects as it does not deliver many often requested colors in digital printing. For example, most corporate identity colors cannot be faithfully reproduced with the available gamut possible with this color set. Most attempts to increase the color gamut by selecting high chroma colorants only provides marginal improvements. At the same time these colorants can have high impact on toner performance developer life. Many of the limitation of a four color system can be addressed by a adding fifth module in the digital color press. One such digital press now commercially available, is NexPress 2100. By proper selection of fifth color DryInk™ or toner, and utilizing pentachrome process, Nexpress 2100 digital press manages to expand color gamut on demand while still continuing to utilize the standard CYMK toners. The result is a low cost solution to matching most colors that are often demanded by customers. With the availability of fifth module, it is also possible to use it to apply a clear overcoat in an intelligent manner. Such a coating process is truly inline and offers efficient workflow solutions. Clear Overcoats provides superior protection and enhance many image quality attributes. Many capabilities and limitations of fifth module will be presented. Impact on EP process and color gamut by the colorant selection will also be discussed.

新聞におけるカラー印刷の進展と現状

20 years ago, few newspapers printed copies with four-color printing because of the technical limitations of the pre-press and printing press. Since the introduction of computerized pre-press systems and automated plate-making and printing equipment, you probably see four-color items on most newspaper everyday.Once the color reproduction process required experts. Now computerized color processing technology makes it editors' jobs. They choose a favorite picture on a display screen and then hit a command button to transmit it to a designated page. When the development of a new advertisement system is completed, which gets originals with digital form via web from advertisement agencies, process time required for putting an advertisement on a page will be shortened and the quality of printings would be better.Japanese newspapers utilize offset presses for four-color printing in general. Satellite type machines were dominant in the past. A tower type machine appeared in the Japanese market 4 to 5 years ago and it thrives at present for the space efficiency and more color pages.

Color Correction in Color Printing1

In a three-color print, the color of any area that is large in comparison with the size of the dots of the structured image can be regarded as an additive mixture of eight colors: the unprinted paper stock; the cyan, magenta, and yellow of the individual ink dots; the red, green, and blue that result when ink dots overlap in pairs; and the black that results when all three ink dots overlap. Since the extent of overlapping is determined by the sizes of the dots, the color of the additive mixture can be expressed by three equations. The straightforward attack on the problem of color reproduction is to solve these fundamental equations for the required dot sizes on the assumption that, in every area, the tristimulus values of the reproduction should be equal to those of the original. This has not been accomplished hitherto, because it involves solving three simultaneous equations of third degree, each containing eight terms. However, a relatively simple electronic equation-solving network has been constructed which solves these equations with ample precision in 0.001 second. By using this network in connection with a scanning machine of the type described in the preceding paper, full color correction is achieved. A corresponding set of equations can be written for the additive mixture produced in four-color printing, wherein the fourth color is black. Since the three equations now contain four unknowns, an additional condition must be imposed. From the standpoint of the printing requirements, it is desirable that at least one of the color dots be absent, or of some predetermined minimal size, in every region of the reproduction. An extension of the principles embodied in the electronic network mentioned above imposes this condition and yields a continuous solution to the three fourth-degree equations.

Photography as Used in Color Reproduction in the Graphic Arts: The Three-Color Theory of Vision—Making Photographic Materials Sensitive to Colors—Natural-Color Photographs—Color-Separation Negatives—Printing Processes—Modern Four-Color Printing Presses and Their Interesting Devices

Abstract Indications are that the demand for color in the graphic arts, produced by means of photography, will continue to increase, and this means that as the fundamental principles appear to be well established, further improvements will be made in machinery and materials and the skill in using them; and particularly in adjusting practice as closely as possible to theory, so that color reproduction, while maintaining the highest possible quality, will be produced more speedily and more economically.