Printing Press Guide
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Properties of Color
An understanding of color is very crucial in the multicolor commercial printing world. This ensures that your publication comes out with the expected colors. Color has three main components, namely, value, saturation, and hue.
The wavelength of light transmitted through or reflected from an object is referred to as hue, and this is what identifies a color as being blue, yellow, green, etc. The lightness or darkness of hue is termed as the value of color, while the dullness or vividness of hue is termed as saturation, otherwise known as Chroma.
Color perception is affected by many factors. The color we perceive on computer monitors may be different when printed because monitors use additive RGB (Red, Green, Blue)color mixing techniques to produce different colors. Simultaneously, the printing press employs the use of subtractive CMY(Cyan, Magenta, Yellow) color mixing to create different colors.
Printing Terminology
A continuous tone art is an original painting, photograph, or drawing. Color is broken down into dots of various shapes and sizes, known as halftone screens, to reproduce a continuous tone art in a commercial printing press. Premixed inks are used to produce spot colors on a printing press using a single plate for each color. By printing halftone screens of CMY inks to simulate many different colors, process colors are reproduced.
Gray component replacement (GCR) and under color removal (UCR) are used in process color production to reproduce black color. In these methods, black ink replaces amounts of cyan, magenta, and yellow inks. Shadow areas are deepened primarily by UCR, while an appropriate part of black replaces all neutral color areas in GCR.
The colors on the other separation are knocked out by the top object by default when color separations for a document with overlapping color are being imaged—overprinting, which is the practice of printing individual items on top of any elements behind them. This can be used to create special effects against background colors or as a method of preventing small gaps from appearing between colors or objects due to press misalignment.
Common Printing Problems
It is said that human is to error, and so is his/her creation; in the printing press world, this statement is also applicable. The common problems experienced in printing include Moiré patterns, misregistration, and dot gain.
In the printing process color separations, each process ink’s dots are positioned at a specific angle for the ink dots to form a pattern that is not distracting to the eye. The dot rows are placed to create a rosette pattern merged by the eye into continuous-tone color. If the printing paper shifts as it goes through the printer or process ink prints at an incorrect angle, the rosette pattern is distorted to form a moiré pattern that disrupts smooth color gradations perception.
As paper absorbs moisture and is pulled through a printing press, it sometimes shifts and stretches .stretching, and printing plates can also experience misalignment. These may lead to hue shifts or slight Gaps between colors that overlap due to multicolor jobs printing out of register. This is termed misregistration.
The printed dots’ size is affected by many factors, including paper type, press type, and the photochemical processes used to produce separations. When wet ink spreads as the paper is absorbing it and when negatives from different sources are being duplicated, the dots’ size increases. This is what is called dot gain, and it leads to images and colors printing darker than they are desired.
Emerging Printing Technologies
Technology is never static, revolutionary changes are being experienced in every aspect of science and technology as more ambitious scientists and entrepreneurs come into being. This is also true in the printing world, where several new technologies are emerging. These technologies include direct digital printing, color management systems (CMS), high fidelity color printing, and frequency modulation screening.
In direct digital printing presses do not require films or sometimes even plates. They are connected to workstations, which create PostScript files from digital files, screen bitmap images, and sent the files to the press. Direct digital processes that do not require plates transfer digital information to electro-photographic cylinders and use toner to print. In contrast, others send the digitized pages directly to special plates mounted on the press. This printing process results in low costs, fast turnaround, an easily personalizable design
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Software that interprets color between different devices such as color monitors, printers, and scanners is called a color management system (CMS). This uses a device profile to map colors from one device’s color gamut into a device-independent color model then maps the colors into another device
‘s color gamut.
New and not yet widely available, high fidelity printing employs different process inks in reproducing more of the color spectrum. High fidelity color can be printed with at least five inks on existing printing presses.
By controlling the number of dots in each area, frequency modulation printing, also known as stochastic screening, renders different shades of an image. The more the dots, the darker the site, and vice versa. To FM screening, it requires an imagesetter raster image processor (RIP) that supports it.