color printing Color printing or colour printing is the reproduction of an image or text in color (as opposed to simpler black and white or monochrome printing). History of color printing Woodblock printing on textiles preceded printing on paper in both Ea ...

, print registration is the layering of printed patterns to form a multicolor pattern. Registration error is the "position misalignment in the overlapped patterns." Machine components such as the print cylinder, doctor blade assembly, printing plates, stress/friction and more, affect the registration of the machine. Inconsistencies among these components can cause the printing press to fall out of registration; that is when press operators will begin to see defects in their print. There are many different ways to achieve proper registration, many of which employ the alignment of registration marks (pictured right). Many press manufacturers have installed automatic register systems to assist the operator in getting the print back into proper alignment.

Purpose

When printing an image or a package of some sort that has more than one color, it is necessary to print each color separately and ensure each color overlaps the others precisely. If this is not done, the finished image will look fuzzy, blurred or "out of register" (see image to right). If one or more print units, plate or other print component is out of registration, the result can be printed colors in the wrong areas, overprint or white space. With proper registration, there will be no white space, out of margin colors, or confusing overlap of images in the print. To help line the colors up correctly, a registration system is necessary.

Registration black

In printing, registration black is a black color that includes 100% of each of the process colors used. Typically these are

cyan Cyan () is the color between blue and green on the visible spectrum of light. It is evoked by light with a predominant wavelength between 500 and 520 nm, between the wavelengths of green and blue. In the subtractive color system, or CMYK c ...

magenta Magenta () is a purple-red color. On color wheels of the RGB color model, RGB (additive) and subtractive color, CMY (subtractive) color models, it is located precisely midway between blue and red. It is one of the four colors of ink used in colo ...

yellow Yellow is the color between green and orange on the spectrum of light. It is evoked by light with a dominant wavelength of roughly 575585 nm. It is a primary color in subtractive color systems, used in painting or color printing. In t ...

and

black Black is a color that results from the absence or complete absorption of visible light. It is an achromatic color, without chroma, like white and grey. It is often used symbolically or figuratively to represent darkness.Eva Heller, ''P ...

(

CMYK The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. The abbreviation ''CMYK'' refers ...

), but if different colors are used, registration black marks are made with all of the

colorant A colourant/colour additive (British spelling) or colorant/color additive (American spelling) is a substance that is added or applied in order to change the colour of a material or surface. Colourants can be used for many purposes including printin ...

s (inks). Registration black is used for printing crop marks and registration marks. When proofs for each color are generated on separate pieces of film, use of registration black makes crop marks visible on all channels, providing a useful reference for alignment. A thin line printed in registration black can also be used to check whether the printing plates are aligned.

PostScript

The

PostScript PostScript (PS) is a page description language and dynamically typed, stack-based programming language. It is most commonly used in the electronic publishing and desktop publishing realm, but as a Turing complete programming language, it c ...

printer description languages supports registration black, starting with PostScript language level 2. This is done by referring to a

spot color In offset printing, a spot color or solid color is any color generated by an ink (pure or mixed) that is printed using a ''single run'', whereas a process color is produced by printing a series of dots of different colors. The widespread offset- ...

with the special name All. This never generates a spot plate. Instead it marks all of the plates that are there. The All color space can be used with a tint value between 0.0 (no mark) to 1.0 (full intensity). Generally, only 1.0 would be used. The name "All" might not be used in the user interface of a design program, especially outside English language speaking areas. However, the spot color must have the exact name "All". As a side effect, it is impossible in PostScript to create a normal spot plate with this name.

PDF

The

Portable document format Portable document format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating syste ...

(PDF) also includes a spot color called All, with the same restrictions, starting with PDF 1.2. Note that a PDF spot color must also include a "tint transform" which translates spot values into a different

color space A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of colorwhether such representation entails an analog or a digital represe ...

for viewing on screen, or printing to printers without spot color support. There is no special rule for the name "All", so PDF creators must include a tint transform that converts to black in some color space, in order to maintain the same appearance as the final printed piece.

Remedies

Trapping

A remedy for slight misregistration is

trapping Animal trapping, or simply trapping or ginning, is the use of a device to remotely catch and often kill an animal. Animals may be trapped for a variety of purposes, including for meat, fur trade, fur/feathers, sport hunting, pest control, and w ...

. Trapping is a method of adjusting areas where two distinct, adjacent colors meet so that press misregistration won't cause white spaces. Where two colours abut, the lighter colour is slightly expanded into the darker to create an overlap. This yields a darker outline, which is considered less objectionable than a white gap. A major exception to this is the case when opaque (colors that completely obscure colors printed beneath them) spot colors are used. Other colors, regardless of their relative luminance, are always trapped to (spread under) these spot colors. If several of these spot colors are used (a common practice in the packaging market), the order of printing layers rather than luminance is the decisive element: the first color to be printed is spread under the next color. The trap width is dictated by the maximum amount of misregistration of the entire workflow up to the press.

Overprinting

Black ink is set to "overprint" colors in the background. The difference is not visible since the lighter color is spread underneath the—almost—opaque black.

Types of (stone) lithography registration

There are many different styles of registration for many different types of printing. These deal with stone lithography, as used in

fine arts In European academic traditions, fine art (or, fine arts) is made primarily for aesthetics or creativity, creative expression, distinguishing it from popular art, decorative art or applied art, which also either serve some practical function ...

printmaking Printmaking is the process of creating work of art, artworks by printing, normally on paper, but also on fabric, wood, metal, and other surfaces. "Traditional printmaking" normally covers only the process of creating prints using a hand proces ...

.Ross, Romano, Ross. "The Complete Printmaker", Page 226. The Free Press, 1990

T-bar

This method, using small measured registration marks on both the stone and the paper, is very accurate and simple to do. The printer measures the exact size of the paper and the desired margins. Then marks are made at both ends of the sheet of paper, and corresponding marks (usually in the shape of a "T") are made on the stone. Then the printer matches the marks on the paper to those on the stone. This way many runs of different colors can be pulled exactly in line with one another, each of them measured from the same system of marks.

Pin-hole

This method involves laying the paper on the un-inked surface, and making a pin-hole through both the bottom and top of the paper, being careful to make a mark in the stone's surface. Then the locations of the holes are transferred to each sheet of paper to be printed. When printing, one should place pins in each hole of a sheet of paper, and lower it onto the inked stone, placing each pin in its respective hole in the stone. This method can ruin paper by creating holes and if the holes get too large, they lose their function as registration devices.

Eyeballing

This method relies solely on hand–eye coordination. Eyeballing can be found in other industries as well. The printer places the paper over the stone-image, measuring and judging registration by eye. This is not very consistent, depending on the person. {, align="center" , - , , ,

References

Publishing registration Print production Quality issues in printing