Stripping (printing)

Last updated

Within the commercial printing industry, the job of stripping involves arranging and joining film negatives as part of the process of preparing printing plates. [1] In the UK, the same operation is termed "planning" and film positives are used, rather than the negatives in the USA. Because the industry has largely moved to digital processes, the job of stripping, or planning has become rare or even obsolete.

Contents

Negatives may be set up in a pattern to allow a printing press to print 4, 8, 16 or 32 pages at a time, front and back, which are then folded to produce a brochure or book with the correct pagination (see figure). Conversely, a variety of smaller printed products of various sizes may be arranged on a single larger press sheet to be cut down after printing into individual job components, such as business or post cards, folding boxes or hang tags.

Color and density

For color processes, an individual black and white, "screened" negative is used to represent each color in a four-colour process (Cyan, Magenta, Yellow and Black) to be printed on a printing press. A screened negative has varying sizes of dots arranged in a particular pattern to represent greater or lesser density of image. Typically, a 150 dots-per-inch screen is used to create each printing negative, though this will varying depending on the application, where a magazine may use 200 line screens and a newspaper may use 120 to 133 line screen. The screen is rotated at successively varied angles to ensure that the dots do not print exactly on top of one another.

"Cleaning" a negative of unwanted artifacts (noise) from the line camera process, (lines, etc., from the edges of traditional hot-wax analog "font" paste-up, and dirt), would be done by scraping the exposed emulsion from the negative with an X-Acto Knife (for areas intended to be exposed on the printing plate). Similarly, negatives were "opaqued" with an opaquing solution applied with a brush, or felt-tipped pen, or (opaque) red adhesive tape (for larger areas), to prevent exposure of white specs, noise, etc., especially on large fonts.

Alignment

Each negative must be precisely aligned and secured by tape to a light-blocking paper or plastic mask. The painstaking alignment of the negatives requires a stripper to use high-magnification eye piece while viewing the work on top of a light table to achieve exact positioning. Once secured, the area of the mask through which light must pass is removed with an Exacto knife or razor blade.

Exposure and developing

The completed mask with opened exposure windows is then placed atop a photo-sensitive printing plate, which both plate and mask with stripped negatives fixed by register pins, and then vacuum-sealed in a framed enclosure under glass and exposed to very bright light, allowing the rays to pass through the negatives and expose the printing plate's surface. The plate is then developed and the unexposed areas are washed away, leaving behind cured emulsion that will hold the ink on press. A single etched plate is necessary for each color to be printed.

Diagram

8up imposition.svg

Digital prepress

The process of stripping for general commercial offset printing has largely been eliminated through the use of digital prepress technology, in which imposition software is used to "digitally strip" the pages together. Some printing technologies continue to use stripped film, especially in silk-screen printing, although this is likely to change in the near-term. The digital product of this imposition software can be outputted to an imagesetter that creates a single, composed piece of film, or directly to a platesetter which generates a plate that can go directly to press.

Related Research Articles

<span class="mw-page-title-main">Lithography</span> Printing technique

Lithography is a planographic method of printing originally based on the immiscibility of oil and water. The printing is from a stone or a metal plate with a smooth surface. It was invented in 1796 by the German author and actor Alois Senefelder and was initially used mostly for musical scores and maps. Lithography can be used to print text or images onto paper or other suitable material. A lithograph is something printed by lithography, but this term is only used for fine art prints and some other, mostly older, types of printed matter, not for those made by modern commercial lithography.

<span class="mw-page-title-main">Color photography</span> Photography that reproduces colours

Color photography is photography that uses media capable of capturing and reproducing colors. By contrast, black-and-white or gray-monochrome photography records only a single channel of luminance (brightness) and uses media capable only of showing shades of gray.

Prepress is the term used in the printing and publishing industries for the processes and procedures that occur between the creation of a print layout and the final printing. The prepress process includes the preparation of artwork for press, media selection, proofing, quality control checks and the production of printing plates if required. The artwork is quite often provided by the customer as a print-ready PDF file created in desktop publishing.

<span class="mw-page-title-main">Offset printing</span> Printing technique

Offset printing is a common printing technique in which the inked image is transferred from a plate to a rubber blanket and then to the printing surface. When used in combination with the lithographic process, which is based on the repulsion of oil and water, the offset technique employs a flat (planographic) image carrier. Ink rollers transfer ink to the image areas of the image carrier, while a water roller applies a water-based film to the non-image areas.

<span class="mw-page-title-main">Enlarger</span> Specialized transparency projector

An enlarger is a specialized transparency projector used to produce photographic prints from film or glass negatives, or from transparencies.

<span class="mw-page-title-main">Contact print</span> Photographic image produced directly from film

A contact print is a photographic image produced from film; sometimes from a film negative, and sometimes from a film positive or paper negative. In a darkroom an exposed and developed piece of film or photographic paper is placed emulsion side down, in contact with a piece of photographic paper, light is briefly shone through the negative or paper and then the paper is developed to reveal the final print.

<span class="mw-page-title-main">Photogravure</span> Photographic printing technique

Photogravure is a process for printing photographs, also sometimes used for reproductive intaglio printmaking. It is a photo-mechanical process whereby a copper plate is grained and then coated with a light-sensitive gelatin tissue which had been exposed to a film positive, and then etched, resulting in a high quality intaglio plate that can reproduce detailed continuous tones of a photograph.

Imposition is one of the fundamental steps in the prepress printing process. It consists of the arrangement of the printed product's pages on the printer's sheet, in order to obtain faster printing, simplify binding and reduce paper waste.

C-41 is a chromogenic color print film developing process introduced by Kodak in 1972, superseding the C-22 process. C-41, also known as CN-16 by Fuji, CNK-4 by Konica, and AP-70 by AGFA, is the most popular film process in use, with most, if not all photofinishing labs devoting at least one machine to this development process.

Color printing or colour printing is the reproduction of an image or text in color.

<span class="mw-page-title-main">Compositing</span> Combining of visual elements from separate sources into single images

Compositing is the process or technique of combining visual elements from separate sources into single images, often to create the illusion that all those elements are parts of the same scene. Live-action shooting for compositing is variously called "chroma key", "blue screen", "green screen" and other names. Today, most compositing is achieved through digital image manipulation. Pre-digital compositing techniques, however, go back as far as the trick films of Georges Méliès in the late 19th century, and some are still in use.

<span class="mw-page-title-main">Computer to plate</span> Imaging technology used in printing

Computer-to-plate (CTP) is an imaging technology used in modern printing processes. In this technology, an image created in a desktop publishing (DTP) application is output directly to a printing plate.

<span class="mw-page-title-main">Bipack</span> Cinematography visual effect process

In cinematography, bipacking, or a bipack, is the process of loading two reels of film into a camera, so that they both pass through the camera gate together. It was used both for in-camera effects and as an early subtractive colour process.

<span class="mw-page-title-main">Color motion picture film</span> Photographic film type

Color motion picture film refers both to unexposed color photographic film in a format suitable for use in a motion picture camera, and to finished motion picture film, ready for use in a projector, which bears images in color.

Camera-ready is a common term used in the commercial printing industry meaning that a document is, from a technical standpoint, ready to "go to press", or be printed.

Dye transfer is a continuous-tone color photographic printing process. It was used to print Technicolor films, as well as to produce paper colour prints used in advertising, or large transparencies for display.

In bipack color photography for motion pictures, two strips of black-and-white 35 mm film, running through the camera emulsion to emulsion, are used to record two regions of the color spectrum, for the purpose of ultimately printing the images, in complementary colors, superimposed on one strip of film. The result is a multicolored projection print that reproduces a useful but limited range of color by the subtractive color method. Bipack processes became commercially practical in the early 1910s when Kodak introduced duplitized film print stock, which facilitated making two-color prints.

<span class="mw-page-title-main">Photographic film</span> Film used by film (analog) cameras

Photographic film is a strip or sheet of transparent film base coated on one side with a gelatin emulsion containing microscopically small light-sensitive silver halide crystals. The sizes and other characteristics of the crystals determine the sensitivity, contrast, and resolution of the film. Film is typically segmented in frames, that give rise to separate photographs.

<span class="mw-page-title-main">Technicolor</span> Color motion picture process

Technicolor is a series of color motion picture processes, the first version dating back to 1916, and followed by improved versions over several decades.

A contact copier is a device used to copy an image by illuminating a film negative with the image in direct contact with a photosensitive surface. The more common processes are negative, where clear areas in the original produce an opaque or hardened photosensitive surface, but positive processes are available. The light source is usually an actinic bulb internal or external to the device

References

  1. "How Offset Printing Works". HowStuffWorks. 2001-03-02. Retrieved 2024-06-05.