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Absolute Colorimetric
A rendering intent that aims to maintain colour accuracy at the expense of preserving relationships between colours, used to predict how images will appear when printed on a paper or other substrate with a distinct colour cast, such as newsprint. With absolute colour metric rendering intent, colours that fall inside the destination gamut remain unchanged, while out-of-gamut colours are clipped. Colours are not scaled to the destination white point.

Achromatic
Perceived as having no hue; white, black or grey.

ASCII / American Standard Code for Information Interchange
This is a standard coding system used within the computer industry to convert keyboard input into digital information. It covers all of the printable characters in normal use and control characters such as carriage return and line feed. The full table contains 127 elements Variations and extensions of the basic code are to be found in special applications.

Banding
A loss of image quality in which continuous tones or gradients are broken into discrete colours or shades of grey because an image or output device does not contain or support enough tonal levels. Also known as posterization.

Bandwidth
The data transmission capacity of a system.

Bit
A binary digit; a zero or one.

Bitmap
An image arranged according to bit location in columns. Resolution of a Postscript file processed through a RIP will have a bitmapped image with the characteristics and resolution of the particular device - e.g. - laser printer from 300dpi up to 1800dpi, imagesetters or platesetters from 1200dpi up to 5080dpi.

Byte
Eight bits.

Colour calibration
Colour calibration is the process whereby a series of graphics input and output devices are calibrated, or matched, using colour profiles, in an effort to match the appearance of colour across the range of the design, pre-press and printing process. Both input devices, such as scanners and digital cameras; and output devices, such as monitors, printers, proofing devices and imagesetters, are calibrated. This is to ensure consistency throughout the publishing process. Many hardware suppliers provide a colour profile with their products, so that designers and pre-press professionals have a starting point to work from.

Calibration
The process of altering the behaviour of an input or output device to make it conform to an established state, specified by a manufacturer, user, or industrywide specification or standard.

Choke
Choking is a type of trap that involves reducing he size of a graphic colour to trap the inner colour, resulting in a hairline trap.

Colour bar
A series of coloured shapes printed outside of the finished area. These bars are used to verify the accuracy of the printing job and allows the press operator to calibrate the print job and adjust the press if necessary.

ColorSync
Apple's colour management system (CMS). ColorSync uses a variety of profiles for different input and output devices, to try and calibrate the whole design, publishing and printing process.

Colour separation
The process whereby the four (CMYK) process printing colours are separated into their primary colours to allow for professional printing.

CMYK
Cyan, Magenta, Yellow and Black (CMYK) are the four primary printing inks that make up any full colour printing job. Also known as the four process colours.

Density range
The difference between the lightest and darkest areas of an image. Also known as tonal range.

Digital proofing
Digital proofs are produced directly from an output device, as the result of a computer file - as opposed to a photo-mechanical proof.

Drum scanner
An extremely high resolution and pre-press scanner quality, that uses a high-speed rotating glass drum to scan transparencies and photographic images. Drum scanners give a much more detailed reproduction of an original than flat-bed desktop scanners and can capture a much greater range of tones. However, the gap between some of the top flatbed scanners and drum scanners is narrowing at a dramatic rate.

Electronic publishing
All encompassing term that applies to everything from digital printing techniques, to photocopied or fax machine publishing, to email publishing.

Fake duotone
Also know as false duotone, duograph, duplex halftone, screen halftone and flat tint halftone. A dummy duotone simply has the image from one plate duplicated and overprinted over the other colour plate.

Flatbed scanner
A desktop or design studio-based scanner that works by placing original artwork face down on a glass sheet and an electronic sensor scans the selected image area and outputs the digital file to a desktop computer.

Fully Formatted Disk
A disk containing all of the print-ready files required for a job to be outputted at pre-press. This could typically include the DTP document itself (e.g. a QuarkXpress or InDesign file) all the EPS logos and high resolution PhotoShop bitmap files and scans.

Gamut
The range of colours available to a specific output device, such as a laserprinter or an imagesetter. If the colour range is too wide for that particular device, it is referred to as 'out of gamut'. For example, the RGB colour range is much broader than the CMYK colour gamut (which is what most pre-press output devices use). Colours specified using the RGB gamut will often fall out of the gamut range when output on a CMYK device.

Grey Component Replacement (GCR)
Commonly known as GCR, this process involves replacing the grey tone in the cyan, magenta and yellow plates, with black ink, during the colour separation process. Not to be confused with Undercolor Removal.

Grey balance
Using cyan, magenta, yellow and black to produce a neutral grey image.

Grams per Square Metre (GSM)
GSM is the term used for the method of measuring paper and board weight.

Hexachrome
The Hexachrome printing process uses a a colour model based on six primary colours as opposed to the traditional four colour process. As well as cyan, magenta, yellow and black, Hexachrome also adds orange and green into the range. To utilise the six colours, images must be scanned and imported using software that can understand the file formats, which most up to date DTP graphics software can.

Orange and green are the hardest colours to reproduce in vibrant shades using the traditional CMYK four colour process and so Hexachrome is used when an extremely high print quality colour reproduction is required. The downside is that it is generally far more expensive at the pre-press and print production stages.

Histogram
An electronic tool in PhotoShop and other image editors, that shows the relative distribution of the density of pixels in a scan. It is used to gauge the evenness of distribution of shadow and highlight tones in scanned digital images.

Imposition
The arrangement of document pages so that they will appear in the correct order after the document has been printed and folded.

Interpolation
An interpolated bitmap image is one where pixels have been artificially added either by the input device, such as a digital camera or during in the scanning process, or afterwards in graphics editor such as PhotoShop. This is done to artificially enhance the resolution of an image.

Interpolating an image's resolution generally results in a 'soft' or fuzzy image, as the software has added pixels by 'guessing' where they should go, based on the shades of the pixels in proximity.

Knockout
Knockout is a trapping related term. It refers to the process where two colours print exactly next to each other, without overlap - hence no trapping has been applied.

The danger with object knocking out is misregister, which allows white space to show between the objects.

Lab colour
Lab is a colour system that was developed as a method of calculating all the colours that are viewable by the human eye. Lab colour is a mathematical model defined in terms of luminosity and brightness, as well as two axes - green to magenta and blue to yellows.

The Lab colour model incorporates all the colours in the CMYK spectrum and the RGB colour spectrum and is often used as an intermediary when converting one format to the other in an image editor, such as Adobe PhotoShop.

LZW compression
LZW is a compression format that is used to compress certain types of bitmap graphics images (such as TIFFs). Unlike JPEG compression, LZW is a lossless compression format - I.E. file size is reduced without the loss of image quality. The downside of compressing image with LZW is that they take longer to print.

Line screen (LPI)
Also referred to as the line screen frequency, this refers to the measure of distance between the rows of dots that make up a halftone screen. Lower line screens are used on rougher, low quality printing substrates (such as newsprint), whilst higher line screens are used for high quality print jobs on smooth art papers.

Mid-tones
Midtones are the areas in a graphic which will print closest to 50% tint, but in practice this is any shade between 30% and 70%.

Moire patterns
A moire pattern will occur in the printing process when two, or more, repeating patterns overlap each other. Similar to the effect on television when a presenter wears a criss-cross pattern on their suit, this effect will result in halftone areas of the print if the line screens of two different inks have been output at the same angle. Therefore, it is important that the screen angles of each printing plate are different.

Moire patterns can also occur when a halftone image is scanned and printed, as the dot pattern from the printed halftone can clash with the new line screen. There are numerous ways to reduce this, from blurring the scan slightly, to reducing the size of the scan, to various PhotoShop techniques and filters.

Newton's rings
Newton's rings is a flaw that can occur in a photograph or transparency that had grease on it whilst it was being scanned. The visual effect is similar to that of oil poured on water.

Open Pre-press Interface (OPI)
A graphics management system whereby a high-resolution scanned image is placed on a server and a low-resolution version is supplied to the designers for use in visual page layout only. When it is time to run the finished job for print - or high-resolution proof - the job can be output at a high resolution and the OPI files will be picked up and sent to the imagesetter.

This is especially useful because it saves time in the design studio, as it is not necessary to spend time scanning low-resolution positionals. And it also ensures that, when the final high-resolution scan is output, it will be positioned and cropped exactly as the designer intended - no need for rescanning or manual placement.

Optical resolution
The optical graphics resolution is the real maximum resolution that an input device, such as a scanner or digital camera, can render a bitmap image. As opposed to the interpolated resolution.

Pantone
The proprietary Pantone colour matching system is the most popular method of specifying extra colours - not out of the CMYK four colour process - for print. Pantone colours are numbered and are made up out of a base set of colours. By specifying a specific Pantone colour, a designer knows that there is little chance of colour variance on the presses.

Pantones are generally used as spot colours, such as logos, to ensure colour consistency for corporate identities. However, they can also be used in halftone graphics and for duotones.

Pantones can also be simulated using the colours from the CMYK spectrum - and Pantone even publish a guide for doing so. However, the results can often be unsatisfactory, especially for greens and oranges. This is one of the motivations for the development of the Hexachrome printing system.

Platesetter
A plate-setter is a type of imagesetter that outputs press-ready digital files directly onto printing plates, as opposed to films.

Press proof
A press proof is a a printed proof that has been run using an actual printing press and commercial printing inks. This is generally done immediately prior to running the actual job.

Proofing press
There are special proofing presses which are built with the specific purpose of creating accurate proofs. The advantage is that the proofs are printed using the same materials - ink and paper - as the intended print job, without the commercial commitment of the press proof. The downside is that the colours are often more vibrant than they would be on the actual printed document.

Quadtone
A quadtone is, in principle, the same as a duotone, but involving four inks instead of two.

Quartertone
The printed part of an image where the grey value is either 25% or 75%.

Raster image processor (RIP)
A RIP is a hardware or software tool that processes a digital PostScript file and converts it - rasterises - to a printable format.

Reflective
The opposite of a transparency or transmissive, in that it reflects light. A photograph is a typical reflective artwork.

Resolution
For the sake of graphics reproduction, the resolution of a bitmap digital graphics image is a measure of its quality, or the amount of digital information it contains. Resolution is measured by the amount of pixels an image contains in height and width. For professional printed reproduction, the resolution of a bitmap graphics file must be between 1.5 and 2.5 times the resolution of the line screen.

Rich black
Because of impurities in commercial printing inks 100% solid black generally appears nearer to a dark grey. Because of this, printers often add a 'wash' of other coloured inks to create a rich black. Typically this is 40% of cyan, but other combinations of cyan, yellow, magenta and black are not unknown.

Server
A computer which has been set up specifically to store and 'serve' files to other computer users. In a design studio or prepress environment, this is essential to prevent the duplication of files and so that an effective backup policy can be implemented.

Spread
As regards colour reproduction, a spread is a trapping reference. A spread is created when the inner, or lighter, graphic is set to spread out to overlap an outer, darker, object to create the trap.

Trapping
Because the commercial printing process involves laying down colours in sequence , as opposed to, for example, laser printing, it is nearly impossible to align every graphic object exactly.

Because of this, objects of different colours, that are next to each other, are set to trap. What this means in practice is that one object overlaps the other by a fraction of a millimetre, thereby ensuring that there is no white space in-between them.

Tritron
Identical process to a duotone or quadtone, but with three printing inks, as opposed to two or four.

Undercolor Removal (UCR)
Reducing the amount of cyan, magenta and yellow ink in the midtones and shadow areas of an image, whilst the amount of black ink is increased. Commonly referred to as UCR.

Viewing booth
A viewing booth is an area, or even entire room, that has been specially set up with balanced lighting conditions, for viewing proofs and printed artwork.

White point
The lightest area of a computer monitor is called the white point. This refers to the colour temperature of the monitor and generally varies from 5000 Kelvins, to 6500K, through to 9300K.

XML / eXtensible Metadata Language
eXtensible Metadata Language, the standard way of encoding metadata to enable application interoperability and automation.



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