Scannerguide

 

8 24 32 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

8-bit grayscale
Images that contain 256 possible shades of gray.

24-bit color
24-bit color images are composed of three 8-bit color channels. Each color channel, similar to an 8-bit grayscale image, contains up to 256 colors. When combined, the red, green and blue channels provide up to 16.7 million colors. 24-bit color is also known as True Color and Photo-realistic Color.

32-bit color
32-bit color images have 4 color channels of 8 bits each - one channel each for red, green and blue, plus 8 bits of grayscale data to provide higher detail.

A/D converter
A device used to convert analog data to digital data. Analog data is continuously variable, while digital data contains discrete steps.

additive primaries
Red, green, and blue light that, together, produce white light. These are the primary colors of light from which all other colors can be made. Compare with subtractive primaries.

aliasing
Visibly jagged steps along angled lines or object edges, due to sharp tonal contrasts between pixels.

alpha channel
An 8-bit channel reserved by some image-processing applications for masking or additional color information.

analog
Continuously variable signals or data. Description of the continuous wave or signal (such as the human voice) using an electrical voltage variation. Used for voice, visual, and computer data communication. The digital or pulse output of a computer or terminal must be converted to an analog signal before it can be transmitted over analog grade lines.

anamorphic sizing
Unequal scale change in the horizontal and vertical direction of a scanner. This enables the scanner to adjust the ratio in the horizontal and vertical direction.

anti-aliasing
The rendering of hard-edged objects so they blend smoothly into the background. A technique for merging object-oriented art into bitmaps.

array
An ordered collection of elements of the same type. Represented by single line of sensors in a CCD chip are called a linear array. A digital image is stored as a 2-dimensional data array containing pixels addressable by x,y (or row, column) coordinates.

artifact
A visible indication (defect) in an image, caused by limitations in the reproduction process.

ASCII (American Standard Code for Information Interchange)
Standard by which many computers assign code numbers to letters, numbers and symbols. Used for text exchange between computer platforms.

banding
A visible stair-stepping of shades in a gradient.

batch scanning
Sequential scanning of multiple originals using previously-defined, unique settings for each.

Bezier curves
In object-oriented programs, a curve whose shape is defined by anchor points set along its arc.

bilevel
A type of image containing only black and white pixels.

binary
Binary, or base 2, is a numbering system with only two digits, 0 and 1. Binary is convenient for use with bits which have only two states, on and off.

bit
The smallest unit of memory in the computer. A bit can be either off or on, representing a value of 0 or 1. Bits can be used in combination to represent higher numbers.

bit depth
The number or bits used to represent each pixel in an image, determining its color or tonal range

bitmap
An image formed by rectangular grid of picture elements (pixels). The computer assigns a value to each pixel, from one bit of information (indicating black or white) to 24 bits per pixel (for full-color computer displays), to as many as 64 bits per pixel for some types of full-color images. A bitmap is an image defined by a collection of dots, as opposed to a vector image, which is defined by mathematical formulas.

black & white
Refers to both line art and halftone bitmapped image types.

black point
A movable reference point that defines the darkest area in an image, causing all other areas to be adjusted accordingly.

brightness
The intensity of a color or tone regardless of its hue or saturation.

byte
A unit of measure equal to eight bits of digital information. The standard unit measure of file size. See also megabyte, kilobyte, and gigabyte.

calibration
Setting equipment to a standard measure to produce reliable results.

calibration bars
On a negative, proof or printed piece, a strip of tones used to check printing quality.

camera ready
Copy assembled and suitable for photographing by a process camera with minimum number of steps.

camera-ready art
Any artwork or type that is ready to be prepared for printing.

CCD
A charge-coupled device, or CCD, is a light sensitive electronic device that converts light into an electrical charge.

CCD (Charge Coupled Device)
A diode that is light-sensitive when charged with electrical voltage.

Chromalin
An off-press color proofing system developed by DuPont. The proofs are single laminated sheets produced from film separations.

CIE (Commission Internationale de l'Eclairage)
An international group that has developed a set of color definition standards endorsed by Adobe for PostScript Level 2.

clipping (sense 1)
Process of setting graphics display boundaries. The clipping volume is defined by the window, near and far clipping planes, and projectors of the corners of the window. Data on the planes forming the edges are considered to be within the volume. (2) The conversion of all tones lighter than a specified gray level to white, or darker than a specified gray level to black, causing loss of detail. This also applies to individual channels in a color image.

CMS
Color management system. This ensures color uniformity across input and output devices so that final printed results match originals. The characteristics or profiles of devices are normally established by reference to standard 1T8 color targets.

CMYK (Cyan, Magenta, Yellow, Black)
The subtractive primaries, or process colors, used in color printing. Black (K) is usually added to enhance color and to print a true black.

color cast
An overall color imbalance in an image, as if viewed through a colored filter.

color channel
Color images on the computer are created by combining different color channels. In RGB, the most commonly used color model, the channels are red, green and blue.

color correction
The process of adjusting an image to compensate for scanner deficiencies or for the characteristics of the output device.

color picker
A utility for specifying colors on the monitor.

color proof
A representation of what the final printed composition will look like. The resolution and quality of different types of color proofs can vary greatly.

color separation
Output or electronic files that contain image information for only one printing ink.

color separation
The division of an image into its component colors for printing. Each color separation is a piece of negative or positive film.

color space
Three-dimensional model (or representation of a 30 model) used to organize colors to show progressions of hue, lightness, and saturation. Device-independent color spaces are based on international standards (CIE).

color transparency
A photographic image on transparent film used as artwork. 35mm, 4"x5" and 8"x 1O" formats are commonly used.

colorimeter
A light-sensitive device for measuring colors by filtering their red, green and blue components, as in the human eye. See also spectrophoto-meter.

comp
Comprehensive artwork used to present the general color and layout of a page. See proof.

compression
Encoding the bits of information in an image file so that it takes up less space when stored. Compression results in little or no distortion.

compression
The reduction in size of an image file. See also lossy and non-lossy.

continuous-tone
Image that has a complete range of tones from black to white: photographs, paintings and drawings. Negative or positive with a broad range of tones that have no screened dots.

contone (CT)
An abbreviation for continuous tone. A color or grayscale image format capable of illustrating continuously varying tonal ranges, as opposed to line art. CT is also the name of a file format used for exchanging high-level scan information.

contrast
The relationship between the light and dark areas of an image. The more extreme the difference, the greater the contrast.

crop marks
Lines printed showing the dimensions of the final printed page. These marks are used for final trimming.

data compression
"Squeezing" of data for the purpose of transmission throughput or storage efficiency. Portions of the data are removed using an algorithm that will restore the data when needed.

DCS
Desktop color separation. An image format consisting of four separate CMYK PostScript files at full-resolution, together with a fifth EPS master for placement in documents.

decompression
The expansion of compressed image files. See also lossy and non-lossy.

default
Command or parameter that takes effect if no other option is specified.

densitometer
A measuring instrument that registers the density of transparent or reflective materials. It is used to check the accuracy, quality, and consistency of output. Colors are read as tonal information. See also colorimeter and spedrophotometer.

density
The ability of a material to absorb light. Measure of the light transmission of a transparent or translucent object or the light-absorbency of a reflective surface. In photography, measurement of the opacity of a transparent or translucent object. On a film negative, the greater the density area, the more black or more developed it is. Density is measured from 0 to 4.0. It is calculated by measuring the reflectance or transmittance of light and calculating theoretical light absorption.

descreening
Removal of halftone dot patterns during or after scanning printed matter by defocusing the image. This avoids moire patterning and color shifts during subsequent halftone reprinting.

dichroic mirror
A special type of interference filter, which reflects a specific part of the spectrum, whilst transmitting the rest. Used in scanners to split a beam of light into RGB components.

digital
Method of data storage and/or transmission wherein each element of information is given a unique combination of numerical values (bits). Each bit indicates either the presence or absence of a condition (such as on-off, yes-no, true-false, open-closed). Digital data or voltages consists of discrete steps or levels, as opposed to continuously variable analog data.

Digital-to-Analog Conversion (D/A)
Conversion of digital information into a state of fluctuating voltage levels. (DAC) Interface to convert digital data (represented in discrete, discontinuous form) into analog data (represented in continuous form).

direct-digital color proof
A proof made from a stored data file onto a substrate without producing intermediate separation film.

direct-to-plate
Direct exposure of image data onto printing plates, without the intermediate use of film.

direct-to-press
Elimination of intermediate film and printing plates by the direct transfer of image data to printing cylinders in the press.

display
Temporary visual representation of computer output on a CRT or other electronic device.

dithering
The process of specifying color to adjacent pixels in order simulate a third color in a bitmapped image. This technique is used when a full range of colors is not available.

Dmax
The highest level of density of a film positive or negative.

Dmin
The point of minimum density in an image or original.

dot
Smallest visible point that can be displayed on a display surface.

dot gain
A printing defect in which dots print larger than intended, causing darker colors or tones. Dot gain measures the increase in halftone dot values that occur during the offset printing production process. Total dot gain is measured as the difference in apparent dot size between the final printed product and the original film. Dot gain occurs as the result of both mechanical and optical influences on the original dot size.

dots, halftone
Minute, symmetrical individual subdivisions of the printing surface formed by a half-tone screen.

down-sampling
The reduction in resolution of an image, necessitating a loss in detail.

DPI (Dots-Per-Inch)
A method of denoting the resolution of a scanned image, a digitized image in a file, or an image as rendered by an output device. Also, used interchangeably with pixels per inch (PPI).

drum scanner
An optical input device that mounts reflective or transparent input media on a revolving cylinder for digitizing.

dye sublimation
A printing process using small heating elements to evaporate pigments from a carrier film, depositing these smoothly onto a substrate.

elliptical dot
A type of halftone screen dot with an elliptical rather than circular shape, which sometimes produces better tonal gradations.

emulsion
The coating of light-sensitive material on a piece of film.

emulsion down
This specifies a readable film image with the emulsion side facing away from the viewer. The printer usually decides whether emulsion should be up or down.

EPS (Encapsulated PostScript)
This format carries a pict preview and is the only format that supports saving line screen data and transfer functions. In bitmapped mode, it also supports transparent whites.

EPS 5
Another term used for DCS.

export
To output data in a form that another program can read.

file
A named collection of information stored as an apparent unit on a secondary storage medium such as a disk drive.

film
Photosensitive material, generally on a transparent base, which will receive character images, and may be chemically processed to expose those images. In imagesetting, any photosensitive material, transparent or not, may be called film.

film negative
A piece of film with a reversed image, in which dark areas appear white, and vice versa.

film recorder
Used in reference to color transparency recording devices, and sometimes also to imagesetters.

flatbed scanner
Any scanning device that incorporates a flat transparent plate, on which original images are placed for scanning. The scanning process is linear rather than rotational.

four-color process
The use of cyan, magenta, yellow, and black in printing to produce a wide variety of colors.

FPO (For Position Only)
A low resolution image placed in a document to indicate where the final version is to be positioned.

frame-grabbing system
A combination of hardware and software, designed to capture individual frames from video clips for further digital manipulation, or consecutive replay on computer platforms.

Gamma
A mathematical function used to describe the relationship between input densities (levels) and output densities (levels.) The measure of how compressed or expanded dark or light shades become in an image.

gamma correction
The correction of tonal ranges in an image, normally by the adjustment of tone curves.

gamut
The limited range of colors provided by a specific input device, output device, or pigment set.

gang scanning
Sequential scanning of multiple originals using the same previously-defined exposure setting for each.

GCR (Gray Component Replacement)
A technique for reducing the amount of cyan, magenta and yellow in an area and replacing them with an appropriate level of black.

gigabyte
A unit of measure of stored data corresponding to one billion bytes of information.

gigabyte (Gb)
1,024 megabytes, or 1,048,576 kilobytes of digital data.

gradation
A smooth transition between black and white, one color and another, or color and the lack of it.

gradation (contrast)
A relationship of the distribution of tone values in the reproduction to the original.

gray balance
The balance between CMY colorants required to produce neutral grays without a color cast.

gray levels
Discrete tonal steps in a continuous tone image, inherent to digital data. Most CT images will contain 256 gray levels per color.

grayscale
(1) An image type consisting of shades of gray, with no color. The standard grayscale image contains 8 bits per pixel, which allows for 256 shades. (2) The depiction of gray tones between black and white. A grayscale monitor is able to display distinct gray pixels as well as black and white ones, but not color pixels. (3) An orderly variable progression in definite steps of gray densities ranging from minimum zero (white) to maximum density (black). A strip of standard gray tones placed at the side of the original copy during a photography to measure tonal range obtained. Used in processing film or materials such as photographic paper and plates.

halftone
An simulation of continuous tones by the use of black or overlapping process color dots of varying size or position.

halftone screen
A pattern of dots of different sizes used to simulate a continuous tone photograph, either in color or black and white.

halftoning factor
See quality factor.

halo
A light line around object edges in an image, produced by the USM (sharpening) technique.

hard dot
A dot in a halftone screen that has smooth, crisp edges.

high contrast
Reproduction technique in photography with high gamma in which the difference in darkness (density) between neighboring areas is greater than in the original.

high key
A very light original image (possibly overexposed) that contains important detail in the highlight area.

highlight
The lightest or whitest part of an image with discernible detail. A highlight is represented in a halftone image by the smallest dot patterns. A specular highlight is whiter and lighter, but has no detail.

histogram
A graphic representation of the number of pixels with given color values, Showing the breakdown or distribution of color values in a picture.

HLS
A color model based on three co-ordinates: hue, lightness (or luminance) and saturation.

HSV
A color model based on three co-ordinates: hue, saturation and value.

hue
The wavelength of light of a color in its purest state (without the addition of white or black).

imagesetter
An output device used to render high resolution images or documents on photographic paper or film.

input
Raw data, text, graphics, imagery or commands inserted into a computer.

interpolation
The process of increasing the resolution of an image by the addition of new pixels throughout the image, the colors of which are based on neighboring pixels.

JPEG (Joint Photographic Expert Group)
An image compression/decompression standard that divides the image area into cells to condense information based on content analysis.

K
(1) Abbreviation for the color black. K is used so that it is not confused with an abbreviation for the color blue. (2) Represents "kilobytes" of information which is 1024 bits. The K is upper-case to distinguish it from lower-case k, which is a Standard International Unit for "kilo", or 1,000.

kernel size
The number of pixels sampled as a unit during image manipulation and sharpening processes.

kilobyte
(K, KB) A unit of measure of digital information corresponding to 1024 bytes. Abbreviated and referred to as K.

kilobyte (Kb)
1,024 bytes of digital data.

knockout
A shape or object printed by eliminating (knocking out) all background colors. Contrast to overprinting.

LAN
Local Area Network. A group of connected computers in a relatively small area that share access to printers and other peripheral devices.

laser printer
Computer output device that uses a laser to generate the character images. It uses some of the same methods to produce the final image as a copier.

line art
Images containing only black and white pixels. Also known as bilevel images. The term line art is sometimes used to describe drawings containing flat colors without tonal variation, that is, a single-bit image type that lacks any dithering effect.

lossless
Data compression algorithms that store data in a more efficient format that does not cause any data loss in the compression process. Typically this type of compression has a ratio of up to 8:1.

lossy
Data compression algorithms that assumes some of the data in an image file is unnecessary and can be eliminated without affecting the perceived image quality. Typically this type of compression has ratios between 10:1 and 100:1.

low key
A dark image (possibly underexposed) that contains important detail in the shadow area.

LPI
Lines Per Inch. A measure of the frequency of a halftone screen (usually ranging from 55-200). Originally, halftones were made by placing an etched glass plate over an image and exposing it to produce dots. Lpi refers to the density of the horizontal and vertical lines.

luminosity
A value corresponding to the brightness of color.

LUT
Look-Up Table. The table of colors a computer can display at a given time. The computer uses the table to approximate the desired color from the range it has available.

LZW
The Lempel-Ziv-Welch image compression technique.

MacPaint
A common format on the Macintosh computer for storing and transferring low-resolution, monochromatic bit-mapped images. It originated with the paint application of the same name.

mask
The inactive area of a bitmapped image which will not respond to changes.

matrix
This often refers to a 2-dimensional array of CCD elements.

megabyte (Mb)
1,024 kilobytes or 1,048,576 bytes of digital data.

memory
A device into which data can be entered, in which if can be held, and from which is can be retrieved at a later time. Data is stored in digitally encoded bits, and manipulated as needed during calculation processes. The amount of memory a computer has directly affects its ability to perform complex functions.

midtones
Tonal values located between highlights and shadows. Midtone definition controls the contrast in image reproduction by determining the separation of tones in the image.

moiré
Undesirable screen pattern in color process printing caused by incorrect screen angles of halftones.

monitor
Electronic display unit that uses cathode ray tube to generate text, graphics and imagery. It looks like a normal TV set, however, the monitor has a much higher degree of resolution.

monitor calibration
The process of optimizing the color settings of a monitor to match selected colors of a printed output.

monochrome
Single-colored. An image or medium displaying only black-and-white or grayscale information, Grayscale information displayed in one color is also monochrome.

mottling
A texture similar to orange peel sometimes caused by sharpening. It is particularly visible in flat areas such as sky or skin.

negative
See film negative.

neutral gray
Any level of optical density (from white to black) having no apparent hue. It consists of equal levels of red, green, and blue (RGB).

noise
In the scanning context, this refers to random, incorrectly read pixel values, normally due to electrical interference or device instability.

non-lossy
Image compression without loss of quality.

object-oriented
A type of drawing that defines an image mathematically rather than as pixels in a bitmap.

OCR (Optical Character Recognition)
The analysis of scanned data to recognize characters so that these can be converted into editable text.

off-press proof
A color proof generated prior to the production press run and prior to, or in lieu of, a press proof.

offset lithography
A high-volume, ink-based printing process, in which ink adhering to image areas of a lithographic plate is transferred (offset) to a blanket cylinder before being applied to paper or other substrate.

optical resolution
In the scanning context, this refers to the number of truly separate readings taken from an original within a given distance, as opposed to the subsequent increase in resolution (but not detail) created by software interpolation.

original
A term used for any artwork or photograph that is scanned.

output
Process of sending computer results to a CRT or printer.

overprinting
Printing over areas already printed. Contrast to knockout.

PICT/PICT2
A common format for defining bitmapped or object-oriented images on the Macintosh. The more recent format (PICT2) supports 24-bit color.

pigment
Particles that absorb and reflect light and appear colored to our eyes. The substance that gives ink its color.

pixel
Another term for picture element; the smallest raster display element, represented as a point with a specified color or intensity level. A two-dimensional array of dots that define the form and color of an image. Measurement is indicated as PPI. (pixels per inch) The term pixel is usually interchangeable with dot, but pixel most often refers to screen dots rather than image dots. The eye merges differently colored pixels into continuous tones.

pixel skipping
A means of reducing image resolution by simply deleting pixels throughout the image.

PMS (Pantone Matching System)
A commonly used system for identifying specific ink colors.

PMT (Photomultiplier Tube)
A light sensitive tube that can detect very low light levels by amplifying the signals applied to it. Usually associated with drum scanners.

posterization
The conversion of continuous tone data into a series of visible tonal steps or bands. Intentional, as opposed to banding.

PostScript
The standard device-independent language developed by Adobe Systems that describes the appearance of pages in documents. PostScript describes a page in its final form, ready for imaging on an output device. Encapsulated PostScript describes a graphic, image or complete page in a final form in a way that can be exchanged between application programs so that one PostScript described item can be included in another layout.

PPI (Pixels Per Inch)
A measure of the amount of scanned information. The finer the optics of the scanner the higher the scan resolution. PPI is equivalent to DPI.

prepress
Refers to the steps required to go from original to film.

prepress proof
Proof made before the final press run by exposing the film negatives or positives to pigmented or dyed light sensitive materials. When assembled, it will be similar in appearance to the finished printed product.

prescan
A preliminary or preview scan of an original to determine the correct setup and cropping prior to full scanning.

primary color
A base color that is used to compose other colors,

printing plate
Surface, usually made of metal, that has been treated to carry an image. The plate is inked and the ink is transferred to the paper or other surfaces by a printing press. Printing plates are also made of rubber, synthetic rubber, and plastics.

process colors
The four colors (cyan, magenta, yellow and black) that are combined to print a wide range of colors. When blended, these reproduce only a small portion of all the colors found in nature, but they can reproduce the widest range with the fewest inks when printing. See also CMYK.

profile
The color characteristics of an input or output device, used by a CMS to ensure color fidelity.

proof
Working copy of some material used for review and approval. A reasonably accurate sample of how a finished piece is intended to look.

quality factor
A multiplication factor (between 1 and 2) applied to output screen ruling to calculate scanning resolution for optimum output quality. This is also known as the halftoning factor.

quarter tones
Tones between shadow and midtones are known as 314 tones and those between highlight and midtones are known as 1/4 tones.

RAM (Random Access Memory)
The memory a computer needs to store the information it is processing at any given moment. This is short-term memory and is lost when the power is shut off. RAM may be expanded by adding memory chips or memory boards.

random proof
A proof consisting of many images ganged on one substrate and positioned with no regard to final page imposition.

raster
A synonym for grid. Sometimes used to refer to the grid of addressable positions in an output device.

raster image
An image composed of a pattern of dots or pixels. Same as a bitmapped image.

rasterization
The process of converting mathematical and digital information into a series of dots by an imagesetter for the production of negative or positive film. See also RIP.

reflective art
Artwork prepared so that it may be photographed or input into a computer by scanning.

registration
The alignment of different films or printing plates to produce one printed image.

registration marks
Small cross-hairs on film used in the alignment of negatives.

REL
Recorder element. The minimum distance between two recorded points (spots) in an imagesetter.

RES
Unit of measure of resolution in number of lines per millimeter, such as RES8 or RESlOD. To convert RES to DPI, multiply the RES value by the number of millimeters in an inch, 25.4 (For example, RES12 = 300 DPI).

resampling
An increase or reduction in the number of pixels in an image, required to change its resolution without altering its size. See also down-sampling and interpolation.

resolution
The measure of image details. The smallest discernible detail in visual rendering. Resolution may be stated in terms of spot diameter, line width, pixel matrix dimension, raster lines or dots/inch.

retouching
Art of making digital, chemical, or dye corrections by adding or removing density or color, on continuous tone film, on color transparency materials or on reflection prints. Digital retouching makes changes to pixel values to enhance image appearance.

RGB (Red, Green and Blue)
The color model in which color images are composed of red, green and blue color channels. Most computer displays and image editing programs use the ROB color model.

RIP (Raster Image Processor)
Part of an output device that rasterizes, or converts mathematical and digital information into a series of dots, so that it can be rendered and imaged onto a screen, film, paper or other media.

rosette
The dot pattern created when all four color halftone screens are placed at the traditional angles.

RPI (Rels per Inch)
A measurement of the number of discrete steps that exposure units in imagesetting devices can make per inch.

sampling
The process of converting analog data into digital data by taking a series of samples or readings at equal time intervals.

saturation
The amount of gray in a color. The higher the gray content, the lower the saturation.

scale
To change the proportion of an image by increasing or decreasing its size.

scan
To examine or capture an image by means of a moving light beam. Scanning technology is used in imaging, optical character recognition, and other areas.

scanner
A device used to digitize images to be manipulated, output, or stored on a computer.

screen
To break up continuous-tone copy into dots for reproduction as a halftone. Line screens are designated by the number of ruled lines they contain: from 50 lines per inch to 500 lines per inch. The greater the number of lines per inch, the sharper and fine the printed half-tone. The selection of the screen is dictated by the paper, press, the nature of the copy.

screen angles
The angles used to offset the different films in process color separations. Proper screen angles are critical to minimize moire' patterns.

screen ruling or frequency
The number of lines per inch in the halftone screen. The lower the number, the larger and more widely spaced the dots. Higher screen rulings allow reproduction of fine detail.

SCSI (Small Computer System Interface)
An internal communications standard for computers, through which hard drives, scanners, and other peripherals transfer data.

second original
High-quality, contone reproduction of an image, intended to be identical to the original.

secondary color
Color obtained by mixing two primary colors, Although known as primary colorants, C, M and Y are the secondary colors of light. Red plus green produce yellow for example.

service bureau
A business that specializes in outputting computer files on laser imagesetters, film recorders, large-format plotters and other types of output devices.

shadow
The darkest part of an image with discernible details, represented in halftone images by the largest dot patterns.

sharpen
Electronic photo-retouching function for enhancing image detail and contrast either globally or in selected regions of the picture.

sheetfed
Type of scanning device in which the original is moved past the scanning head, rather than having the scanner head move. Usually appropriate only for sheets of paper.

single-bit images
Black and white bitmapped images, of either line art or halftone image type.

soft dot
A type of dot in a halftone screen whose edge is not smoothly circular. This can create a fuzzier image. By contrast, a hard dot has a very smooth edge.

speckling
Isolated light pixels in predominantly dark image areas, sometimes caused by incorrect readings or noise in the scanning device.

spectrophotometer
An extremely accurate color measurement device using a diffraction grating to split light into its component wavelengths, which are then measured by numerous light sensors.

specular highlight
Small reflection or detail highlight in a photograph that is reproduced in halftone form with a 0% dot value.

spot
Smallest region of an input or output image whose tone can be controlled independently of all other regions. A digitally generated halftone dot is constructed using a matrix of spots.

staircasing
See aliasing.

stripping
The preparation and assembling of film prior to platemaking.

substrate

The base material used to carry or support an image, for example paper or film.

subtractive primaries
The inks (cyan, magenta, and yellow) used in printing to create different colors. In contrast to additive primaries, these produce darker colors when combined. Another term for primary colorants.

supersampling
The capture of more gray levels per color than is required for image manipulation or output. This additional data allows shadow details to he heightened, for example.

tag
See profile.

TGA (Targa)
A file format for exchanging 24-bit color files on PCs.

thermal wax transfer
A printing process using small heating elements to melt dots of wax pigment on a carrier film, which are then transferred to paper or transparent film by contact. This differs from the dye sublimation process in that individual dots do not fuse together, so thermal wax transfer appears to be of a lower resolution.

threshold
The point at which an action begins or changes. The threshold setting used in scanning line art determines which pixels are converted to black and which will become white. The threshold defined in the USM process determines how large a tonal contrast must be before sharpening will be applied to it.

Thresholding
The process of rendering all areas darker than a certain value as black, and all lighter areas as white. Used to convert grayscale images to black and white.

TIFF (Tagged Image File Format)
A file format developed by Aldus Corporation for exchanging bitmapped, monochrome, and full-color images between applications.

tone compression
A reduction in the range of the hues and values in an original.

tone curves
Also known as gamma curves. These are used to smoothly adjust the overall tonal range of an image, or the individual tonal ranges of each color channel.

transparency
A positive photograph on transparent film such as Agfachrome, Kodachrome, or Ektachrome film, usable as copy for color separation and viewed by transmitted light. A positive color image of the original drawing, painting or scene on a colored photographic film is also referred to as a chrome.

transparency scanner
An optical input system for digitizing images from small format positive or negative transparency film.

trapping
A prepress technique which allows for variation in registration during the press run. On the desktop, this is done primarily by allowing an overlap between abutting colors.

TWAIN
An industry standard for software that controls optical input devices such as scanners, film recorders and video capture interface cards. Application programs that support TWAIN allow optical input devices to be controlled from inside the application.

UCR (Undercolor Removal)
A technique for reducing the amount of magenta, yellow and cyan in neutral areas and replacing them with an appropriate amount of black.

USM (Unsharp Masking)
The term comes from a conventional color separation camera technique that uses a unsharp photographic mask to increase contrast between light and dark areas of the reproduction and gives the illusion of sharpness.

white point
A movable reference point that defines the lightest area in an image, causing all other areas to be adjusted accordingly.



There are no terms beginning with 'V', 'X', 'Y' or 'Z' in this glossary.