On-Line Graphics Dictionary
July 6, 2006 12:00 am
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 A Achromatic : Light without color. The quantity of light is the only attribute associated with achromatic light. In physical terms this is the intensity or luminance or in the psychological sense it is the perceived intensity in which case the term brightness is used. Additive Color Model : In an additive color model, colors are defined as a sum of contributions from primary colors. The most commonly used additive color model is the Red-Green-Blue model and is used by computer monitors to produce their display. Additive Primaries : Red, green, and blue (RGB). Lights of these colors, when mixed together in varying intensities, produce any other color in the additive color model. Alpha Channel : The top byte of a 32-bit pixel that is used for data other than color. The channel may hold mask or transparency data. Ambient Light : A global (artificial) illumination level representing infinite diffuse reflections from all surfaces within a scene ensuring that all surfaces are visible (lit) particularly those without direct illumination. Animation : (1) A medium that provides the illusion of a moving scene using a sequence of still images. (2) Techniques used in the production of animated films. In computer graphics this primarily concerns controlling the motion of computer models and the camera. Anti-aliasing : Antialiasing is a method of reducing or preventing aliasing artifacts when rendering by using color information to simulate higher screen resolutions. In one technique, blurred pixels are introduced by filtering the image, or individual elements. The blending of pixel colors on the perimeter of hard-edged shapes, like type, to smooth out undesirable edges (jaggies). Artifacts/Artifact : A classifiable visual error. E.g., a loss of resolution when zooming into an image or incorrect depth sorting due to the painter's algorithm. ASCII : (American Standard Code for Information Interchange) A standard editable format for encoding data. Aspect Ratio : The ratio of the width of an image to its height (x:y). For example, the aspect ratio of an image 640 x 480 pixels is 4:3. Atmospheric Effects : Atmospheric conditions or phenomena that effect the clarity or mood of a scene. Fog and smoke are examples of atmospheric effects. Axis : The Hypothetical linear path. The X, Y, and Z axes (width, height, and depth, respectively) define directions of the 3D universe. The axis along which an object is rotated is the axis of rotation. B Backdrop : A picture that is automatically composited behind a 3D scene. The matte paintings used in traditional movie making are an example of backdrops. Bezier Curve : (1) A spline curve that (in the usual case of a cubic B�zier curve) is represented by four control points defining a cubic polynomial. (2) A curved line segment drawn using the Pen tool that can be reshaped by manipulating its anchor points or direction lines. Binary : In PhotoShop, it is a method for encoding data. Binary encoding is more compact than ASCII encoding. Binary Digit : A binary digit is the smallest unit of information on a computer. Eight bits equal one byte. Bit Depth : The number of bits used to define the shade or color of each pixel in an image. A 1-bit image is black and white. An 8-bit grayscale image provides 256 shades of gray. An 8-bit color image provides 256 colors. A 24-bit image provides over 16 million colors: 8 bits are used for red, 8 are for blue, and 8 for green. Bits per Pixel : The number of bits used to describe the color or intensity of a pixel. For example, using 8 bits for to store a value from the RGB color model would permit 3 bits to be used for both red and green values and 2 bits for the blue value. Blue gets a smaller range because the human eye contains less blue cones and is thus is less sensitive to blue variations. Bitmap : Strictly a one-bit-per-pixel representation for a defined area of a display. In PhotoShop, Bitmap is also a one-channel mode consisting of only black and white pixels. Blur : Reduces areas of high contrast to soften an image. Boolean : An object created by combining two objects using mathematical operators. The two object may be subtracted from each other, merged, or intersected to form the new object. Bounding Box : The smallest regular shaped box that encloses an object, usually rectangular in shape. Brightness : (1)The perceived intensity of a radiating object. (2) The amount of light reflected by a surface. (3) The intensity of a light source. (4) The luminance of a color. Brush : Traditionally in art, a brush is an implement that has hairs or bristles firmly set into a handle and used to paint with. In Photoshop, Painter and other computer graphics applications the brush is a virtual tool replicating the functions of its real world counterpart. Virtual brushes (depending on the program used) can emulate anything from a hard edge pencil, to soft edge airbrush effects, to crayons, oils, watercolour or even impasto style strokes. In most programs you usually have control over the characteristics of the brush stroke and you can also create custom brushes. When using pressure sensitive devices such as a graphics tablet, different characteristics of your brush stroke such as width and opacity can be controlled by factors such as pressure and pen tilt (depending on the device). Bump Mapping : A technique used to increase the realism of a surface by changing how light reflects from that surface. Usually, the surface normal at a given point on a surface is used in the calculation of the brightness of the surface at that point. Part of what gives this techniques its appeal is that the original surface maintains its original (usually smooth) shape, and the bump-mapping distortion is specified by a compact function of shape. This is usually much simpler and more compact than specifying the surface texture by explicitly representing the textured surface. Burn : A PhotoShop tool that is used to darken an area of an image. C CAD : Abbreviation of Computer Aided Design. In the context of graphics, CAD refers to the use of computer based models of objects for visualization or testing as an aid in the design process. Calibration : The process of setting a device to known color conditions. Calibration must be performed externally for devices whose color characteristics change frequently. For example, calibration must be performed on monitors because phosphors lose brightness over time, and on printers because proofers and other digital printing devices can change output when colorant or paper stock is changed. Calibration is not required for most input devices (e.g., scanners and cameras) since these devices are generally self-calibrating. Camera : A virtual viewpoint in world space with position and view direction to provide a view of a scene in the same way as a photographer would position a camera. Canvas : A two-dimensional region of graphics information. The canvas may be displayed on screen or be recorded in off-screen display memory. Canvas Size : The full editable area of an image. Caustics : The concentrated light reflections caused by refraction through a transparent surface. Channel : An image component that contains the pixel information for an individual color. A grayscale image has one color channel, an RGB image has three color channels, and a CMYK image has four color channels. Chroma : (1) A characterization of how much a color differs from both the pure color and the grey of the same intensity. Also called saturation. (2) The color component of a composite video signal. (3) The quality of a color that is the combination of hue and brightness. In the Munsell system of color notation, chroma indicates the purity of a color as measured along an axis; the farther from the axis, the purer the color. Clipboard : An area of memory used to temporarily store selection pixels. The Clipboard is accessed via the Cut, Copy, and Paste commands. Clipping : (1) The selective removal of an object disjoint with the display area or the non-visible parts of an object that does intersect the display area. Parts of an object intersecting the display area may lie outside of the display area or be partially or fully obscured by another intersecting object. (2) Color shift caused by the inability of one color space to reproduce all the colors of another color space. (3) In PhotoShop, the automatic adjustment of colors to bring them into printable gamut. CMYK : (Cyan, Magenta, Yellow, and Black) The four-ink colors used in process printing. Cyan, magenta, and yellow are the three subtractive primaries. CMYK colors are simulated on a computer monitor using additive red, green, and blue light. To color separate an image from PhotoShop, convert it to CMYK Color mode. CODEC : Algorithms used in multimedia. Stands for Compression/Decompression. Color Correction : The adjustment of color in an image to match original artwork or a photograph. Color correction is usually done in CMYK Color mode in preparation for process printing. Color Keying/Chroma Keying : Using the pixel color of one image to designate that pixel data from another image should replace the first pixel's color. The first image might be a binary image, which would select regions of interest from the second image. Another use is in blue-screening, where an actor works against a blue background. In the output image, the blue pixels get replaced by another image. For example, a weather map can be placed behind the weather presenter who is actually standing in front of a blue screen. Color Models : A color model is a method of specifying a color (position) in color space, often using a co-ordinate system. Examples include RGB and the Munsell Color System. Color Separation : The production of a separate printing plate for each ink color that will be used to print an image. Four plates are used in process color separation, one each for Cyan, Magenta, Yellow, and Black. An addition plate is used for each spot color. Color Space : A mathematical space defining a range and encoding of colors. E.g. see RGB, LUV, HSV, HSL, YIQ, YUV and XYZ. Color Table : The color palette of up to 256 colors of an image in Indexed Color mode. Composite Printer : The printer used to make a composite color image of a file. This printer can be used for proofing or for final output. Compositing : The process of combining multiple images into a single image. Usually this is performed in films to make a computer graphics generated character appear on a previously filmed background. The term is also used in traditional photographic manipulation to refer to the process by which cel animation is recorded onto film under a rostrum camera. In film the 'mechanical' process is usually called matte photography (see color keying), and the process, when used in film sequences is ambiguously called traveling matte. Compression : The process by which some of an image's data is either stored in patterns or eliminated in order to reduce the images file size. Continuous-Tone Image : An image, such as a photograph, in which there are gradual transitions between shades or colors. Contract Proof : The proof (e.g., Dupont WaterProof or Imation MatchPrint) of a color printing job that is the basis of a contract between a printer and a client. The appearance of the contract proof should represent the appearance of final printed piece. Contrast : The range of colors in an image. Increasing the contrast of a color palette makes different colors easier to distinguish, while reducing the contrast makes them appear washed out. Crop : A tool used to trim away part of an image. Crop Marks : Short, fine lines that are placed around the edges of a page to designate where the paper is to be trimmed at a print shop. D Data Rate : Transfer speed of a specific device. DCS 2.0 : (Desktop Color Separation) A file format for saving a CMYK image for color separation, with the option for saving spot color channels and alpha channels, and an optional low resolution file for previewing and laser printing. Depth of Field : The distance between the closest and farthest objects in focus within a scene as viewed by a lens at a particular focus. Diffuse : Light that is reflected from an object's surface, regardless of the angle from witch its viewed. Dissolve : An animation effect that is a transition between two sequences involving a fade from one directly to the other. Dither : The mixing of adjacent pixels to simulate additional colors when available colors are limited, such as on an 8-bit monitor or an 8-bit palette. Dithering : One of many processes for reducing the total number of colors present in an image while retaining visual fidelity. Dithering can be done by interleaving pixels of selected colors to locally approximate the desired color. Dithering can be applied to either a color or a grayscale color space and may be necessary due to a limited number of colors available on the display device. Dodge : To bleach (lighten) an area of an image. Dot Gain : Measured by the increase in size of a midtone dot, the spreading of dots during platemaking or on a printing press as wet ink is pushed into the paper and possibly absorbed by it, which causes colors or shades to look darker. DPI : (Dots per inch) A unit that is used to measure the resolution of a printer or image setter. Dpi is sometimes used to describe the input resolution of a scanner, but "ppi" is the more accurate term. Duotone : A grayscale image that is printed using two plates to enhance its tonal depth. DXF : A standard 3D file format that was originally developed by Autodesk to exchange CAD data between various software applications. This format only offers support for basic geometric information. Dye Sublimation : A continuous-tone printing process in which a solid printing medium is converted into a gas before it hits paper. E EPS : Encapsulated PostScript, the file format based on Adobe PostScript. Primarily used to define vector graphics (i.e., geometrical shapes), it can also be used to contain and provide instructions for rendering image (i.e., pixel-based) data. In the case of PhotoShop, an optional PICT or TIFF image for screen display is included too. EPS is a commonly used format for moving files from one application to another and also for color separation. F Feather : Fades an area over a specified number of pixels. Fill/Flood Fill : These are techniques for coloring areas bounded by line edges. The algorithms that fill interior-defined regions (the largest connected region of pixels whose values are the same as a given starting pixel) are called flood fill algorithms. Filter : 1) An optical device that selectively attenuates the intensity of light passing through it according to the light's properties. Common filters attenuate light according to either wavelength or polarization state. 2) An algorithm that selectively modifies the intensity or color of image data according to the image's properties. 3) An element (software or hardware) which takes in a stream of data and produces a stream of results, on average one output for each input. Foreground Color : The color that is applied when a painting tool is used, type is created, or the stroke command is applied. Four-color Process : The printing process that reproduces colors by combining, cyan (C), magenta (M), yellow (Y), and black (K) inks. This process is alternately called four-color printing, CMYK printing, or process printing. FPS : Frames Per Second. The rate at which animations are displayed. Frame : A still two-dimensional image. Often a frame is a raster image as used in the frame buffer of a graphics display system. In computer animation frames per second is a measurement of the number of still frames displayed in one second to give the impression of a moving image. Frame Rate : The frame rate of a video source is determined by the speed at which it completes the rendering of a new image. This is limited by both the speed at which image data can be created and the rate at which video images can be presented on a display. For example the NTSC system redraws at 30Hz, PAL is 25Hz and computer displays are now usually 72-75Hz. Frame Size : A term used to refer to the dimensions of the array of pixels forming a frame of an animation, or alternatively the memory requirement and hence indirectly the resolution and dimensions. G Gamma : The values produced by a monitor from black to white are nonlinear. If you graph the values, they form a curve, not a straight line. Gamma defines the slope of that curve at halfway between black and white. Gamma adjustment compensates for the nonlinear tonal reproduction of output devices such as monitor tubes. Gamut : The total range of colors produced by a device. A color is said to be "out of gamut" when its position in one device's color space cannot be directly translated into another device's color space. GIF : Graphic Interchange Format. This file format is commonly used on the internet. Gradient Fill : In PhotoShop, a graduated blend between the Foreground and Background colors that is produced using the Gradient tool. Grayscale : A color space where colors are represented by their luminance values only, i.e. saturation and hue are zero. An image that contains black, white, and up to 256 shades of gray, but no color In PhotoShop, Grayscale is a one-channel image mode. H Halftone Screen : A pattern of tiny dots that is used for printing an image to simulate continuous tones. Hard Proof : The printed proof of a document created to preview how colors will look when reproduced on a specific output device, usually a commercial printing press. A hard proof may be produced using a laminate contract proofing system (e.g., Imation MatchPrint) or a tightly calibrated digital printer designed for proof creation. Highlight : The area of a glossy object over which specular reflection can be viewed. It is normally the color of the light source, not of the object. Histogram : A graph showing the number of pixels at each level of brightness in an image. HSB : A three-coordinate, device-independent color model. The HSB coordinates define colors in terms of Hue, Saturation, and Brightness. HSL/Hue-Saturation-Lightness : HSL, also known as HSI (Hue-Saturation-Intensity) is a color space used to represent images. HSL is based on polar coordinates, while the RGB color space is based on a three-dimensional Cartesian coordinate system. Intensity is the vertical axis of the polar system, hue is the relative angle and saturation is the planar distance from the axis. HSL is thought to be more intuitive to manipulate than RGB space. For example, in the HSI space, to change red to pink requires only changing the saturation parameter. < HSV/Hue-Saturation-Value : A color space that describes color using three basis components: hue, saturation and brightness. Hue : The wavelength of light of a pure color that gives a color its name--such as red or blue--independent of its saturation or brightness. I Illuminance : The amount of light falling into a patch of unit surface area. It is measured in lux. Imagesetter : A high-resolution printer (usually between 1,270 and 4,000 dpi) that generates paper or film output from a computer file. Image File Format : A representation (usually binary) used by a computer system as an agreed format to store an image. Examples of image file formats include the Graphics Interchange Format (GIF) and Tagged Image File Format (TIFF). Inbetweening : Inbetweening is the generation of intermediate transition positions from a given start and end point or keyframes. This technique is often used in animation, where a lead artist generates the beginning and end keyframes of a sequence (typically 1 second apart), a breakdown artist does the breakdowns (typically 4 frames apart), and an �inbetweener� completes the rest. Indexed Color : In PhotoShop, an image mode in which there is only one channel and a color table that can contain up to 256 colors. All the colors in an Indexed Color image are displayed on its table. Indexed 16 and 256 Color Images : An indexed color image consists of a set of references to values stored in a color table or palette. The palette, which is often contiguous in an image file, lists all the colors as sets of coordinates in color space. An indexed 16-color image contains a palette with 16 color entries (4 bits), whereas in an indexed 256 color image 256 colors are listed (8 bits). Interpolation : A process that occurs automatically when an image's dimensions or resolution are changed which results in re-coloring the pixels. Interpolation may cause an image to look blurry when it's printed. You can choose an interpolation method in PhotoShop from slower, but better, to faster but lower quality. Interlaced Display : A technique for displaying images at a higher resolution than the monitor. Two images consisting of every second row of pixels are alternately displayed during every screen refresh (e.g. every fiftieth of a second). There is hence a flickering artifact. International Color Consortium (ICC) : The group established by eight industry vendors (including Adobe Systems) for the purpose of creating, promoting, and encouraging the standardization and evolution of an open, vendor-neutral, cross-platform color management system architecture. Inverse Kinematics (IK) : The study of how movement of a body part affects other attached body parts. Invert : To reverse an image's light and dark values and/or colors. J JPEG : Acronym for Joint Photographic Experts Group. Commonly used to indicate a pixel-based graphic file format, JPEG is actually a compression method used mostly for continuous tone images. JPG : An image format commonly used on the internet. It does not support layers, transparency or alpha channel data. K Kern : To adjust the horizontal spacing between a pair of characters. Keyframe : An image that is stored in some way to be used as a reference point. Key frames are often used in animation. L LAB Model : The color model is based on the model proposed by the Commission Internationale d'Eclairage (CIE). LAB color is designed to be device-independent and perceptually uniform. LAB color consists of a luminance or lightness component (L*) and two chromatic components: the A* component (from green to red) and the B* component (from blue to yellow). Layer : A level of an image that can be edited independently from the rest of the image. Leading : The spacing between lines of type, measured from baseline to baseline. Lightness : The lightness (or brightness) of a color, independent of its hue and saturation. Luminosity : The distribution of an image's light and dark values. Line Drawing : An image created only from points connected by lines. It can be described using a series of end-point coordinate information. This can be combined with a weight which denotes the thickness of the connecting line. Local Light Source : Light source that directly (i.e., not by reflection or transmission) illuminates a point on a surface. LPI : (Lines per inch/halftone frequency/screen frequency) The unit that is used to measure the frequency of rows of dots on a halftone screen. Luminance : The absolute quantity of radiation emitted from a given light source or the brightness of a surface determined by the amount of light it emits or reflects. Luminosity : The relative quantity of radiation emitted by a light source. LUV Space : A color space similar to the XYZ model, except that the components are scaled to be perceptually linear. The human eye perceives brightness on a logarithmic scale, and hence LUV components are logs of the corresponding XYZ values. M Mask : An area that can be protexted and isolated from changes applied to the rest of the image. N Noise : Random recoloring of pixels to create a grainy pattern. NURBS : Non-Uniform Rational B-Splines, are mathematical representations of 3-D geometry that can accurately describe any shape from a simple 2-D line, circle, arc, or curve to the most complex 3-D organic free-form surface or solid. Because of their flexibility and accuracy, NURBS models can be used in any process from illustration and animation to manufacturing. O Opacity : The density of a layer or color. P Parallel Light : A light that casts rays that are perfectly parallel to one another. Pitch : The rotation of an object. Usually forward and back. Pixels : (Basic image elements) The individual dots that are used to display an image on a computer monitor. Image size and resolution are defined in terms of number of pixels. Pixel Depth : The number of bits used to generate a color at each pixel. For instance a pixel depth equal to one means that only black and white colors could be displayed; with a pixel depth equal to four, sixteen different colors could be displayed. Plug-in Module : Third-party software that is loaded into the PhotoShop Plug-ins folder which enables it to be accessed from a PhotoShop menu. Or, a plug-in module that comes with PhotoShop that is used to facilitate Import, Export, file format conversion, or other operations. PNG : Portable Network Graphics. A web based format that supports one alpha channel and transparency. Point : A unit of measure that is used to describe type size (measured from ascender to descender), leading (measured from baseline, to baseline) and line width. Posterize : Produces a special effect in an image by reducing the number of shades of gray or colors to a specified (usually low) number. PostScript : The page description language created and licensed by Adobe Systems Inc. that is used to display and print fonts and images. POV : (Point of View) The position and angle used when viewing a scene. PPI : (Pixels per inch) The unit that is used to measure the resolution of a bitmapped image. Primary Colors : Colors, usually three, which are combined to produce the full range of other colors within a color model. All non-primary colors are mixtures of two or more primary colors. Red, green, and blue are the primary colors of the additive color model. Cyan, magenta, and yellow are the primary colors of the subtractive color model. Process Color : Inks that are used to print an image from four separate plates, one each for Cyan (C), Magenta (M), Yellow (Y), and Black (K). In combination, they produce an illusion of an even wider range of colors. Process Colors : The subtractive primary colors, cyan, magenta, and yellow (CMY), used in process printing. Purity : The degree to which a color is saturated. Q QuickTime : Developed by Apple Computer. A type of video file format. R Radiosity : The level of light reflected off of or scattered by light falling across surfaces. It is a natural occurence that object's surfaces do not absorb all light rays and so reflect some back into the surrounding area. Render : The process of building a 2D image from the data contained in a 3D scene. Resolution : This indicates the number of pixels per image. It is often represented in this format: where N and M are the number of pixels per column and row respectively. RGB Color Model : The RGB (red, green, blue) color model describes a color as a positive combination of three appropriately defined red, green and blue primaries. They represents the additive color model, where 0% of each component yields black and 100% of each component yields white. Red, green and blue are the additive complements of cyan, magenta, and yellow respectively. RGB True Color : An RGB color system with 24 bits per pixel color resolution. This gives a choice of over 16 million colors per pixel. Such a system is generally known as a true color or full color system. Roll : The rotation of an object. Usually Left to right (tilting). Gives the illusion that your horizon is tilted. S Saturation : A perceptual term referring to the colorimetry quantity 'excitation purity' of a color. Hue can be used together with saturation and luminance to define a HSL color space. Scaling : The process in which the size of an image or geometric representation is modified by multiplying each component of the representation's coordinates by constant factors. Scaling and many other simple transformations can be done simultaneously if positions and directions are represented in homogeneous coordinates. Screen Capture : The process of capturing what is currently displayed on your monitor. Separations Color : Any color in a document that needs to print as a separate plate on a printing press. Shading : Coloring a surface according to its incident light. The color depends on the position, orientation and attributes of both the surface and the sources of the illumination. Snap To : The process of moving a point to a specific grid location. Specular : The highlight of an object that has a shiny surface. Soft Proof : In a color-managed workflow, the use of ICC device profiles to preview document colors directly on your monitor as they will be reproduced by a specific device. Spot Color : Also called pre-mixed inks, the inks used for printing a specific color. Spot color inks are cost-effective for two- or three-color printing and may also be used for colors that process printing cannot adequately produce. Use spot color inks when: you need three or fewer colors and you will not be reproducing process-color photographs; or you want to print logos or other graphic elements that require precise color matching. Spotlight : A light that casts its rays in a cone shaped pattern. Subtractive Color Model : The color model in which colors are produced by combining various percentages of the subtractive primaries, cyan, magenta, and yellow. Four color printing uses cyan, yellow, and magenta (CMY) inks. In theory, combining 100% of each cyan, magenta, and yellow should produce a pure black. In practice, however, the combining of cyan, magenta, and yellow inks does not produce a pure black due to impurities in inks. For this reason, black ink (K) is used in addition to the cyan, magenta, and yellow inks in four-color printing. T Tesselation : A technique to construct a surface by a small set of figures which fit together. They are drawn repeatedly over the entire plane leaving no gaps. Texture Map : A bitmap used to texture a 3D polygon model, including adjustments for perspective correction, where vertices of the object model are mapped onto the 2D texture bitmap. In addition to color and brightness, textures may also be encoded with the properties of transparency and specular reflectivity. This kind of texture may also be procedural in nature. A possible side-effect of texture mapping occurs unless the renderer can apply texture maps with correct perspective. Perspective-corrected texture mapping involves an algorithm that translates texels, or pixels from the bitmap texture image, into display pixels in accordance with the spatial orientation of the surface. TGA : (Targa) A photorealistic graphics file format originally designed for systems with a Truevision display adapter. It supports 1 to 32 bit images, and professional features like an alpha (mask) channel, gamma settings and a built-in thumbnail image. Thumbnail : A smaller representation of a larger image. TIFF : Acronym for Tag Image File Format; the graphics file format first released by Aldus Corporation in 1986. TIFF is the standard file format used for most digital imaging programs. TIFF is a highly extensible format that allows image data to be tagged with additional information through an image file directory (IFD) which contains header-type information without actually being a part of the file's header. TIFF can be used for black-and-white, grayscale, RGB, and CMYK images. TIFF can be uncompressed or may use any of a variety of compression methods, though TIFF most commonly uses LZW compression. Torus : A primitive that looks like a donut. Transparency : The ratio of the amount of light passing through a material to the amount of light incident on the material. True Color : The common name for 24-bit color. TWAIN : An industry wide standard for devices such as scanner and digital cameras to interface with software programs. U V Value : The relative lightness or darkness of a color. Vanishing Point : A point in a perspective projection where parallel lines not parallel to the projection plane converge. A finite 2D projection of a point at infinity in 3D. Vector : A list of numbers, typically Cartesian coordinates or a direction in 2D or 3D. Vector Graphic : The earliest computer graphics displays were drawn on so-called vector displays, because the electron beam which produced the image was under software control. The beam followed a chain of vectors (i.e. a polyline) from one point to another. Vector graphics is sometimes referred to as line-drawing graphics. VRML : Virtual Reality Modeling Language. A 3D model description format suited to transfer on the WWW. W Watermark : Information embedded in an image that is invisible to the human eye. Can be used for copyrighting images. Wireframe : A wire mesh representation of a 3D object. X XYZ Color Space : A color model in which X specifies the red component and Y the green component. The blue component is 1-X-Y (the color components are scaled so that R+G+B=1). Z specifies the brightness. Y Yaw : The rotation of an object. Usually turning left to right. YIQ Color Space : A chrominance/luminance color space model used in the American NTSC television standard, Y specifies luminance, I and Q specify chrominance. I specifies the red-orange/cyan (or blue-green) component, and Q specifies the green/magenta (or purple) component. YUV Color Palette : A chrominance/luminance color space model used in the British PAL television standard, Y specifies luminance, U and V specify chrominance. U specifies the blue/yellow component, and U specifies the red/cyan (or blue-green) component. Z Zooming : Viewing an image at different sizes. Zooming in creates an enlarged view of a portion of the scene in the image frame. Zooming out does the reverse.