     |
|
Terms |
  |
|
Graphics Terminology aliasing- the process by which smooth curves and other lines become jagged because the resolution of the graphics device or file is not high enough to represent a smooth curve. Smoothing and anti-aliasing techniques can reduce the effect of aliasing. alpha channels- a portion of each pixelÕs data that is reserved for transparency information. A 32-bit graphics system contains four channels0three 8-bit channels for red, green, and blue (RGB) and one 8-bit alpha channel anchor- in desktop publishing, to fix a graphical object so that its position relative to some other object remains the same during repagination. Frequently, for example, you may want to anchor a picture next to a piece of text so that they always appear together. antialiasing-a software technique for diminishing jaggies- stairsteplike lines that should be smooth. Jaggies occur because the output device-the monitor or printer-doesnÕt have a high enough resolution to represent a smooth line. Antialiasing reduces the prominence of jaggies by surrounding the stairsteps with intermediate shades of gray ( for gray-scaling devices) or color (for color devices). Although this reduces the jagged appearance of the lines, it also makes them fuzzier. Another method for reducing jaggies is called smoothing, in which the printer changes the size and horizontal alignment of dots to make curves smoother. Antialiasing is sometimes called oversampling. autotracing-the process of converting a bit-mapped image (or raster image) into a vector image. In a bit-mapped image, each object is represented by a pattern of dots, while in a vector image every object is defined geometrically. Most autotracing packages read files in a variety of bit-mapped formats (PCX and TIFF are the most common) and produce a file in a vector format such as EPS. The conversion techniques used, and the accuracy of the conversion process, differ from one package to another. Auto tracing is particularly useful for manipulating image produced by and optical scanner. Scanners produce bit-mapped image that cannot be manipulated by sophisticated tools until they have been converted into a vector format through autotracing. Bézier curve-bez-ee-ay, curved lines defined by mathematical formulas. Nearly all draw programs support Bˇzier curves. Bˇzier curves employ at least three points to define a curve. The two endpoints to the curve are called anchor points. The other points, which define the shape of the curve, are called handles, tangent points, or nodes. Attached to each handle are two control points. Attached to each handle are two control points. By moving the handles themselves, or the control points, you can modify the shape of the curve. bit map-a representation, consisting of rows and columns of dots, of a graphics image in computer memory. The density of the dots, known as the resolution, determines how sharply the image is represented. This is often expressed in dots per inch (dpi) or simply by the number of rows and columns, such as 640 by 480. Bit-mapped graphics are often referred to as raster graphics. The other method for representing images is known as vector graphics or object Šoriented graphics. With vector graphics, images are represented as mathematical formulas that define all the shapes in the image. Vector graphics are more flexible than bit-mapped graphics because they look the same even when you scale them to different sizes. In contrast, bit-mapped graphics become ragged when you shrink or enlarge them. Fonts represented with vector are called scalable fonts, outline fonts, or vector fonts. The best-known example of a vector font system is PostScript. Bit-mapped fonts, also called raster fonts, must be designed for a specific device and a specific size and resolution. bit-mapped graphics-refers to hardware and software that represent graphics images as bit maps. The other method of representing images is known as vector graphics. bit- 1-bit, 8-bit, 16-bit, 24-bit, and 32 bit- graphics are often described by the number of bits used to represent each dot. A 1-bit image is monochromatic, an 8-bit image supports 256 colors or grayscale, and a 24-bit or 32-bit graphic supports true color. bleed- text or graphics that extend all the way to the edge of the paper. Most printers cannot print all the way to the edge of the paper, so the only way to produce a bleed is to print on paper larger than the final page size and then trim the paper. capture-to save a particular state of a program. The term capture often refers to saving the information currently visible on a display screen. You can capture the screen to a printer or to a file. The act of saving a display is called a screen capture. Video capture refers to storing video images in a computer. See screen capture. clip-in computer graphics, to cut off a portion of a graphic at a defined boundary. Most bit-mapped graphics utilities provide a clip feature that enables you to draw a window around an object and clip everything outside of the window. clip art-electronic illustration that can be inserted into a document. Many clip-art packages are available, some general and others specialized for a particular field. Most clip-art packages provide the illustration in several file formats so that you can insert them into various word processing systems. CMYK-short for C(yan)-M(agenta)-Y(ellow)-(Blac)K, and pronounced as separate letters. CMYK is a color model in which all colors are described as a mixture of these four process colors. CMYK is the standard color model used in offset printing for full-color documents. Because such printing uses inks of these four basic colors, it is often called four-color printing. In contrast, display devices generally use a different color model called RGB, which stands for R(ed)- G(reen)-B(lue). One of the most difficult aspects of desktop publishing in color is color matching-properly converting the RGB colors into CMYK colors so that what gets printed looks the same as what appears on the monitor. The most recent Windows and Macintosh operating systems include a color management system (CMS) to assist in color matching. color depth-the number of distinct colors that can be represented by a piece of hardware or software. Color depth is sometimes referred to as bit depth because it is directly related to the number of bits used for each pixel. A 24-bit video adapter, for example, has a color depth of 224 (about 16.7 million) colors. One would say that its color depth is 24 bits. color separation-the act of decomposing a color graphic or photo into single-color layers. For example, to print full-color phots with an offset printing press, one must first separate the photo into the four basic ink colors: cyan, magenta, yellow and black (CMYK). Each single color layer is then printed separately, one on top of the other, to give theimpression of infinite color. This type of color separation, mixing three or four colors to produce an infinite variety of colors, is called process color separation. Another type of color separation, called spot color separation, is used to separate colors that are not being mixed. In this case, each spot color is represented by its own ink, which is specially mixed. Spot colors are effective for high lighting text, but they cannot be used to reproduce full-color images. Many modern desktop publishing systems are now capable of producing color separations for graphics stored electronically. This capability is essential if you want to create full-color documents on your computer and then print them using an offset printer. You donÕt need to perform color separation if you are printing directly to a color printer because in this case the printer itself performs the color separation internally. compression-storing data in a format that requires less space than usual. Compression data is the same as packing data. Data compression is particularly useful in communications because it enables devices to transmit the same amount of data in fewer bits. There are a variety of data compression techniques, but only a few have been standardized. The CCITT has defined a standard data compression technique for transmitting faxes (Group 3 standard) and a compression standard for data communication through modems (CCITT V.42 bis). In addition, there are file compression formats, such as ARC and ZIP. Certain types of data, such as bit-mapped graphics, can be compressed to a small fraction of their normal size. computer imaging-a field of computer science covering digital images-images that can be stored on a computer, particularly bit-mapped images. Computer images are a wide field that includes digital photography, scanning, and composition and manipulation of a bit-mapped graphics. Computer images are often called digital imaging. continuous tone-refers to images that have a virtually unlimited range of color or shades of grays. Photographs and television images, for example, are continuous-tone images. In contrast, computer hardware and software are digital, which means that they can represent only a limited number of colors and gray levels. Converting a black and white continuous-tone image into a computer image is known as gray scaling. Continuous-tone printers can print each dot in many different shades of lightness and darkness. Though this isnÕt true continuous-tone because the level of shades is limited, there are enough shades (256 or more) so that the difference between one shade and the next is imperceptible to the human eye. crop-in computer graphics, to cut off the edges of an image to make it the proper size or to remove unwanted parts. Most graphics applications allow you to crop images with a clip feature. digitizing tablet, graphics tablet, electronic tablet-an input device that enable you to enter drawings and sketches into a computer. A digitizing tablet consists of an electronic tablet and a cursor or pen. A cursor (also called a puck) is similar to a mouse, except that it has a window with cross hairs for pinpoint placement, and it can have as many as 16 buttons. A pen (also called a stylus) looks like a simple ballpoint pen but uses and electronic head instead of ink. The tablet contains electronics that enable it to detect movement of the cursor or pen and translate the movements into digital signals that it sends to the computer. dithering-creating the illusion of new colors and shades by varying the pattern of dots. Newspaper photographs, for example, are dithered. If you look closely, you can see that different shades of gray are produced by varying the patterns of black and white dots. There are no gray dots at all. The more dither patterns that a device or program supports, the more shades of gray it can represent. In printing, dithering is usually called halftoning, and shades of gray are called halftones. Note that dithering differs from gray scaling. In gray scaling, each individual dot can have a different shade of gray. DPI-dots per inch (print) indicates the resolution of images. The more dots per inch, the higher the resolution. A common resolution for laser printers is 600 dots per inch. This means 600 dots across and 600 dots down, so there are 360,000 dots per square inch. file size- high quality (resolution, color, etc.) equals a larger file and thus more storage and manipulation problems file compression- (storing a file so that it takes up less room on a disk) Many image file formats use compression techniques to reduce the storage space required by bitmap image data. Compression techniques are distinguished by whether they remove detail and color from the image. Lossless techniques compress image data without removing detail; lossy techniques compress images by removing detail. The following are commonly used compression techniques:
fill-in graphics applications, to paint the inside of an enclosed object filter-in paint programs and image editors, a filter is an effect that can be applied to a bit map. graphics-pertains to any computer device or program that makes a computer capable of displaying and manipulating pictures. This includes paint programs, illustration/design programs, presentation graphics software, animation software, CAD software, and desktop publishing. gray scaling, (gray scale-a range of gray between total white and total black)-the use of many shades of gray to represent an image. Continuous Štone images such as black-and-white photographs, use as almost unlimited number of shades of gray. Conventional computer hardware and software, however, can represent only a limited number of shades of gray (typically 16 or 256). Gray scaling is the process of converting a continuous-tone image to an image that a computer can manipulate. Note that gray scaling is different from dithering. Dithering simulates shades of gray by altering the density and pattern of black and white dots. In gray scaling, each individual dot can have a different shade of gray halftone-in printing, a continuous-tone image, such as a photograph, that has been converted into a black-and-white image. Halftones are created through a process called dithering, in which the density and pattern of black-and-white dots are varied to simulate different shades of gray. In conventional printing, halftones are created by photographing an image through the screen. The screen frequency, measured in lines per inch, determines how many dots are used to make each spot of gray. In theory, the higher the screen frequency (the more lines per inch), the more accurate the halftone will be. However, actual screen frequencies are limited by the technology because higher screen frequencies create smaller, more tightly packed dots. If you are printing on a low-resolution device, therefore, you may get better results with a lower screen frequency. Modern desktop publishing systems can create halftones by simulating the conventional photographic process. This is why some programs allow you to specify a screen frequency even when no actual screen is used. handle-in many applications, when you select a graphical object, an outline of the object appears with small boxes. Each box is a handle. By dragging the handles, you can change the shape and size of the object. image map-a single graphic image containing more than one hot spot. For example, imagine a graphic of a bowl of fruit. When you click on a banana, the system displays the number of calories in a banana and when you click on an apple, it displays the number of calories in an apple. Image maps are used extensively on the World Wide Web. Each hot spot in a Web image map takes you to a different Web page or to another area of the same Web page. image processing-analyzing and manipulating images with a computer. Image processing generally involves three steps: 1. Import an image with an optical scanner or directly through digital photography. 2. Manipulate or analyze the image in some way. This stage can include image enhancement and data compression. 3. Output the result. jaggies-stairstep lines that appear where there should be smooth curves or smooth, straight diagonal lines. Jaggies can occur for a variety of reasons, the most common being the output device (display monitor or printer) does not have enough resolution to portray a smooth line. In addition, jaggies often occur when a bit-mapped image is converted to a different resolution. This is one of the advantages that vector graphics has over bit-mapped graphics-the output looks the same regardless of the resolution of the output device. The effect of jaggies can be reduced somewhat by a graphics technique known as antialiasing. Antialiasing smoothes out jagged lines by surrounding the jaggies with shaded pixels. In addition, some printer can reduce jaggies with a technique known as smoothing. line art-a type of graphic consisting entirely of lines, without any shading. Most art produced on computers is NOT line art because the computer makes it so easy to add subtle shadings. links-to paste a copy of an object into a document in such a way that it retains its connection with the original object. Updates to the original object can be reflected in the duplicate by updating the link. lossless compression-refers to data compression techniques in which no data is lost. They group information so that file is stored in compact form, up to about 50% of the original. Used when compressing data and programs. lossy compression(JPEG)- refers to data compression techniques in which some amount of data is lost. Lossy compression technologies attempt to eliminate redundant or unnecessary information. Used for images 24 bits or higher. Graphics, audio, and video can tolerate lossy compression. marquee-in graphics software, a sizable and movable frame that identifies a selected portion of a bit-mapped image. The marquee frame can be rectangular in shape or, in some cases, irregular. A lasso tool, for example, enables you to select all contiguous portions of an image that share the same color. mask-a filter that selectively includes or excludes certain values. moiré-an undesirable pattern that appears when a graphic image is displayed or printed with an inappropriate resolution. Moirˇ patterns are difficult to predict because they result from a complex combination of parameters: the size of the image, resolution of the image, resolution of the output device, halftone screen angle, and so on. If youÕre planning to print a graphic image (particularly a bit-mapped image) on a high-resolution printer, itÕs a good idea to print a test page first to see if there are any moirˇ patterns. If there are, you can sometimes eliminate them by changing the resolution of the printout, resizing the image, or changing the angle of the halftone screen. monochrome-one color. Actually, with monochrome monitors there are two colors: one for the foreground and one for the background. Graphic images can be monochrome, grayscale, or color. morphing-short for metamorphosing, morphing refers to an animation technique in which one image is gradually turned into another. Many advanced animation programs support some type of morphing feature. object-oriented graphics-the representation of graphical objects, such as lines, arcs, circles, and rectangles, with mathematical formulas. This method of describing objects enables the system to manipulate the objects more freely. In an object-oriented system, for example, you can overlap objects but still access them individually, which is difficult in a bit-mapped system. Also, object-oriented images profit from high-quality output devices. The higher the resolution of a monitor or printer, the sharper an object-oriented image will look. In contrast, bit-mapped images always appear the same regardless of a deviceÕs resolution. One of the most widely used formats for object-oriented graphics is Post Script. PostScript is a page description language (PDL) that makes it possible to describe objects and manipulate them in various ways. For example, you can make objects smaller of larger, turn them at various angles, and change their shading and color. A font described in Post Script, therefore, can easily be transformed into another font by changing its size or weight. Object-oriented fonts are called outline fonts, scalable fonts, or vector fonts. Object-oriented graphics is also called vector graphics, whereas bit-mapped graphics is sometimes called raster graphics. palette- pixel- pixel depth- plot- polyline- PPI- resolution- RGB-One of the most difficult aspects of desktop publishing in color is color matching-properly converting the RGB colors into CMYK colors so that what gets printed looks the same as what appears on the monitor. The most recent Windows and Macintosh operating systems include a color management system (CMS) to assist in color matching. scale- scanner, flatbed scanner- screen capture- spline- sprite- tags- text mode- vector graphics- video mode-
Typography Terminology ascender- baseline- boldface- bullet- caps- Courier font- CPI- descender- dingbat- drop cap- fixed pitch- font- font family- hyphenation- inellifont- italic- kerning- leading- lowercase- micro-justification- microspacing- monospacing- outline font- pica- pitch- proportional font- proportional spacing- romans- sans serif- scalable font- serif- superscript- TrueType- TWIP- typeface- uppercase- x-height- |
