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:
- Run Length Encoding (RLE) is a lossless compression technique
supported by the Photoshop and TIFF file formats and some common Windows
file formats.
- Lemple-Zif-Welch (LZW) is a lossless compression technique
supported by TIFF, PDF, GIF, and Post Script language file formats.
This technique is most useful in compressing images that contain large
area of single color, such as screenshots or simple paint images.
- Joint Photographic Experts Group (JPEG) is a lossy compression
technique supported by JPEG, PDF, and PostScript language file formats,
JPEG compression provides the best results with continuous-tone images,
such as photographs.
- CCITT encoding is a family of lossless compression techniques
for black and white images that is supported by the PDF and PostScript
language file formats. (CCITT is an abbreviation for the French spelling
of International Telegraph and Telekeyed Consultive Committee.)
- ZIP encoding is a lossless compression technique supported
by the PDF file format. Like LZW, ZIP compression is most effective
for images that contain large areas of single color.
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-
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