Glossary
Select the first letter of the word from the list above to jump to appropriate section
of the glossary. If the term you are looking for starts with a digit or symbol, choose the
'#' link.
- A -
Additive Primary Colors
Red, Green, Blue; the 3 colors used to create all other colors when
direct, or transmitted, light is used (as in a video monitor). They are called additive
primaries, because when these three colors are superimposed they produce white.
Anti-Aliasing
A method of filling in data which has been missed due to under-sampling. In
imaging this usually takes on the process of removing jagged edges by interpolating values
in-between pixels of contrast. These methods are most often used to remove or reduce the
stair-stepping artifact found in digital high contrast images.
Archival Refers to length of time a medium will remain
100% true without loss.
Area of Interest (AOI)
A rectangle within an image defined as two points within the image. Thus,
an AOI can be written as (x1,y1)-(x2,y2). Because of its definition all AOI are parallel
with the image's axes. See also ROI.
Aspect Ratio
The proportion of an image's size given in terms of the horizontal length
verses the vertical height. An aspect ratio of 4:3 indicates that the image is 4/3 times
as wide as it is high.
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- B -
Bezier Curve
A curve created from endpoints and two or more control points that serve as
positions for the shape of the curve. Originated by P. Bezier (~1962) for the use in car
body descriptions.
Bit Block Transfer
A raster operation that moves a block of bits representing some portion of
an image or scene from one location in the frame buffer to another. Usually written as
"bit blt"
Bit Blit
See Bit Block Transfer
Bitmap
An image is called a bit map if it contains a value for each of its pixels.
This is the opposite of vector images where a small set of values can generate an object.
Bit Plane
A hypothetical 2-D plane containing a single bit of memory for each pixel in a image. If
each 8-bit pixel is thought of as a stack of 8 coins, and an image as many rows and
columns of these stacked coins then the 3rd bit plane would be the plane consistingof the
3rd coin from each stack.
Blip: A mark put on a microfilm frame for
counting or timing purposes.
BMP
file format extension for bitmap images. Format originator:
Microsoft Corporation 16011 NE 36th Way, Box 97917/Redmond, WA 98073
Bounding Rectangle
The smallest rectangle that fits around a given object. In imaging the rectangle is
usually rotationally restricted to be parallel to both image axes.
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- C -
Camera, Planetary: A microform camera
that takes pictures of documents and generates microfilm images. The document is held
still on a copyboard while film is being exposed. Once the document is recorded, it is
replaced with the next document to be filmed and the film in the camera is advanced.
Camera, Rotary or Flow: Another camera that takes pictures of documents and
generates microfilm. This one is more like a paper scanner. Instead of an overhead camera
taking pictures, it has a CCD-array-like slit. The paper and film move past the slit
simultaneously. "Since you have two moving elements, your image quality suffers a
bit," says Wayne Sandberg, president of Amitech. "Also it captures the front and
back on the same width of film, so it has to be reduced about 40 times; therefore, the
resolution is not as high as [film shot with a planetary camera]. [It's] not as good for
fine print. The benefit is that the paper is filmed and scanned in one pass and is
available in real time."
Cartesian Coordinates
The usually 2 dimensional equally spaced grid iron that uniquely
assigns every point in the plane, (one and only one), coordinate pair; (x,y). In imaging
each point is usually referred to as a pixel and the x and y values take on integer
values. Most images use the top-left as the (0,0), or origin. See also Coordinates.
Chroma-key
An image blending function which
replaces pixels of a specified hue range with pixels from a second image. This is often
referred to the weatherman effect because most weather forecasters use a solid blue or
green background to make it look as if they are standing in front of a huge weather map.
It is important to remember that it is the hue that is used in the blending function and
not the intensity or saturation.
C.I.E.
See Commission Internationale de
l'Eclairage.
Commission Internationale de l'Eclairage
In English: International
Commission of Illumination. A standards organization which provides specifications for the
description of device independent color.
Closing
See Morphology
CMY & CMYK
Cyan, Magenta, Yellow, (K)black.
Computer monitors are additive, but color printers are subtractive. Instead of combining
light from monitor phosphors, printers coat paper with colored pigment which remove
specific colors from the illumination light. CMY is the subtractive color model that
corresponds to the additive RGB model. Cyan, magenta, and yellow are the color complements
of red, green, and blue. Due to the difficulties of manufacturing pigments that will
produce black when mixed together, a separate black ink is often used and is referred to
as K ('B' is already used for blue).
Color Map
See Look-Up-Table
Color Model
See Color Space
Color Space
A mathematical coordinate system
(space) for assigning numerical values to colors. There are many ways to define such
spaces, each with its own benefits and problems. See CMY & CMYK, IHS, HSL, HSV, Lab
(L*a*b*), RGB, YCrCb,YIQ.
Computer Output to Microfilm (COM): The
process of converting data to microfilm or microfiche. A COM device is a printer that
prints to microform instead of paper. It can supplement digital storage, such as an MO
jukebox.
Compression
An image processing method of saving
valuable disk and memory space by reducing the amount of space required to save a digital
image. The graphics data is rewritten so that it is represented by a smaller set of data.
Not to be confused with encoding. See also lossless and lossy compression.
Compression Ratio
The ratio of a file's uncompressed
size over its compressed size.
Convolution
An image processing operation which
can be used to spatially filter an image. A convolution is defined by a kernel which is a
matrix of fixed numbers. The size of the kernel, the numbers within it, and a single
normalizer value define the operation that will be applied to the image. The kernel is
applied to the image by placing the kernel over the image to be convolved and sliding it
around so that it is centered over every pixel in the original image. At each placement
the numbers (pixel values)from the original image are multiplied by the kernel number
which is currently aligned above it. The sum of all these products is tabulated and
divided by the kernel's normalizer. This result is placed into the new image at the
position of the kernels center. The kernel is then translated to the next pixel position
and the process repeats until all image pixels have been processed. As an example a 3x3
kernel holding all '1's with a normalizer of 9 performs a neighborhood averaging
operation. Each pixel in the new image is the average of its 9 neighbors from the original
coordinates. A pair of numbers which represent a specific location in a two-dimensional
plane such as an image or on a map. See also absolute, device, Cartesian, polar, relative,
screen, and world, coordinates.
Crop
An image processing method of
removing the region near the edge of the image, but keeping a central area.
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- D -
DDB (Device Dependent Bitmap)
A Window image specification which depends on the capabilities of
a specific graphics display controller. Since a DDB is matched to the current graphics
controller, it is fast and easy to display since large blocks of its memory need only be
copied to the controller. See also DIB.
Decompression
When an image or other digital data
set is compressed and stored, it is not usable until it is decompressed into it original
form.
Device Coordinates
The coordinates of the coordinate
system that describe the physical units by which the computer screen is defined.
Device Dependent (software)
Software that was written to work on
a specific set of hardware platforms. Since these routines make use of physical device
attributes, that may not exist or that may behave differently on other devices, they will
most often not work on other devices. See device independent and DIB.
Device Driver
A set of low-level software routines
which work with and control a specific hardware device. The names and functions are often
standardized across many similar devices. This allows higher level software to use the
hardware as a generic device. This frees the higher level software from dealing with the
particulars of the specific devices and allows device to be interchanged easily.
Device Independent
Software or data structures that
have been designed specifically to work with or on a wide set of hardware platforms. See
device dependent and DIB.
DIB (Device Independent Bitmap)
Windows defined image format
specification. It is called device independent because of its straightforward,
common-denominator, format. It has all the information that a basic digital image needs
and is laid out in a simple specification that is easy to get at. Its simplicity makes it
an ideal format for holding images that need to be shared by several programs. See also
DDB, and the book Programming Windows by Charles Petzold.
Dilation
See Morphology
Dithering
The method of using neighborhoods of
actual display pixels to represent one image intensity or color. This method allows low
intensity resolution display devices to simulate higher resolution images. For example, a
binary laser printer can use block patterns to display gray-scale images. See also
Half-tone.
Diazo: Diazo salts turn blue when exposed to ammonia. Diazo film is
used as a medium for storing the working copy of a silver hallide film. Diazo is not
recommended as and archival storage media, however it is quite durable and resistant to
scratching.
DLL (Dynamic Linked Library)
A compiled and linked collection of
computer functions that are not directly bound to an executable the way regular libraries
are. These libraries are linked at run-time by Windows. Since Windows is in charge of
managing(loading, linking, and removing) the DLLs, they are available to all executables
currently running. Thus, each executable can link to a commonly shared DLL saving memory
by avoiding redundant functions from co-existing. DLLs also allow a new level of
modularity by providing a means to modify and update executables without re-linking. All
that need be done is copy a new version of the DLL to the correct disk directory.
DPI (Dots per Inch)
Usually refers to the number of
printer dots that can be printed in one inch. Higher value printers will print sharper
images.
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- E -
Edge
In an image an edge is a region of contrast or color change. Edges
are often useful in machine vision since optical edges often mark the boundary of physical
objects.
Edge Detection
A method of isolating and locating
an optical edge in a given digital image.
Edge Map
The output of an image processing
filter that transforms an image into one where intensity represents a change in the
contrast (optical edge) of the original.
Eight (8)-bit Image
An image where each pixel has 8 bits
of information in it. An 8-bit pixel can take on one of 256 possible values. There
are two common types of 8-bit images: gray scale and indexed color. In gray-scale images
each pixel takes on one of 256 shades of gray and the shades are linearly
distributed from 0 (black) to 256 (white). An 8-bit gray-scale image doesn't require a
palette but may have one anyway. An indexed color image is always a palette image. Each
pixel is used as an index into the palette. Thus these images can have up to 256 different
colors in them at one time. This includes hues as well as shades. Indexed 8-bit images are
good for low color resolution images that will not need to be processed later on. They are
3x's smaller than full-color RGB images, but because the pixel values are not linear many
image processing algorithms cannot work with them. They must be promoted to 24 bit first.
Encoding
The manner in which data is stored
when uncompressed (binary, ASCII, etc.), how it's packed (e.g. 4-bit pixels may be packed
at a rate of two pixels per byte), and the unique set of symbols used to represent the
range of data items.
EPS (file format extension)
Encapsulated Postscript. Format originator: Adobe Systems, Inc.: 1585 Charleston Road
Mountain View, CA 94039
Equalize
An image processing algorithm which
redistributes the frequency of image pixel values so that any given continuous range of
values is equally represented. An equalized image has the same number of pixels in the
range from 10-20 as it does from 200-210. However, since digital images have quantized
intensity values, the range totals are rarely identical but usually close.
Erosion
See Morphology
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- F -
File Format
A specification for holding computer data in a disk file. The
format dictates what information is present in the file and how it is organized within it.
Filter
An image processing filter is a
transform which removes a specified quantity from an image. For instance a spatial filter
removes either high, medium or low spatial frequencies from an image.
Four (4)-bit Image
An image file format which allows
for 4-bits per pixel. Such an image can contain up to 16 (24)different colors or levels of
gray within it at one time.
Frame
A single picture, usually taken from
a collection of images such as in a movie or video stream.
Frame Buffer
A computer peripheral which is
dedicated to storing and sometimes manipulating digital images.
Frame Processes
A class of image processing
algorithms which operate on a single image at a time.
FX
See Special Effects.
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- G -
Gain & Level
Gain and level are image processing
terms which roughly correspond to the brightness and contrast control on a television. The
gain is the "contrast", and the level is the " brightness" . By
changing the level the entire range of pixel values are linearly shifted brighter or
darker. Gain on the other hand linearly stretches or shrinks the intensity range, thus
altering the contrast.
Gamma Correction
A non-linear function that is used
to correct the inherent non-linearities of cameras and monitors. The intensity of the
luminescent phosphor on the raster display when struck by an electron beam is non-linear.
Gamma correction is an adjustment to pixel intensity values that make up for this inherent
non-linearity.
Geometric Transform
A class of image processing
transforms which alter the location of pixels. This class includes rotates and warps.
GIF (file format extension)
Graphics Interchange File Format.
Format originator: CompuServe Inc. 500 Arlington Center Blvd./Columbus, OH 43220. Uses the
LZW compression created by Unisys, which requires special licensing. It is the same as the
LZW compression used in the TIFF file format, except that the bytes are reversed and the
string table is upside-down. All GIF files have a palette. Some GIF files can be
interlaced in that the raster lines can appear as every 4 lines, then every 8 lines, then
every other line. This is due to GIF files usually being received from a modem.
GUI (Graphical User Interface)
A computer-user interface which uses
graphical objects and a mouse for user interaction. Microsoft Windows is one such GUI.
Each program that runs under Windows follows similar conventions.
Graphics Library
A collection of software routines
which work on digital images. Such collections usually contain routines for drawing
various graphical objects such as lines, circles, and rectangles.
Gray Level
A shade of gray assigned to a pixel.
The shades are usually positive integer values taken from the gray-scale. In an 8-bit
image a gray level can have a value from 0 to 255.
Gray Scale
A range of gray levels. Zero is
usually black and higher numbers indicate brighter pixels.
Group III Fax
A CCITT standard for transmission of
facsimile data. It can compress black and white images using a combination of
differential, run length and Huffman coding.
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- H -
Half-tone
The reproduction of a
continuous-tone image on a device which does not directly support continuous output. This
is done by displaying or printing pattern of small dots which from a distance can simulate
the desired output color or intensity. These methods are used extensively in magazines and
newspapers.
Handle
A handle is used to reference a data
object. A handle is a type of pointer but it usually contains, internally, much more
information about the referenced object.
Histogram
A tabulation of pixel value
populations usually displayed as a bar chart where the x-axis represents all the possible
pixel values and the y-axis is the total image count of each given pixel value. That is, a
histogram counts how many pixels in the image have a given intensity value or range of
values. Each histogram intensity value or range of values is called a bin. Each bin
contains a positive number which represents the number of pixels in the image that fall
within the bin's range. A typical 8-bit gray-scale histogram contains256 bins. Each bin
has a range of a single intensity values. Thus, bin 0 contains the number of pixels in the
image that have a gray-scalevalue of 0 or black. Likewise, bin 255 contains the number of
white (255) pixels. When the collection of bins are sorted (0-255) and charted, the graph
displays the intensity distributions of all the images pixels.
HSL (Hue Saturation, and Lightness)
A method of describing any color as
a triplet of real values. The hue represents the color or wavelength of the color. It is
sometimes called tone and is what most people think of as color. The hue is taken from the
standard color wheel and is thus calibrated in degrees about the wheel. Saturation is the
depth of the color. It states how gray the color is. It is areal valued parameter from 0.0
to 1.0 with 0.0 indicating full gray and 1.0 representing pure hue. The lightness is how
black or white a color is. It also ranges from 0.0 to 1.0 but with 0.0 representing black
and 1.0 white. A lightness of 0.5 is pure hue.
HSV
Hue, Saturation, and Value.
Huffman Coding
A method of encoding symbols that
varies the length of the code in proportion to its information content. Groups of pixels
which appear frequently in a image are coded with fewer bits than those of lower
occurrence.
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- I -
IHS
Intensity, Hue, and Saturation
Indexed Color Image
An image where each pixel value is
used as an index to a palette for interpretation before it can be displayed. Such images
must, therefore, contain a palette which has been initialized specifically for a given
image. The pixel values are usually 8-bit and the palette 24-bit (8-red, 8-green, and
8-blue). See also eight-bit image.
Image Format
Refers to the specification under which an
image has been saved to disk or in which it resides in computer memory. There are many
commonly used digital image formats in use. Some of the most used are TIFF, DIB, GIF, and
JPEG. The image format specification dictates what image information is present and how it
is organized in memory. Many formats support various sub-formats or 'flavors'.
Image Processing
The general term "image processing"
refers to a computer discipline wherein digital images are the main data object. This type
of processing can be broken down into several sub-categories, including: compression,
image enhancement, image filtering, image distortion, image display and coloring, and
image editing. See also Machine Vision
Invert Intensity
An image processing operation where each
pixel, one at a time, is subtracted from the maximum pixel value allowed. This produced a
photographic negative of the original. For an 8-bit image the inverse function is: invert(
pix) = 255-pix; For an 8-bit RGB image the function is: invert( Rpix) =
255-Rpix;invert(Gpix) = 255-Gpix; invert(Bpix) = 255-Bpix;
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- J -
Jaggies
A term used to describe the visual appearance
of lines and shapes in raster pictures that results from drawing them using a grid of
insufficient spatial resolution.
JPEG (image compression)
Joint Photographic Experts Group. A
collaborative specification by the CCITT and the ISO for image compression. JPEG is
usually a lossy compression.
JPG (file format extension)
Format originator: Joint Photographics
Experts Group
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- K -
Kernel
A small matrix of pixels, usually no
bigger than 9x9, that is used as an operator during an image convolution. The kernel is
set prior to the convolution in a fashion that will emphasize a particular feature of the
image. Kernels are often used as spatial filters, each one tuned to a specific spatial
frequency that the convolution is intended to highlight. See also Convolution.
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- L -
Lempel Ziff Welch (data compression)
A dictionary based image compression method
with lossless performance which results in fair compression ratios. Most files can
be compressed around 2:1.
Level
See gain & level.
Look-Up-Table
A look-up-table or LUT is a continuous block
of computer memory that is initialized in such a fashion that it can be used to compute
the values of a function of one variable. The LUT is set up so that the functions variable
is used as an address or offset into the memory block. The value that resides at this
memory location becomes the functions output. Because the LUT values need only be
initialized once, LUTs are very useful for image processing because of their inherent high
speed. LUT[pixel_value] = f( pixel_value ) LUTs come in various widths, usually in units
of bits. An nxm bit LUT has 2n addresses or 256 stored values. Each value is 2m bits wide.
If the second dimension is left off it can be assumed to be equal to the first. In
gray-scale image processing LUTs are commonly 8x8, and the bit widths are usually assumed.
A linear LUT, sometimes called a NOP LUT or passthrough, is a LUT that has been
initialized to output the same values as the input. NOP_LUT[pixel_value ] = pixel_value.
See also Palette.
Lossless (image compression)
A method of image compression where there is
no loss in quality when the image is uncompressed. The uncompressed image is
mathematically identical to its original. Lossless compression is usually lower in
compression ratio than lossy compression.
Lossy (image compression)
A method of image compression where some
image quality is sacrificed in exchange for higher compression ratios. The amount of
quality degradation depends on the compression algorithm used and a user selected quality
variable.
LUT (Look-Up-Table)
See Look-Up-Table
LUT Transform
An image processing method that takes an
image and passes each pixel, one at a time, through a pre-set LUT. Thus, each new pixel is
a function of one and only one pixel from the original image and is arranged in the same
location. Any image processing algorithm that transforms a single pixel into another
single pixel, both from the same location, can be performed quickly using a LUT.
Square_root_LUT[ pixel_value ] = sqrt( pixel_value ) See Look-Up Table
LZW (data compression) Lempel Ziff Welch
See Lempel Ziff Welch
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- M -
Machine Vision
A sub-discipline of artificial intelligence
which uses video cameras or scanners to obtain information about a given environment.
Machine vision processes extract information from digital images about objects in the
image. This is the opposite of computer graphics which takes various data describing
objects in and produces an output image. Machine vision takes an image in and outputs some
level of description about the objects in it, (i.e. color, size, brightness). See also
Image Processing
Matrix Operation
See Neighborhood Process.
Median Filter
An image spatial filtering operation based on
an input pixel and its 8 neighbors. The resulting value is the median (5th from the sorted
values). A median filter is often used to reduce spike or speckling noise from a
gray-scale image. It has the advantage over convolution smoothing in that it better
preserves edges.
Microfiche: A 4" x 6" sheet of
film containing reduced images of up to 700 pages of documents in a grid pattern, usually
with a title that can be read without magnification. The number of images depends on the
level of magnification needed to view them full size. For example, at 42x reduction, you
can get 208 images on a fiche.
Microfiche, Jackets: A clear plastic
sheet with pockets that can hold tiny pieces of film containing documents. A jacket can
hold film pieces of different sizes, in any order, and it may or may not be full. A
microfilm scanner has to be intelligent enough to find the pieces and scan them
individually. The pieces often fall out, which is why it's a good idea to duplicate film
before handling or scanning it.
Microfilm: A film medium in tape-like
rolls, for recording reduced pages of documents sequentially. Common sizes include 16mm
and 35mm.
Microfilm reader/printer: A device that has a light source, a magnifying glass,
a screen and a printer. It lets you view and print microfilm images. You've probably seen
one in a library.
Microfilm scanner: A scanner that scans microfilm and fiche and converts film
images to digital images.
Microform: Umbrella term for microfiche and microfilm
Morphing
An imaging process where one image
is gradually transformed into a second image, where both images previously exist. The
result is a sequence of in-between images which when played sequentially, as in a film
loop show, give the appearance of the starting image being transformed to the second
image. Morphing is made up of a collection of image processing algorithms. The two major
groups are: warps and blends. Not to be confused with morphology.
Morphology
A neighborhood image processing algorithm
similar to image convolution except that Boolean logic is applied instead of arithmetic.
There are two types of morphology, binary and gray-scale. Both have similar operation but
are carried out differently because of the data width. The four major operations are;
erosion, dilation, opening, and closing. Erode - a filter which tends to make bright
objects smaller. Dilation - a filter which tends to make bright objects larger. Opening -
an erosion followed by a dilation. Closing - a dilation followed by an erosion. Not to be
confused with morphing.
MPEG (image compression)
Motion Pictures Experts Group. An
ISO specification of the compression of digital-broadcast quality full-motion video with
its sound track.
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- N -
Neighborhood Process
A class of image processing routines
which works on neighborhoods of pixels at a time. Each pixel in the new image is computed
as a function of the neighborhood of the pixel from the original pixel. The neighborhood
ID is defined by a kernel which is set once for each image to be processed. See also point
process.
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- O -
One (1) bit image
An image comprised of pixels that contain
only a single bit of information. Each pixel is either on or off. Normally, "on"
is white and "off" is black.
Opening
See morphology.
Overlay
An image or sub-image that can be placed over
a given image. The pixels from the original image are not altered but the overlay can be
viewed as if they had been. Usually used to place temporary text and annotation marks such
as arrows on a image.
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- P -
Packed Bits
A binary image is usually stored in computer
memory 8 pixels per byte. When this is the case each byte is referred to as being filled
with packed bits This saves space but makes reading and writing any individual pixel
somewhat harder since most computers cannot directly access memory in chunks smaller than
a byte.
Palette
A digital images palette is a collection of 3
look-up-tables or "LUT"s which are used to define a given pixels display color.
One LUT for red, one for green and one for blue. The number of entries in the LUTs depends
on the width in bits of the image's pixels. A palette image is one which requires its
palette in order to be displayed in a fashion which makes sense to the viewer. This is
often the case of color 8-bit images. Without a palette describing what color each pixel
is to be displayed with, such an image would most likely be displayed as randomly selected
noise. A gray-scale palette is one where each of the 3 LUTs are linear. That is, the
output is whatever is input to them. Since each color component (R, G, B) will be an equal
value, any pixels input to them will be displayed in a varying shade of gray. See also
Look-Up-Table
Pattern recognition
A sub-discipline of machine vision where
images are searched for specific patterns. Optical character recognition or
"OCR" is one type of pattern recognition, where images are searched for the
letters of the alphabet.
PCX (file format extension)
Format originator: ZSoft Corp.450 Franklin
Road Suite 100Marietta, GA 30067
Pixel
Short for the mostly obsolete term PIcture
(X) ELement. This is the most fundamental element of a digital image. A digital image is
made up of rows and columns of points of light. Each indivisible point of light is called
a pixel. Each pixel in an image is addressed by its column (x) and its row (y) usually
written as the coordinate pair (x,y). An 8-bit pixel can take on one of 256 values. A
24-bit pixel has 3, 8-bit components for each of the primary colors, red, green, and blue.
Point Process
A class of image processing transforms where
every pixel is taken, one at a time, from a provided image and mathematically transformed
into a new value with no input from any other pixel in the image. A point process is a
degenerative neighborhood process where the kernel is a matrix of pixels which is 1x1 (or
in other words, a single pixel.)
Polar Coordinates
An alternative to the usual Cartesian method
of addressing image pixels. Polar coordinates use the coordinate pair, angle and radius
from an origin instead of column and row.
Posterize
A special effect that decreases the number of
colors or gray-scales in an image. The default image pixel contains 256 levels of gray or
256 levels of red, green, and blue. Using this effect reduces these numbers.
Pseudocolor
A method of assigning color to ranges of a
gray-scale image's pixel values. Most often used to highlight subtle contrast gradients or
for visually quantifying pixel values. The applied color usually has no correspondence to
the original, physical imaged scene. The colors are used only as a guide or highlight.
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- Q -
- (empty)
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- R -
Raster
A term which for historical reasons is used
to describe a single row of a digital image. Thus a raster image is one that is made up of
rows of pixels. This is opposed to vector images, where an image is made up of a list of
polygon nodes. A raster is sometimes called a scan-line.relative coordinates Relative
coordinates refer to position, as identified as the distance from a local origin.
Render
The process of displaying an image. The final
and actual displayed image is said to have been rendered. The display
technology (software, monitor, etc.) will have a significant impact in the rendered image,
resulting in a discernable range of quality in images originating from the same file.
Resolution
There are two types of resolution in digital
images; spatial and intensity. Spatial resolution is the number of pixels per unit of
length along the x and y axis. Intensity resolution is the number of quantized levels that
a pixel can have.
RGB
Red, Green, Blue. A triplet of numeric values
which are used to describe a color.
RGBQUAD Red, Green, Blue, Quad.
A set of four numbers used to describe a
color. The forth number is always set to zero. By using this strange and seemingly
wasteful color value an efficient color LUT or palette can be created. It is more
efficient to use such a LUT because most computers find multiplying by 4 easier then by 3,
as would be the case in an RGB triplet.
ROI (Region Of Interest)
A region of interest or ROI is a
specification and date structure which allows for the definition of arbitrarily shaped
regions within a given image, often called sub-images. A ROI can be thought of as a place
holder which remembers a location within an image. ROIs can be one of several types, each
defined in a manor which makes sense for its type. At any one time a ROI is either a
rectangle (also called an AOI), square, circle, or a segment list. A rectangle is defined
by any two points in the image. From these two points one and only one rectangle can be
drawn. A square is defines by a single point and a single length. A circle by its center
and radius. A segment list is an arbitrary list of triplets (x,y,xlen); a single point and
a length to the right. Every point in an image is either inside or outside of a given ROI.
Most image processing functions in this package work only within a given ROI. The ROI can
encompass the entire image. See also AOI.
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- S -
Scan line
See Raster.
Screen Coordinates
Screen coordinates are those of the actual
graphics display controller. The origin is almost always at the upper left hand corner of
the display. See also Coordinates.
Segment
A contiguous section of a raster line.
Defined in physical coordinates by the triplet of its left-most point and length (x,y,
length).
Shear
A shear is image distortion which
most often occurs when a scanner is sampling am image and the image slides to either side
before the scan is complete. This has the effect of transforming squares into rhombuses.
Skew
The slant of an image that prevents it from being perfectly squared on the
page or screen
Special Effects
Any image processing transform which is
applied mostly for its artistic value.
Stretch Intensity
An image processing method which takes a
given image and assures that the intensity distribution fills the entire range of possible
values. An 8-bit image that has stretched will always have at least one pixel with a value
of zero and one of 255. The term comes from the before and after histogram of the given
image. A stretch operation will linearly stretch a histogram so that it ranges from the
minimum pixel value to the maximum pixel value.
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- T -
TGA (file format extension)
Format originator: Truevision, Inc.7340
Shadeland Station Indianapolis, IN 46255
TIFF (file format)
Tagged Image File Format.
TIF (file format extension)
Format originator: Aldus Corp and Microsoft
Corp; 411 First Ave South Seattle, WA 98104; 16011 NE 36th Way Redmond, WA
98073
Thumbnail
A small copy of an image. Usually used to
display many images on the screen at once.
Transform
An algorithm which takes an image, alters it,
and outputs a new image. Sometimes written as 'xform'. See also Point transform,
Neighborhood transform, and Geometric transform.
Triplet
Three numbers which when used together
represent a single quantity or location such as RGB or (x,y,z).
Twenty-Four (24)- bit image
A 24-bit image contains pixels which are made
up of RGB triplets.
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- U -
- (empty)
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- V -
Video Stream
A sequence of still images that are
transmitted and displayed in synchronous order given the appearance of live motion.
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- W -
Warp
A geometric image processing routine which
distorts an image by spatially compressing and stretching regions.
WMF (file format extension)
Format originator: Microsoft Corp16011 NE
36th Way Redmond, WA 98073
World Coordinates
The real valued coordinates that make sense
for the object, treating it as if it really exists. Thus, the world coordinates of a house
on a map would be in miles or longitude and latitude. This is the opposite of screen,
device or model coordinates.
WPG (file format extension)
Format originator: Word Perfect Corp
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- X -
(x,y)
A mathematical method for referring to a
pixel from a digital image. Since most digital images are maintained as a Cartesian matrix
of pixels, each pixel has a unique address which can be described as an x or horizontal
displacement from the origin and a y or vertical displacement from the origin. See also
coordinates.
Xform
Short-hand for transform.
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- Y -
YIQ (Y)luminance, (I), (Q).
YIQ is the color model used for U.S.
commercial television. It was designed to be backwards compatible with the old black and
white television sets. "Y" or luminance is a weighted average of the red, green,
and blue which give more weight to red and green than to blue. The I and Q contain the
color components. Together they are called the chromoticity.
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- Z -
-
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Revised: Last Update: Monday, 22-Jan-2007 15:03:14 EST.
Copyright © 1998 by AMS Imaging.
Some components (C) Northern Micrographics
All trademarks or product names mentioned herein are the property of their respective
owners.
Created: September 14, 1996
Copyright© AMS 1996-2008
