Glossary

LabView NI Vision

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Glossary

A

AIPD National Instruments internal image file format used for saving complex and HSL images and calibration information associated with an image. AIPD images have the file extension APD.
alignment The process by which a machine vision application determines the location, orientation, and scale of a part being inspected.
area threshold Detects objects based on their size, which can fall within a user-specified range.
arithmetic operators The image operations multiply, divide, add, subtract, and remainder.
asynchronous Property of a function or operation that begins an operation and returns control to the program before the completion or termination of the operation.
auto-median function A function that uses dual combinations of opening and closing operations to smooth the boundaries of objects.

B

barycenter The barycenter of a range of an image's grayscale values is the grayscale value representing the centroid of that range in the image histogram.
binary image An image containing objects usually represented with a pixel intensity of 1(or 255) and the background of 0.
binary morphology Functions that perform morphological operations on a binary image.
blob Binary large object. A particle, or object, present in a binary image.
blurring Reduces the amount of detail in an image. Blurring commonly occurs because the camera is out of focus. You can blur an image intentionally by applying a lowpass frequency filter.
BMP Bitmap. Image file format commonly used for 8-bit and color images. BMP images have the file extension BMP.
border function Removes objects (or particles) that touch the image border in a binary image.

C

caliper Finds edge pairs along a specified path in the image. This function performs an edge extraction and then finds edge pairs based on specified criteria such as the distance between the leading and trailing edges, edge contrasts, and so forth.
cell A single module that encodes one bit of data in a 2D barcode.
CIE L*a*b* Color encoding scheme that classifies colors according to the human vision system by mimicking the logarithmic response of the eye.
CIE XYZ Color encoding scheme that classifies colors according to the human vision system.
circle function Detects circular objects in a binary image.
class A category representing a collection of similar samples.
classification An operation that assigns samples to classes based on predefined features.
classification accuracy Probability that a sample is classified into the class to which it belongs.
classification confidence Degree of certainty that a sample is assigned to one class instead of other classes. See also class and sample.
classification predictive value Probability that a sample classified into a given class belongs to that class.
classifier A function or VI that assigns a sample to a class.
closed contour An ROI that describes an inclusive area in an image. Types of closed contours include the following: Rectangle, Oval, Polygon, Freehand Region, Annulus, and Rotated Rectangle.
closing A dilation followed by an erosion. A closing fills small holes in objects and smooths the boundaries of objects.
CLUT Color lookup table. Table for converting the value of a pixel in an image into a red, green, and blue (RGB) intensity.
code word Numeric value of the printed bar/space pattern in a 1D or 2D barcode.
color images Images containing color information, usually encoded in the RGB form.
complex images Save information obtained from the FFT of an image. The complex numbers that compose the FFT plane are encoded in 64-bit floating-point values: 32 bits for the real part and 32 bits for the imaginary part.
connectivity Defines which of the surrounding pixels of a given pixel constitute its neighborhood.
connectivity-4 Only pixels adjacent in the horizontal and vertical directions are considered neighbors.
connectivity-8 All adjacent pixels are considered as neighbors.
convex hull function Computes the convex hulls of objects in a binary image.
convolution See linear filter.
convolution kernel 2D matrices (or templates) used to represent the filter in the filtering process. The contents of these kernels are a discrete two-dimensional representation of the impulse response of the filter that they represent.
curve extraction The process of finding curves or connected edge points in a grayscale image. Curves usually represent the boundaries of objects in the image.

D

Danielsson function Similar to the distance functions, but with more accurate results.
densitometry Determination of optical or photographic density.
density function For each gray level in a linear histogram, it gives the number of pixels in the image that have the same gray level.
device Plug-in data acquisition board that can contain multiple channels and conversion devices.
differentiation filter Extracts the contours (edge detection) in gray level.
digital image An image f (x, y) that has been converted into a discrete number of pixels. Both spatial coordinates and brightness are specified.
dilation Increases the size of an object along its boundary and removes tiny holes in the object.
distance calibration Determination of the physical dimensions of a pixel by defining the physical dimensions of a line in the image.
distance function Assigns, to each pixel in an object, a gray-level value equal to its shortest Euclidean distance from the border of the object.

E

edge Defined by a sharp change (transition) in the pixel intensities in an image or along an array of pixels.
edge contrast The difference between the average pixel intensity before and the average pixel intensity after the edge.
edge hysteresis The difference in threshold levels between a rising and a falling edge.
edge steepness The number of pixels that correspond to the slope or transition area of an edge.
entropy A measure of the randomness in an image. An image with high entropy contains more pixel value variation than an image with low entropy.
equalize function See histogram equalization.
erasure Missing or undecodable codeword at a known position in a 2D barcode.
erosion Reduces the size of an object along its boundary and eliminates isolated points in the image.
exponential and gamma corrections Expand the high gray-level information in an image while suppressing low gray-level information.
exponential function Decreases the brightness and increases the contrast in bright regions of an image and decreases contrast in dark regions.

F

feature A measurement from or attribute of a sample.
feature extraction An operation that computes features of a sample.
feature vector A 1D array in which each element represents a different feature of a sample.
FFT Fast Fourier Transform. A method used to compute the Fourier Transform of an image.
fiducial A reference pattern on a part that helps a machine vision application find the part's location and orientation in an image.
Fourier spectrum The magnitude information of the Fourier Transform of an image.
Fourier Transform Transforms an image from the spatial domain to the frequency domain.
frequency filters Counterparts of spatial filters in the frequency domain. For images, frequency information is in the form of spatial frequency.

G

gauging Measurement of an object or distances between objects.
Gaussian filter A filter similar to the smoothing filter, but using a Gaussian kernel in the filter operation. The blurring in a Gaussian filter is more gentle than a smoothing filter.
geometric matching The technique used to locate a grayscale template that is characterized by distinct geometric or shape information within a grayscale image.
geometric features The information extracted from a grayscale template that is used to locate the template in the target image. Geometric features in an image range from low-level features, such as edges or curves detected in the image, to high-level features, such as the geometric shapes made by curves in the image.
golden template An image containing an ideal representation of an object under inspection.
gradient convolution filter See gradient filter.
gradient filter Extracts the contours (edge detection) in gray-level values. Gradient filters include the Prewitt and Sobel filters.
gray level The brightness of a point (pixel) in an image.
gray-level dilation Increases the brightness of pixels in an image that are surrounded by other pixels with a higher intensity.
gray-level erosion Reduces the brightness of pixels in an image that are surrounded by other pixels with a lower intensity.
gray-level images Images with monochrome information.
gray-level morphology Functions that perform morphological operations on a gray-level image.

H

highpass attenuation Applies a linear attenuation to the frequencies in an image, with no attenuation at the highest frequency and full attenuation at the lowest frequency.
highpass FFT filter Removes or attenuates low frequencies present in the FFT domain of an image.
highpass filter Emphasizes the intensity variations in an image, detects edges (or object boundaries), and enhances fine details in an image.
highpass frequency filter Attenuates or removes (truncates) low frequencies present in the frequency domain of the image. A highpass frequency filter suppresses information related to slow variations of light intensities in the spatial image.
highpass truncation Removes all frequencies below a certain frequency.
histogram Indicates the quantitative distribution of the pixels of an image per gray-level value.
histogram equalization Transforms the gray-level values of the pixels of an image to occupy the entire range (0 to 255 in an 8-bit image) of the histogram, increasing the contrast of the image.
histogram inversion Finds the photometric negative of an image. The histogram of a reversed image is equal to the original histogram flipped horizontally around the center of the histogram.
hit-miss function Locates objects in the image similar to the pattern defined in the structuring element.
hole filling function Fills all holes in objects that are present in a binary image.
HSI Color encoding scheme in Hue, Saturation, and, Intensity.
HSL Color encoding scheme using Hue, Saturation, and Luminance information where each image in the pixel is encoded using 32-bits: 8 bits for hue, 8 bits for saturation, 8 bits for luminance, and 8 unused bits.
HSV Color encoding scheme in Hue, Saturation, and Value.

I

image A two-dimensional light intensity function f (x, y), where, x and y denote spatial coordinates and the value f at any point (x, y) is proportional to the brightness at that point.
image file A file containing image information and data.
image processing Encompasses various processes and analysis functions that you can apply to an image.
image understanding A technique that interprets the content of the image at a symbolic level rather than a pixel level.
image visualization The presentation (display) of an image (image data) to the user.
inner gradient Finds the inner boundary of objects.
inspection The process by which parts are tested for simple defects such as missing parts or cracks on part surfaces.
inspection functions Detects specific features in an image, including edges, peaks, and rotational shifts.
intensity calibration Assigning user-defined quantities such as optical densities or concentrations to the gray-level values in an image.
intensity profile The gray-level distribution of the pixels along an ROI in an image.
intensity range Defines the range of gray-level values in an object of an image.
intensity threshold Characterizes an object based on the range of gray-level values in the object. If the intensity range of the object falls within the user-specified range, it is considered an object; otherwise it is considered part of the background.
interpolation The technique used to find values between known values when resampling an image or array of pixels.
invariant feature A feature vector that is invariant to variations such as the scale, rotation, and mirror symmetry of samples.

J

JPEG Joint Photographic Experts Group. Image file format for storing 8-bit and color images with lossy compression. JPEG images have the file extension JPG.
JPEG2000 An image file format for storing 8-bit, 16-bit, or color images with either lossy or lossless compression. JPEG2000 images have the file extension JP2.

L

labeling A morphology operation that identifies each object in a binary image and assigns a unique pixel value to all the pixels in an object. This process is useful for identifying the number of objects in the image and giving each object a unique pixel intensity.
Laplacian filter Extracts the contours of objects in the image by highlighting the variation of light intensity surrounding a pixel.
line gauge Measures the distance between selected edges with high-precision subpixel accuracy along a line in an image. For example, this function can be used to measure distances between points and edges and vice versa. This function also can step and repeat its measurements across the image.
line profile Represents the gray-level distribution along a line of pixels in an image.
linear filter A special algorithm that calculates the value of a pixel based on its own pixel value as well as the pixel values of its neighbors. The sum of this calculation is divided by the sum of the elements in the matrix to obtain a new pixel value.
local threshold A method of image segmentation that categorizes a pixel as part of a particle or the background based on the intensity statistics of the particle's neighboring pixels.
logarithmic and inverse gamma corrections Expand low gray-level information in an image while compressing information from the high gray-level ranges.
logarithmic function Increases the brightness and contrast in dark regions of an image and decreases the contrast in bright regions of the image.
logic operators The image operations AND, NAND, OR, NOR, XOR, XNOR, difference, mask, mean, max, and min.
lossless compression Compression in which the decompressed image is identical to the original image.
lossy compression Compression in which the decompressed image is visually similar but not identical to the original image.
lowpass attenuation Applies a linear attenuation to the frequencies in an image, with no attenuation at the lowest frequency and full attenuation at the highest frequency.
lowpass compression Removes or attenuates high frequencies present in the FFT domain of an image.
lowpass FFT filter Attenuates intensity variations in an image. You can use these filters to smooth an image by eliminating fine details and blurring edges.
lowpass frequency filter Attenuates high frequencies present in the frequency domain of the image. A lowpass frequency filter suppresses information related to fast variations of light intensities in the spatial image.
lowpass truncation Removes all frequency information above a certain frequency.
L-skeleton function Uses an L-shaped structuring element in the Skeleton function.
LUT Lookup table. Table containing values used to transform the gray-level values of an image. For each gray-level value in the image, the corresponding new value is obtained from the lookup table.

M

machine vision application An inspection or measurement application that uses images acquired from a 2D sensor (typically a CCD camera) to help with inspection or measurement.
mask Isolates parts of an image for further processing.
mask FFT filter Removes frequencies contained in a mask (range) specified by the user.
mask image An image containing a value of 1 and values of 0. Pixels in the source image with a corresponding mask image value of 1 are processed, while the others are left unchanged.
match score A number ranging from 0 to 1000 that indicates how closely an acquired image matches the template image. A match score of 1000 indicates a perfect match. A match score of 0 indicates no match.
median filter A lowpass filter that assigns to each pixel the median value of its neighbors. This filter effectively removes isolated pixels without blurring the contours of objects.
MMX Multimedia Extensions. Intel chip-based technology that allows parallel operations on integers, which results in accelerated processing of 8-bit images.
morphological transformations Extract and alter the structure of objects in an image. You can use these transformations for expanding (dilating) or reducing (eroding) objects, filling holes, closing inclusions, or smoothing borders. They mainly are used to delineate objects and prepare them for quantitative inspection analysis.
M-skeleton Uses an M-shaped structuring element in the skeleton function.
multiple template matching The technique used to simultaneously locate multiple grayscale templates within a grayscale image.

N

neighbor A pixel whose value affects the values of nearby pixels when an image is processed. The neighbors of a pixel are usually defined by a kernel.
neighborhood operations Operations on a point in an image that take into consideration the values of the pixels neighboring that point.
nonlinear filter Replaces each pixel value with a nonlinear function of its surrounding pixels.
nonlinear gradient filter A highpass edge-extraction filter that favors vertical edges.
nonlinear Prewitt filter A highpass edge-extraction filter that favors horizontal and vertical edges in an image.
nonlinear Sobel filter A highpass edge-extraction filter that favors horizontal and vertical edges in an image.
Nth order filter Filters an image using a nonlinear filter. This filter orders (or classifies) the pixel values surrounding the pixel being processed. The pixel being processed is set to the Nth pixel value, where N is the order of the filter.

O

open contour An ROI that describes a point or area in an image. Types of open contours include the following: Point, Line, Broken Line, and Free Hand Line.
opening An erosion followed by a dilation. An opening removes small objects and smooths boundaries of objects in the image.
operators Allow masking, combination, and comparison of images. You can use arithmetic and logic operators in NI Vision.
occlusion invariant matching A geometric matching technique in which the reference pattern can be partially obscured in the target image.
OCR Opticle character recognition. The process of analyzing an image to detect and recognize characters/text in the image.
OCV Optical character verification. A machine vision application that inspects the quality of printed characters.
optical representation Contains the low-frequency information at the center and the high-frequency frequency information at the corners of an FFT-transformed image.
outer gradient Finds the outer boundary of objects.

P

palette The gradation of colors used to display an image on screen, usually defined by a color lookup table.
particle A connected region or grouping of pixels in an image in which all pixels have the same intensity level.
particle classifier A classifier that classifies particles. See also classifier and particle.
pattern matching The technique used to locate quickly known reference patterns or fiducials in an image.
picture element An element of a digital image.
pixel Picture element.
pixel calibration Directly calibrating the physical dimensions of a pixel in an image.
pixel depth The number of bits used to represent the gray level of a pixel.
PNG Portable Network Graphic. Image file format for storing 8-bit, 16-bit, and color images with lossless compression.
Power 1/Y function Similar to a logarithmic function but with a weaker effect.
Power Y function See exponential function.
Prewitt filter Extracts the contours (edge detection) in gray-level values using a 3 × 3 filter kernel.
probability function Defines the probability that a pixel in an image has a certain gray-level value.
proper-closing A finite combination of successive closing and opening operations that you can use to fill small holes and smooth the boundaries of objects.
proper-opening A finite combination of successive opening and closing operations that you can use to remove small particles and smooth the boundaries of objects.
pyramidal matching A technique used to increase the speed of a pattern matching algorithm by matching subsampled versions of the image and the reference pattern.

Q

quantitative analysis Obtaining various measurements of objects in an image.

R

Reverse function Inverts the pixel values in an image, producing a photometric negative of the image.
RGB Color encoding scheme using red, green and blue (RGB) color information where each pixel in the color image is encoded using 32 bits: 8 bits for red, 8 bits for green, 8 bits for blue, and 8 bits for the alpha value (unused).
RGB U64 Color encoding scheme using red, green, and blue (RGB) color information where each pixel in the color image is encoded using 64 bits: 16 bits for red, 16 bits for green, 16 bits for blue, and 16 bits for the alpha value (unused).
Roberts filter Extracts the contours (edge detection) in gray level, favoring diagonal edges.
ROI Region of interest. An area of the image that is graphically selected from a window displaying the image. This area can be used to focus further processing. This region can also be defined programmatically.
rotation-invariant matching A pattern matching technique in which the reference pattern can be at any orientation in the test image.
rotational shift The amount by which one image is rotated with respect to a reference image. This rotation is computed with respect to the center of the image.

S

sample An object in an image that you want to classify.
scale-invariant matching A pattern matching technique in which the reference pattern can be any size in the test image.
segmentation function Fully partitions a labeled binary image into non-overlapping segments, with each segment containing a unique object.
separation function Separates objects that touch each other by narrow isthmuses.
shape descriptor A feature vector that describes the shape of a sample. See also feature vector and particle analysis.
shape matching Finds objects in an image whose shape matches the shape of the object specified by a template. The matching process is invariant to rotation and can be set to be invariant to the scale of the objects.
shift-invariant matching A pattern matching technique in which the reference pattern can be located anywhere in the test image but cannot be rotated or scaled.
Sigma filter A highpass filter that outlines edges.
skeleton function Applies a succession of thinning operations to an object until its width becomes one pixel.
skiz Obtains lines in an image that separate each object from the others and are equidistant from the objects that they separate.
smoothing filter Blurs an image by attenuating variations of light intensity in the neighborhood of a pixel.
Sobel filter Extracts the contours (edge detection) in gray-level values using a 3 × 3 filter kernel.
spatial calibration Assigning physical dimensions to the area of a pixel in an image.
spatial filters Alter the intensity of a pixel with respect to variations in intensities of its neighboring pixels. You can use these filters for edge detection, image enhancement, noise reduction, smoothing, and so forth.
spatial resolution The number of pixels in an image, in terms of the number of rows and columns in the image.
Square function See exponential function.
Square Root function See logarithmic function.
standard representation Contains the low-frequency information at the corners and high-frequency information at the center of an FFT-transformed image.
structuring element A binary mask used in most morphological operations. A structuring element is used to determine which neighboring pixels contribute in the operation.
subpixel analysis Used to find the location of the edge coordinates or pattern matching results in terms of fractions of a pixel.
substitution error Erroneously decoded codeword at an unknown position in a 2D barcode.
synchronous Property or operation that begins an operation and returns control to the program only when the operation is complete.
syntax Set of rules to which statements must conform in a particular programming language.

T

thickening Alters the shape of objects by adding parts to the object that match the pattern specified in the structuring element.
thinning Alters the shape of objects by eliminating parts of the object that match the pattern specified in the structuring element.
threshold Separates objects from the background by assigning all pixels with intensities within a specified range to the object and the rest of the pixels to the background. In the resulting binary image, objects are represented with a pixel intensity of 255 and the background is set to 0.
threshold interval Two parameters, the lower threshold gray-level value and the upper threshold gray-level value.
TIFF Tagged Image File Format. Image format commonly used for encoding 8-bit and color images. TIFF images have the file extension TIF.
truth table A table associated with a logic operator that describes the rules used for that operation.

V

virtual corner A corner that would be created if two non-intersecting lines are extended until they intersect.

W

watershed transform A method of image segmentation that partitions an image based on the topographic surface of the image. The image is separated into non-overlapping segments with each segment containing a unique particle.
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