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Topic: Edge detection

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Canny

Sobel

Roberts Cross

Digital image processing

Noise reduction

Chroma subsampling

Transform coding

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2D computer graphics

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Quantization (signal processing)

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	Edge Detection
		Edges are scale-dependent and an edge may contain other edges, but at a certain scale, an edge still has no width.
		As a user of an edge detector, one should not expect the software to automatically detect all the edge he or she wants and nothing more, because a program can not possibly know what level of details the experimenter has in mind.
		However, if the edge he has in mind is not as obvious to the program as some other features he does not want detect, he will get the other "noise" before the desired edge is detected.
	www.prettyview.com /edge (811 words)

	Edge Detection
		Edge detection is a problem of fundamental importance in image analysis.
		In typical images, edges characterize object boundaries and are therefore useful for segmentation, registration, and identification of objects in a scene.
		The edges are identified by the location of zero crossings (recall that the second derivative changes sign in the vicinity of maxima of the first derivative).
	library.wolfram.com /examples/edgedetection (998 words)

	Edge detection using dual trans-impedance amplifier - Patent 4698528
		The output of the edge detection circuit is connected to a dual threshold comparator having a positive threshold for detecting valid positive differentiated pulses and a negative threshold for detecting valid negative differentiated pulses.
		This increases the effective gain of the edge detection circuit, thereby enabling the edge of the input waveform to produce a negative excursion 2 of the detected edge waveform B as shown in FIG.
		The detected edge waveform B makes an excursion to a negative amplitude at 3 and stays at that amplitude for a characteristic duration determined by the frequency response of the circuit components resistors R2, R4 and other elements in the circuit.
	www.freepatentsonline.com /4698528.html (2108 words)

	Canny Edge Detection Tutorial
		The Canny edge detection algorithm is known to many as the optimal edge detector.
		Whenever the gradient in the x direction is equal to zero, the edge direction has to be equal to 90 degrees or 0 degrees, depending on what the value of the gradient in the y-direction is equal to.
		Nonmaximum suppression is used to trace along the edge in the edge direction and suppress any pixel value (sets it equal to 0) that is not considered to be an edge.
	www.pages.drexel.edu /~weg22/can_tut.html (1241 words)

	Edge Detection
		The strongest negative edge transitions were then detected with a threshold operation, in which the pixels of B that were less than a threshold b were detected.
		The strongest positive edge transitions were then detected with a threshold operation, in which the pixels of B that were greater than a threshold a were detected.
		The edges detected from the combined gradient image with a threshold set at a=145 is shown in Figure 8.
	www.cis.rit.edu /people/faculty/rhody/EdgeDetection.htm (1235 words)

	Edge Detection Tutorial
		Edges in images are areas with strong intensity contrasts — a jump in intensity from one pixel to the next.
		This method of locating an edge is characteristic of the “gradient filter” family of edge detection filters and includes the Sobel method.
		The Sobel edge detector uses a pair of 3x3 convolution masks, one estimating the gradient in the x-direction (columns) and the other estimating the gradient in the y-direction (rows).
	www.pages.drexel.edu /~weg22/edge.html (927 words)

	MTRUBS - Edge Detection Algorithms
		Edge detection is an important concept, both in the area of image processing and in the area of object recognition.
		Edge detection is the process of determining where the boundaries of objects fall within an image.
		Sobel edge detection is similar to the Roberts Cross approach in that both use two kernels to convolve an image, where the second kernel is simply a 90 degree rotation of the first kernel [1].
	www.ccs.neu.edu /home/mtrubs/html/EdgeDetection.html (3819 words)

	Edge detection
		In this example, edges are considered to be the maxima of the gradient modulus in the direction of the gradient.
		The edge detection is performed in 2D on each sagittal slice, and the results are collected to form a 3D volume.
		Edge detection with a recursive approximation of the Gaussian
	www-sop.inria.fr /epidaure/personnel/malandain/segment/edges.html (283 words)

	Raster to Vector Conversion -- Vectorization
		The Edge Detection methods look for edges of objects and are useful for images with solid regions whose outlines need to be vectorized.
		The Inner Edge Detection is most practical for bi-level images, mostly scanned drawings, as opposed to the Canny method which produces best results vectorizing color images.
		On the other hand, the Canny edge detection method looks also for edges of objects; however, this method is most useful for images with solid color regions where the outlines of the largest regions in a particular area of the image are vectorized.
	www.parallax69software.com /vectorize.htm (1447 words)

	Edge and line detection in low level analysis
		Edge detection and line extraction are important and critical components in an image understanding system, the result of the extraction being the basis of the high level processes.
		The length of the arrow is proportional to the intensity of the edge.
		Faint edge lines, such as the limit of the quiet zone at the right and top of the symbol, are detected although these were not detected as continuous long lines.
	www.dunwich.org /baptiste/sic/ecms/ecpublis.html (2740 words)

	Edge Detection Using Zero-Crossings (Site not responding. Last check: )
		Edge extraction is an important part of the transformation from Image to Primal Sketch.
		Edges are the places in an image where intensity changes rapidly from dark to light (or vice-versa).
		Edges can be extracted from an image by convolving the image with the Laplacian of a Gaussian.
	cogsci.ucsd.edu /~tkmarks/marr/Vision/Edge_Detection_Using_Zero-Cros/edge_detection_using_zero-cros.html (177 words)

	EDGE / LINE DETECTION (Site not responding. Last check: )
		In this edge detection method the assumption is that edges are the pixels with a high gradient.
		The basic idea of edge detection operators is based on comparison of the brightness values of pixels with their neighbors.
		The detection criterion is the presence of a zero crossing in the second derivative with the corresponding large peak in the first derivative.
	ari.cankaya.edu.tr /~reza/ImLab4.htm (2619 words)

	3D Visualization For Blood Cells Analysis Versus Edge Detection
		Edge detection is essentially the operation of detection significantly local changes in image.
		In blood cell image detection, the task is usually split into two stages one is image enhancement, with the purpose of reducing noise and clear view and the other is detection of blood cell data.
		Edge detection is often used as a basic method for diagnosis of blood disorder.
	www.ispub.com /ostia/index.php?xmlFilePath=journals/ijmt/vol1n2/3d.xml (2116 words)

	Edge detection by Laplacian
		Another large group of edge detection techniques are the techniques that use second-order derivative operators, particularly Laplacian.
		Edges may thus be approximated by the pixels with relatively large absolute value of the Laplacian.
		The main disadvantage of such approach is that it usually detects two adjacent edges for every edge in the image.
	www.cs.technion.ac.il /Labs/Isl/Project/Projects_done/VisionClasses/Vision/Edge_Detection/node5.html (435 words)

	Classical Feature Detection
		Edges often occur at points where there is a large variation in the luminance values in an image, and consequently they often indicate the edges, or occluding boundaries, of the objects in a scene.
		Most edge detection methods work on the assumption that an edge occurs where there is a discontinuity in the intensity function or a very steep intensity gradient in the image.
		are respectively the detected edges, the ideal edges, the distance between the actual and the ideal edges, and a design constant used to penalise displaced edges.
	homepages.inf.ed.ac.uk /rbf/CVonline/LOCAL_COPIES/OWENS/LECT6/node2.html (2150 words)

	Image Processing Lab - Edge Detection
		The second derivative is positive for the part of the transition associated with the dark side of the edge and negative for the transition associated with the light side of the edge.
		Thus the magnitude of the first derivative can be used to detect the presence of an edge in the image and the sign of the second derivative can be used to detect whether a pixel lies on the light or dark side of the edge.
		In edge detection the important quantity is the magnitude of this vector which is usually referred to as the "gradient." The gradient is the maximum rate of increase of f(x,y) per unit distance in the direction of the gradient vector.
	www.eng.iastate.edu /ee424/labs/iplab/part3_spec.html (752 words)

	Edge Detection (Site not responding. Last check: )
		In most edge detection algorithms such as Canny [Canny 83, 86], Shen-Castan [Shen and Castan 92], the three components are used.
		The two dimensional edge would be the magnitude of the gradient of the grayscale.
		The output from the edge detection scheme is ASCII PGM format image, where each pixel is given the value 0 (for those NOT belonging to edge) or 255 (for those belonging to an edge).
	www.cs.kent.edu /~nochiai/ThesisD/edge_detect.html (459 words)

	Canny edge detector (Canny filter) for image processing and computer vision - Model parameters (Site not responding. Last check: )
		The basic algorithm deployed for edge detection is that of J. Canny [1].
		Canny edge detection starts with linear filtering to compute the gradient of the image intensity distribution function and ends with thinning and thresholding to obtain a binary map of edges.
		More precisely, in the case of isotropic suppression, the contourness of an edge point is computed as 1 - mw / m, where m is the value of the gradient magnitude and mw is the value of convolution of the gradient magnitude field with the inhibition kernel w in the concerned point.
	matlabserver.cs.rug.nl /cannyedgedetectionweb/web/cannydetection_params.html (1335 words)

	Blob Analysis and Edge Detection In the Real World
		While blob analysis concerns itself with regions of connected pixels based on their pixel value, edge detection is established from the intensity of transitions in an image.
		Edges are determined from differential analysis and extracted by analyzing intensity transitions in images.
		An edge element (edgel) is located at the maximum value of the gradient magnitude over adjacent pixels in the direction defined by the gradient vector.
	www.evaluationengineering.com /archive/articles/0806/0806blob_analysis.asp (1996 words)

	Edge and Line Detection
		Edge detection by the LoG operator is due to Marr and Hildreth [1].
		Many of the detected edges correspond to small details in an image and need to be removed.
		The edge detection methods described so far use intensity differences as the metric to detect edges.
	www.imgfsr.com /ifsr_is_ed.html (713 words)

	Edge Detection Examples
		Edge detection uses the difference in color between the background color and the forground color in your banner.
		If you blur your banner there will be a "softer" edge to detect and you can create interesting effects mixing edge detection and blur.
		Since edge detection uses the difference of the forground and background, it makes sense to only use a Background Color of Black, and selecting the color you want in your banner as the Forground Color.
	www.coder.com /creations/banner/examples/edge.html (352 words)

	Optimal Edge-Based Shape Detection (Site not responding. Last check: )
		Edge-based shape detection methods all suffer from the same problem: loss of information at the edge detection stage and the difficulty of statistical performance analysis.
		Observe that the detection performance of the DODE operator is very slightly poorer than that of the DOG operator, for the same scale of the width.
		If we define shape detection as the process of identifying the intensity changes along the shape boundary, we can claim that our scheme is optimal; convolving the ideal image with the shape operator is equivalent to computing intensity gradients after optimal smoothing.
	www.cfar.umd.edu /~hankyu/shape_html (2034 words)

	Using Edge Detection in Machine Vision Gauging Applications- Developer Zone - National Instruments
		The contrast parameter specifies the threshold for the contrast of the edge.
		For an edge to be located in the line profile, using the filter width and steepness settings, the edge contrast between foreground and background must be greater than the contrast setting.
		An edge along the line profile is defined by the level of contrast between background and foreground and the slope of the transition.
	zone.ni.com /devzone/cda/tut/p/id/4536 (3143 words)

	Edge Detector Comparison
		In a newer phase of work on the comparison of edge detection algorithms, five edge detectors were evaluated.
		These images, and the edges detected in them by five edge detection algorithms are being provided for others to use.
		The best edge images were determined in two different ways; by finding the best parameters to use for the set of images (fixed parameters) and by adapting the parameters to each individual image (adapted parameters).
	marathon.csee.usf.edu /edge/edge_detection.html (392 words)

	Edge Detection in Images Overview (Site not responding. Last check: )
		Edges characterize object boundaries and are therefore useful for segmentation, registration, and identification of objects.
		Edges in an image are pixel locations with abrupt changes in gray levels.
		Therefore, one edge detection technique is to measure the gradient of f in a particular location.
	www.ee.ucla.edu /~dsplab/edi/over.html (439 words)

	Edge Detection - IGEM
		Edge Detection algorithms make it possible to find those changes and to draw a line corresponding to existing contours.
		But there seems to be a cool reward: Because difussion coefficients are depending on temperature, one could imagine to control the resolution of the edge detection device by setting the temperature of the culture medium.
		a sharp edge), the bacteria on the left will produce no or little A, whereas the bacteria on the right hand side produce much A. The concentration of A will of course not have a sharp edge on the boundary, but will be blurred due to diffusion.
	parts2.mit.edu /wiki/index.php/Edge_Detection (707 words)

	Feature Detectors - Sobel Edge Detector
		Natural edges in images often lead to lines in the output image that are several pixels wide due to the smoothing effect of the Sobel operator.
		We can see that the noise has increased during the edge detection and it is no longer possible to find a threshold which removes all noise pixels and at the same time retains the edges of the objects.
		A related operator is the Prewitt gradient edge detector (not to be confused with the Prewitt compass edge detector).
	www.dai.ed.ac.uk /HIPR2/sobel.htm (1115 words)

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