# What is meant by edge detection in image processing,ford ka engine swap,best books for 2nd graders,ed edd n eddy may i have this dance - Easy Way

Science, Technology and Medicine open access publisher.Publish, read and share novel research. Template Matching Approaches Applied to Vertebra DetectionMohammed Benjelloun1, Said Mahmoudi1 and Mohamed Amine Larhmam1[1] Department of Computer Science, Faculty of Engineering University of Mons, Belgium1.

Figure 3 and figure 4 show the results obtained by using the region selection method combined to the Harris corner detector [8] applied to X-ray image of the cervical spinal column. Geometric model construction: In this step, we build a vertebra mean model representing the average shape corresponding to a set of 25 vertebrae. Gradient computation and edge detection: We use the canny operator to extract the edge of the vertebrae mean model.

Contrast-Limited Adaptive Histogram Equalization:This step aims to prepare the X-ray images to edge detection by using the Contrast-Limited Adaptive Histogram Equalization (CLAHE) [3] technique used to improve the image contrast. Gradient computation and edge detection:In this step, we repeat the same process described in the model construction. Semi-automatic: Two points are placed to make a sub-image covering the area of cervical vertebrae. Accumulator construction:This step represents the core of the Generalized Hough Transform detection.

Except where otherwise noted, this work is licensed under Creative Commons Attribution-NonCommercial 4.0 International License. Background: Common carotid artery (CCA) ultrasound with measurement of intima-media thickness (IMT) is a safe and noninvasive technique for assessing subclinical atherosclerosis and determining cardiovascular risks. Objectives: The aim of this study was to compare different edge detection techniques with speckle reducing anisotropic diffusion (SRAD) de-noising filter in ultrasound images of both arteries. Patients and Methods: In a cross-sectional design, an examination was performed on ten men with mean age of 40 A± 5 years from September 2012 to March 2013 through random sampling.

Results: The lowest values of MSE and highest values of PSNR were achieved by Canny edge detection with de-noising SRAD filter for IMT of left CCA and BA in 90 frames.

Conclusions: Based on the result, by measuring the MSE and PSNR, this study showed Canny edge detection with SRAD filter is better than other edge detections in terms of speckle suppression and details preservation in CCA and BA ultrasound images.

Ultrasound imaging is broadly used to show carotid, femoral, brachial and other peripheral arteries. The aim of this study was to compare different edge detection techniques with SRAD de-noising filter in ultrasound images of common carotid and brachial arteries for optimum removal of noise with preservation of edges.

The edge detection process involves small kernels that convolve with an image to estimate the first-order directional derivatives of the image brightness distribution.

The Sobel operator (11, 12) is a discrete operator, which computes the gradient for intensity changes at each point in an image. The Roberts operator (13) performs a simple, quick to compute, two-dimensional (2-D) spatial gradient measurement on an image. The 2 A— 2 kernels for Roberts operator (Rx and Ry are gradient components for the horizontal and vertical edge orientations). Prewitt operator (11, 13) is a discrete differentiation operator which functions similar to the Sobel operator, by computing the gradient for the image intensity function. The 3 A— 3 kernels for Prewitt operator (Px and Py are gradient components for the horizontal and vertical edge orientations). As shown here, the input image is illustrated as a set of discrete pixels; a discrete convolution kernel can approximate the second derivative in the definition of the Laplacian.

Canny edge detector first smoothes the image to remove noise and then determines the image gradient to highlight regions with high spatial derivatives. The speckle reduction anisotropic diffusion (SRAD) method (15, 16) is used directly for suppressing speckle noise in ultrasound and radar images.

I am trying to implement Epshtein's paper(Detecting text in natural scenes with stroke width transform(2010)) on text detection in natural images. As per belisarius's suggestion, I found that mean-shift filter works quite well for text region segmentation. Stroke Width works well with chars like 'H''Y' even for 'S' because the corresponding edges are usually at constant distance if we proceed in the direction of gradient. Take a look at the Matlab documentation for edge and the Wikipedia article on the Canny algorithm. Not the answer you're looking for?Browse other questions tagged image-processing ocr image-segmentation or ask your own question.

For example, the following shows the picture of a building along with its histogram (original image from Microsoft Research Digital Image. The following shows the edge detection results using Canny algorithm (left image uses mean value auto-thresholding, right image uses median value auto-thresholding) and the results exhibit very little visible differences. And after image equalization, both mean and median value auto-thresholding achieved similar results. So the Canny edge detection using median value auto-thresholding seems to adapt to different types of images very well (note selecting the median value selection can be thought as equalizing the histogram, except that the pixel values are not changed during such operation). If you had 20 bins, a min of 20 a max of 220 you would have a step of 10 which would give you a max bin value of (20+10*(19))=210 so your histogram would never have any values for the bin between 210 and 220.

The different steps of the detection process using the region selection method combined to the Harris corner detector. The modelling process results (a) Vertebra mean model, (b) Edge detection result, (c) the template shape constructed from the R-Table. The proposed edge detection approach in case of cervical vertebrae (a)the original X-ray image, (b) the improved image, (c) The Canny edge detection result.

Final result detection of C3 to C7 cervical vertebrae with the automaticapproach (a) Five detection and one false positive, (b)Three detections and four false positives.

Final result detection of C3 to C7 cervical vertebrae with the semi-automatic approach for two cases.Table 2.

This template function represents an inter-vertebral model, which is calculated according to the shapes of the areas between vertebrae. We notice that the process of region selection, Figure 3, gives very good results and permit to isolate each vertebra separately in a polygonal area. We have in general many occurrences of the same orientation as we move around the boundary. The approximation is performed in horizontal and vertical directions by applying the two masks shown in equation (4). Potential vertebrae centers detectionFor the vertebrae detection we propose two alternative approaches, Automatic and semi-automatic detection.

It computes first different local histograms corresponding to each part of the image, and uses them to change the contrast of distinct regions of the image. Therefore, edge detection with Canny filter is applied to the improved image, and sobel operator is performed in –x and –y directions. It aims to determine the position of the center points of vertebrae in the input X-ray image by using the information stored in the R-table. Moreover, the pattern of wall thickening in the brachial artery (BA) is rather diffuse compared to the carotid artery and may be a more sensitive indicator of long-term systemic exposure to risk factors. There are several important benefits of using ultrasound in comparison to other techniques. Kernels are pre-defined groups of edge models that match each image segment of a fixed size. The 3*3 kernels for the Sobel operator (Sx and Sy are gradient components for the horizontal and vertical edge orientations). The angle of orientation of the edge (relative to the pixel matrix) giving rise to the spatial gradient is extracted by: (4).

These kernels are designed to respond maximally to edges running at 45 to the pixel matrix; one kernel for each of the two perpendicular orientations. The Prewitt edge detection operator is used for detecting vertical and horizontal edges of images (equation 6) (6).

The Laplacian of an image highlights districts of rapid intensity change and is therefore often used for edge detection. Since these kernels are approximating a second derivative measurement on the image, they are extremely sensitive to noise. The algorithm then tracks along these districts and suppresses any pixel that is not at the maximum (non-maximum suppression). The SRAD method uses an instant coefficient that is a function of local gradient, magnitude and Laplacian operators.

Now I am facing another problem in the implementation of Stroke Width transform(look at Epshtein's paper). For one portion of left edge of 1st upstroke we get the right edge of 2nd upstoke as its correspoding edge.

One issue with Canny edge detection algorithm is that we need to specify a high threshold and a low threshold. It is widely used in image processing and provides an accurate result for edge detection.Within this operator, the image is first smoothed to reduce the noise. Finally, an edge tracking by hysteresis is used, where high and low threshold are defined to make a filter for pixels of the last image.The canny edge detection result is shown in Figure 2(b). We make a preliminary pre-processing step based on histogram equalization to enhance X-ray images.

The result of the edge detection is showen in figure 13(c).Region of interest selection We made two alternative approaches of our selection of Region of Interest (ROI).

In practice, each point from the edge detection results, figure 13(c), votes for different possible centers.

Therefore noninvasive evaluation of mechanical parameters changes of both arteries has gained the attention of researchers.

The program was designed in the MATLAB software to extract consecutive images in JPEG format from the AVI. Most importantly, B-mode ultrasound imaging is non-invasive and allows real time conception of arterial morphology, which is not currently possible with any other imaging tool (1). These kernels are designed to respond maximally to edges running vertically and horizontally relative to the pixel matrix; one kernel for each of the two perpendicular orientations.

The kernels can be used several times in the input image, to create independent measurements of the gradient component in each orientation (Rx and Re).

The Laplacian is often used for an image that has first been smoothed with something approximating a Gaussian-smoothing filter in order to reduce its sensitivity to noise. To indicate this, the image is often Gaussian smoothed before applying the Laplacian filter. The SRAD method is based on a partial differential equation (PDE) that includes the imaging gradient, Laplacian and image intensity. Now i want to count the number of pixels in sclera so that when i close my eyes i get reduced number of pixels and conclude that my eye is closed and apply blink function. Medical Imaging provides very useful information about the patient's condition, and the adopted treatment depends on the symptoms described and the interpretation of this information. Polar signatureA second segmentation approach that we proposed to apply after the region selection process is based on a polar signature [8] representation associated to the polygonal region for each vertebra described on section 2.1.

The selection is based on the gradient direction of the target point and its corresponding information in the R-table.

Another program was designed in the MATLAB software to apply regions of interest (ROI) on the IMT of the posterior wall of common carotid and brachial arteries.

Furthermore, the non-invasive nature provided by B-mode ultrasound imaging and its low cost has allowed the use of this technique for more clinical studies, which show a major relationship between carotid intima-media thickness (IMT) and cardiovascular disease (CVD) (2). If the value is not smaller than a given threshold, then the pixel is categorized as an edge.

The operator commonly takes a single gray level image as input and produces another gray level image as output. This introduces significant variance in the stroke width of the region of 'W' leading to terming this as non-text region according to paper. We choose to use this approach in order to explore all region points likely to be corresponding to vertebra contours.For each vertebra we use as center of the polar coordinate system the click point initially used for the region selection step.

Ultrasonic B-mode images from IMT of common carotid artery (CCA) are used broadly as a measure of atherosclerosis and in studies on atherosclerosis as the determinant of CVD.

All the gradient-based algorithms have kernel operators that estimate the edge strength in directions, which are orthogonal to one another, generally vertically and horizontally. Hysteresis applies two thresholds and if the magnitude is lowers than the first threshold, it is adjusted to zero (made a non-edge). In this blog post, I will examine a couple of simple methods that can be used to automatically determine the threshold values. In this difficult task, medical images processing presents an effective aid able to help medical staff.

For the beginning direction, we chose the average direction between the frontal line direction and the posterior line. For this reason, we add a new parameter to make a range of scale to enhance the detection process.

Finally, the program measured mean-squared error (MSE) and peak signal to noise ratio (PSNR). Carotid IMT has been shown to be related to cardiovascular risk factors, current CVD, and atherosclerosis in the peripheral coronary, femoral and brachial arteries (3).

This is nowhere clearer than in diagnostics and therapy in the medical world.We are particularly interested to detect and extract vertebra locations from X-ray images.

We rotate the radial vector 360° around the central points with a step parameter expressed in degrees. Ultrasound images edge detection is important for recognition of IMT in CCA and brachial artery (BA). Edge detection algorithms are grouped into two categories, namely, gradient operator and Laplacian operator.

Furthermore, if the magnitude is between the two thresholds, then it is set to zero unless there is a path from this pixel to a pixel with a gradient above the second threshold. Generally, edge is detected according to algorithms such as Sobel, Roberts, Prewitt, Canny, and LOG (Laplacian of Gaussian) operators (4), yet in theory they consist of high pass filtering, which are not appropriate for noise ultrasound image edge detection because noise and edge belong to the range of high frequency (5, 6).

The gradient operator detects edge pixels by obtaining the maximum and minimum value at the first derivative level on the image.

Actually, these contributions are mainly interested in only 2 medical imagery modalities: Computed Tomography (CT) and Magnetic Resonance (MR). Indeed, for a better approximation of vertebra contours, we use a second degree polynomial fitting [9, 10]. Naturally, an ultrasound image includes more noise content, especially speckle noise, than any other imaging modality (6). The classical gradient operators selected in this work are Sobel, Prewitt, Muthukrishnan and Radha (11). Speckle is the artifact caused by interference of energy from randomly distributed scattering objects which reduces image resolution and contrast and blurs essential details.

Laplacian operator is a second order derivative, where the value of edge pixel at the first derivative is referred to as zero-crossing at the second derivative (11).

Vertebral Faces DetectionIn this method, we proceed by detecting the four faces belonging to vertebrae contours.

Therefore, speckle noise suppression is an important requirement whenever ultrasound imaging is used (6, 7). In addition, from the point of view of the patient, this procedure has the advantage to be more safe and non-invasive. We propose an individual characterization of each vertebra by a set of four faces, (anterior, posterior, inferior and superior faces).

Traditional speckle removal filters, like the Lee filter and Frost filter have greater restrictions in edge and characteristics preservation (9). Despite these valuable benefits, the interpretation of images of this type remains a difficult task now. The resulting regions obtained are used to create a global polygonal area for each vertebra. A noise reduction filter such as conventional anisotropic diffusion is not appropriate for speckle suppression (8). Another stage considered as a second pre-treatment step is the computation of the image gradient magnitude on vertebrae regions. The conventional anisotropic is not appropriate for multiplicative noise-including speckle and it is instead effective for additive noise. Indeed, in practice, these images are characterized by a low contrast and it is not uncommon that some parts of the image are partially hidden by other organs of the human body. This process allows a first approximation of the areas belonging to vertebrae contours, figure 7.

As a result, the vertebra edge is not always obvious to see or detect.In the context of cervical spinal column analysis, the vertebra edges detection task is very useful for further processing, like angular measures (between two consecutive vertebrae or in the same vertebra in several images), vertebral mobility analysis and motion estimation.

To extract faces vertebrae contours, we propose a template matching process based on a mathematical representation of vertebrae by a template function. However, automatically detecting vertebral bodies in X-Ray images is a very complex task, especially because of the noise and the low contrast resulting in that kind of medical imagery modality. The SRAD filter joins both the additive noise reduction anisotropic diffusion filtering process and the adaptive speckle (multiplicative noise) filtering process (9). The goal of this work is to provide some computer vision tools that enable to measure vertebra movement and to determine the mobility of each vertebra compared to others in the same image.The main idea of the proposed work in this chapter is to locate vertebra positions in radiographs. It makes the generation of image scale area possible (a set of filtered images that alter from fine to coarse) without bias and with filter window size and shape (9). This operation is an essential preliminary pre-processing step used to achieve full automatic vertebra segmentation. The SRAD filter not only protects edges but also enhances edges by eliminating diffusion across edges and allowing diffusion on either side of the edge (8).

The goal of the segmentation process is to exploit only the useful information for image interpretation.

The reader is lead to discover [1] for an overview of the current segmentation methods applied to medical imagery.

Active shape model based segmentation:In this section, we describe another method that we proposed for cervical vertebra segmentation in digitized X-ray images. This segmentation approach is based on Active Shape Model method [12, 13,14] whose main advantage is that it uses a statistical model. The level set method is a numerical technique used for the evolution of curves and surfaces in a discrete domain [2].

This model is created by training it with sample images on which the boundaries of the object of interest are annotated by an expert. The advantage is that the edge has not to be parameterized and the topology changes are automatically taken into account.

The active contour algorithm deforms and moves a contour submitted to internal and external energies [4]. A special case, the Discrete Dynamic Contour Model [5] has been applied to the vertebra segmentation in [6].

We proposed an approach which consists on modelling all the shapes of vertebrae by only one vertebra model.

Other methods exist and without being exhaustive, let’s just mention the parametric methods [15], or the use boundary based segmentation [16] and also Watershed based segmentation approaches [17].The difficulties resulting from the use of X-ray images force the segmentation methods to be as robust as possible. Indeed, the multiple tests which we carried out on a large dataset composed of varied images prove the effectiveness of the suggested approach. In this chapter, we propose, in the first part, some methods that we have already used for extracting vertebrae and the results obtained.

The second part will focus on a new method, using the Hough transform to detect vertebrae locations.

Indeed, the proposed method is based on the application of the Generalized Hough Transform in order to detect vertebra positions and orientations. Shape detection using Generalized Hough TransformIn this section, we propose a cervical vertebrae detection method using a modified template matching approach based on the Generalized Hough Transform [18]. For this task, we propose first, to use a detection method based on the Generalized Hough Transform and in addition, we propose a cost function in order to eliminate the false positives shapes detected. The Hough Transform is an interesting technique used in image analysis to extract imperfect instances of a shape in images by a voting procedure. This chapter is organized as follow: In section 02 we present some of our previous works composed of two category of method.

The detection process that we propose starts with the determination of the edges on the radiography.

The firsts are based on a preliminary region selection process followed by a second segmentation step. We have proposed three segmentation approach based on corner detection, polar signature and vertebral faces detection. After this step, the detection algorithm selects among the edges which one look the most similar to the vertebra shape by using the Generalized Hough Transform (GHT) accumulator.For our experiments, we used 40 X-Ray radiographs coming from the NHANES II database. The second category of methods proposed in this chapter is based on the active shape model theory. These images were chosen randomly but they all are focused on the cervical vertebrae C3 to C7. In section 03 we describe a new automatic vertebrae detection approach based on the Generalized Hough transform.

Previous workIn this part, we provide an overview of the segmentation approach methods that we have already applied to vertebrae detection and segmentation. After applying the detection process using the GHT method and the cost function proposed, all the vertebrae were detected perfectly. The first one were based a regions selection process allowing the detection of vertebra orientations and inter-vertebral angles and the second based of the active shape model theory.

R-Table construction The Generalized Hough transform (GHT) is a powerful pattern recognition technique widely used in computer vision. Region selectionIn this section, we propose a first pre-processing step which allows the creation of a polygonal region for each vertebra. It was initially developed to detect analytic curves (lines, circles, parabolas, etc.) from binary image and extended by D.

This pre-treatment is achieved by a template matching approach based on a mathematical representation of the inter-vertebral area. Indeed, each region represents a specific geometrical model based on the geometry and the orientation of the vertebra. We suggest a supervised process where the user has to click once at the center of each vertebra to be analyzed.

The detection process of the GHT is presented as two main parts:The R-Table is a discrete lookup table made to represent the model shape.

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