![]() ![]() The pixels with the largest gradient values in the direction of the gradient become edge pixels, and edges may be traced in the direction perpendicular to the gradient direction. ![]() After gradient images have been computed, pixels with large gradient values become possible edge pixels. One of the most common uses is in edge detection. To get the full range of direction, gradient images in the x and y directions are computed. Each pixel of a gradient image measures the change in intensity of that same point in the original image, in a given direction. Gradient images are created from the original image (generally by convolving with a filter, one of the simplest being the Sobel filter) for this purpose. Image gradients can be used to extract information from images. Gray pixels have a small gradient black or white pixels have a large gradient. On the right, a gradient image in the y direction measuring vertical change in intensity. In the center, a gradient image in the x direction measuring horizontal change in intensity. On the left, an intensity image of a cat. ![]() GIS tools use color progressions to indicate elevation and population density, among others. Image gradients are often utilized in maps and other visual representations of data in order to convey additional information. The most common way to approximate the image gradient is to convolve an image with a kernel, such as the Sobel operator or Prewitt operator. Approximations of these derivative functions can be defined at varying degrees of accuracy. With some additional assumptions, the derivative of the continuous intensity function can be computed as a function on the sampled intensity function, i.e., the digital image. Since the intensity function of a digital image is only known at discrete points, derivatives of this function cannot be defined unless we assume that there is an underlying continuous intensity function which has been sampled at the image points. At each image point, the gradient vector points in the direction of largest possible intensity increase, and the length of the gradient vector corresponds to the rate of change in that direction. Mathematically, the gradient of a two-variable function (here the image intensity function) at each image point is a 2D vector with the components given by the derivatives in the horizontal and vertical directions. Another name for this is color progression. In graphics software for digital image editing, the term gradient or color gradient is also used for a gradual blend of color which can be considered as an even gradation from low to high values, as used from white to black in the images to the right. For example, the Canny edge detector uses image gradient for edge detection. The gradient of the image is one of the fundamental building blocks in image processing. An image gradient is a directional change in the intensity or color in an image. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |