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Understanding And Applying Machine Vision Part 6

Tham khảo tài liệu 'understanding and applying machine vision part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | NUMBER OF BITS 1 2 3 4 5 6 7 8 NUMBER OF GRAY LEVELS 2 4 8 16 32 64 128 257 The actual gray value is a function of the integration of four variables illumination viewpoint surface reflectance and surface orientation. The surface reflectance of an object is determined by such surface characteristics as texture and color material. The resulting distribution of light intensities forms an image. 7.3.2 Digitization What follows is a description of the digitization process taken from a paper entitled Understanding How Images Are Digitized given by Stanley Lapidus at the Vision 85 Conference. Page 154 The sampling process is illustrated in Figure 7.13. The top graph represents the cross section of a cut through a threedimensional illumination surface which could be taken as a representation of an optical image. In such a threedimensional illumination surfaces x and y are the coordinate axes of the plane in which an object is viewed and z is the intensity of the light falling on the object. Here z 0 represents black or total darkness and z very large represents a strong light intensity. Since the top graph represents a cross section of such an x y z surface the graph s vertical axis is z the light intensity and the horizontal axis is the x-wise extent of the three-dimensional illumination surface. The middle graph represents the sampling points in the x direction of the image plane. The bottom graph represents sampled discrete gray level values that correspond to the light intensity values of the top graph. Figure 7.13 Sampling process. Looking at the top graph some areas are white some are black and some are of gradually decreasing gray shades remember this is an illustration of an intensity profile the result of a part interacting with a lighting environment . Looking at the figure The first zone is exactly along a pixel boundary. The second zone is halfway between two pixels. The third zone is offset. Page 155 The fourth zone is gradually sloping. The fifth zone shows .