Tham khảo tài liệu 'dynamic vision for perception and control of motion - ernst d. dickmanns part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Efficient Extraction of Oriented Edge Features 135 ference is largest in amplitude the gradient over two consecutive mask elements is maximal. However due to local perturbations this need not correspond to an actual extreme gradient on the scale of interest. Experience with images from natural environments has shown that two additional parameters may considerably improve the results obtained 1. By allowing a yet to be specified number n0 of entries in the mask center Figure . Efficient mask evaluation with the Colsum -vector the Md-values given are typical for sizes of receptive fields formed to be dropped the results achieved may be more robust. This can be immediately appreciated when taking into account that either the actual edge direction may deviate from the mask orientation used or the edge is not straight but curved by setting central elements of the mask to zero the extreme intensity gradient becomes more pronounced. The rest of Figure shows typical mask parameters with n0 1 for masks three and five pixels in depth md 3 or 5 and with n0 2 for md 8 as well as n0 3 for md 17 rows b c . 2. Local perturbations are suppressed by assigning to the mask a significant depth nd which designates the number of pixels along the search path in each row or column in each positive and negative field. The total mask depth md then is md 2 nd n0. Figure shows the corresponding mask schemes. In line b a rather large mask for finding the transition between relatively large homogeneous areas with ragged boundaries is given md 17 pixels wide and each field with seven elements so that the correlation value is formed from large averages for a mask width nw of 17 pixels the correlation value is formed from 7-17 119 pixels . With the number of zero-values in between chosen as n0 3 the total receptive field mask size is 17-17 289 pixels. The sum formed from nd mask elements vector values ColSum divided by nw- nd represents the average intensity value in the oblique
