英语翻译
Step 4
Once the edge direction is known,the next step is to relate the edge direction to a direction that can be traced in an image.So if the pixels of a 5x5 image are aligned as follows:
Then,it can be seen by looking at pixel "a",there are only four possible directions when describing the surrounding pixels - 0 degrees (in the horizontal direction),45 degrees (along the positive diagonal),90 degrees (in the vertical direction),or 135 degrees (along the negative diagonal).So now the edge orientation has to be resolved into one of these four directions depending on which direction it is closest to (e.g.if the orientation angle is found to be 3 degrees,make it zero degrees).Think of this as taking a semicircle and dividing it into 5 regions.
Therefore,any edge direction falling within the yellow range (0 to 22.5 & 157.5 to 180 degrees) is set to 0 degrees.Any edge direction falling in the green range (22.5 to 67.5 degrees) is set to 45 degrees.Any edge direction falling in the blue range (67.5 to 112.5 degrees) is set to 90 degrees.And finally,any edge direction falling within the red range (112.5 to 157.5 degrees) is set to 135 degrees.
Step 5
After the edge directions are known,nonmaximum suppression now has to be applied.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.This will give a thin line in the output image.
不要用机译，可以软件辅助，但要整理好并使用专业词汇，翻译好的话可以加分