roi construction u201d of the invention the modification of full matching is carried out for the sample points sequentially in order to calculate the disparity value due to the disparity value of left image and right image is close for y coordinate of every pixel in the same frame the highest one in top 20 will be used as the reference of the following sample point thus the searching height can be reduced and the computation efficiency can be increased effectively without influencing the accuracy rate as for the object tracking 144 shown in fig4 the frames own the continuity which means the object will be appeared again in the next frame when current frame possesses the object the object tracking process is carried out to raise the computation efficiency and the accuracy rate in addition when the vehicle coordinate information of previous frame is used the range can be increased to carry out the horizontal and vertical edge projection to obtain the highest and the second highest position in order to cut the coordinate information quickly and correctly the disparity value of previous frame can be used as the reference for the starting point of searching in the frame it means the following computation is carried out in the modification of full matching the original variable j is from 0 to sw u2212 1 it will be renewed as a new range.