1. A method for detecting a drivable region of a road, comprising the steps of: generating, using a camera, a gray-scale map including the road; deriving a disparity map from the gray-scale map including the road and detecting the road from the disparity map; removing, using a processor, a part with a height above the road greater than a predetermined height threshold from the disparity map so as to generate a sub-disparity map; converting, using the processor, the sub-disparity map into a U-disparity map; detecting, using the processor, the drivable region from the U-disparity map; and converting the drivable region detected from the U-disparity map into the drivable region within the gray-scale map, the detecting including performing a first detecting operation, the first detecting operation including detecting a specific region from the U-disparity map as the drivable region by shifting a detection window with a predetermined size from an initial position in the U-disparity map, the performing the first detecting operation including, (a) horizontally shifting the detection window along a direction of rows to the left from the initial position, and stopping the shifting of the detection window and recording the stop position of the detection window as a left stop position of the said row if a first determined condition is met, horizontally shifting the detection window along a direction of rows to the right from the initial position, and stopping the shifting of the detection window and recording the stop position of the detection window as a right stop position of the said row if a second determined condition is met; (b) shifting the detection window upward by a distance equal to the height of the detection window, and repeating step (a); (c) repeating step (b) until the detection window reaches a top edge of the U-disparity map or the left stop position and the right stop position in the same row are adjacent to each other; and (d) extracting a region covered by the shifted detection windows from the U-disparity map as the drivable region, wherein the first determined condition is one of the condition that the number of the active points within the detection window is greater than a predetermined number threshold; the condition that the detection window reaches a left edge of the U-disparity map, even though the number of the active points within the detection window is not greater than the predetermined number threshold; and the condition that the horizontal distance between the position of the detection window and the left stop position of the previous row is less than a first distance threshold, even though the detection window does not reach the left edge of the U-disparity map and the number of the active points within the detection window is not greater than the predetermined number threshold, wherein the second determined condition is one of the condition that the number of the active points within the detection window is greater than a predetermined number threshold; the condition that the detection window reaches a right edge of the U-disparity map, even though the number of the active points within the detection window is not greater than the predetermined number threshold; and the condition that the horizontal distance between the position of the detection window and the right stop position of the previous row is less than a second distance threshold, even though the detection window does not reach the right edge of the U-disparity map and the number of the active points within the detection window is not greater than the predetermined number threshold.