In this paper, the method of stomach extraction is proposed. First, the approximate region of stomach is obtained by the combination image which is constructed from binarize of original image and its differential image. The reference direction data are obtained by the approximate contour of stomach. and their data are made by the following algorithm. (1) The connected components on edge line of the approximate region are recorded in clockwise rotation. (2) Each direction datum is recorded at the left adjacent pixel. However, the direction datum has already been existed at the pixel, the pixel is excluded from the consideration. (3) The large areas are constructed by each pixel in the size of 2 x 2 pixels. (4) All pixels in large area are checked. If all pixels do not have the direction datum, nothing is processed. If only one pixel in the large area has the direction datum, the datum is stored into another pixels. If there are two or more direction data in the large area, the average of their data is recorded at the empty pixel. If all pixels have the direction datum, nothing is processed. (5) The size of large area is changed in each size of 4 x 4, 8 x 8, 16 x 16, 32 x 32, 64 x 64, and the processing (4) is carried out. Next, the stomach contour is extracted by tracking the brightness of differential image. When the tracking direction isselected, the direction with maximum value of brightness of differential image is decided in the tracking direction. In thismethod, the reliable stomach contour is extracted by tracking the sharp edge. Then, in the part where the edge is unclear, thestomach contour is extracted in consideration for the reference data of direction. Therefore, the accurate stomach contour isextracted. Lastly, this method was applied for many samples of X-ray image, and was proved to be effective.

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