JPS6411465A - Irradiation field recognition method - Google Patents

Abstract

PURPOSE:To recognize an irradiation field even when width is expanded to blur a contour, by deciding the position of an irradiation feild contour in a Y (X)-axial direction on an X (Y)-axis, and recognizing an area enclosed with the irradiation field contours in both axial directions as the irradiation field. CONSTITUTION:The differentiation value of respective position on each line is found by differentiating image data in the X-axial direction, and the positions A and B whose absolute values exceed a prescribed value are extracted for each line, and those two positions are set as contour candidate points which bear the irradiation field contour 2a in the Y-axial direction. By extracting the contour candidate points and projecting (adding and tabulating) them in the Y-axial direction, projected results are shown in which a range where no contour candidate point exists is shown linearly, and the range where the contour candidate point exists is extruded upward or downward. By detecting the extruded parts, extents w1 and w2 are found. Next, the position of the contour 2a corresponding to the extent on the X-axis is decided. Each of the extents w1 and w2 shows the range where the contour 2a corresponding to it exists, therefore, it is possible to decide accurately the position of the contour 2a on the X-axis by data based on the extent.