The object is for drawing a contour line of an overlapped part from which a feeling of strangeness is not acquired in a case where a plurality of tuned objects are overlapped with one another in an image generated by a perspective transformation process. A tuned object A (a line width of the contour line is "3") is overlapped with a tuned object B (a line width of the contour line of "1") located in a position closer to a virtual screen than the tuned object A. Each pixel included in the tuned object A is set as a target pixel, and a pixel located in a position shifted from the target pixel by the line width is set as a determination pixel. When depth data and line width data of the determination pixel is smaller than those of the target pixel, the line width data of the target pixel is reset to the line width data of the determination pixel, and a pixel located in a position shifted from the target pixel by the reset line width is reset as the determination pixel. When the depth data of the target object is not smaller than that of the determination pixel, contour line data is written into the target pixel.
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