Method, apparatus and recording medium for interpolation operation

摘要

An interpolated image having high sharpness and no artifacts at a portion of changing transparency can be obtained for image data having the alpha channel. Upon interpolating original image data SO, whether or not the value of the alpha channel is 1 for all 4x4 pixels surrounding an interpolation point is judged by judging means. When the value is judged to be 1 for all pixels, the area is judged to be completely opaque and a high degree interpolation operation enabling sharpness increase is carried out by high degree interpolation operation means. If the value is judged to be not 1 for all pixels, a linear interpolation operation such as the pre-multiplied alpha method is carried out by linear interpolation operation means in order not to create an artifact. The interpolated image data obtained in this manner are composed together with combining image data by image composition controlling means to obtain composite image data.