In a graphic processor, a rendering control circuit carries out weighted averaging on pieces of pixel data of source image information arranged to form a pixel-data matrix corresponding to a pixel matrix with columns of the pixel-data matrix being oriented perpendicularly to a scanning direction in order to compute a weighted average of pieces of pixel data on rows of the pixel-data matrix adjacent to each other and on a column of the pixel-data matrix perpendicular to the scanning direction in so-called blend processing. It is thus possible to eliminate a difference in image information between adjacent scanning lines, which is big in some cases. In this case, the rendering control circuit reads out pieces of pixel data from the pixel-data matrix sequentially in a direction perpendicular to the scanning direction and computes a weighted average of the pieces of data. It is therefore unnecessary to newly install a storage means, such as a line buffer, in a display control circuit and, particularly, in the rendering control circuit. Thus, even when image data subjected to blend processing is displayed by adopting an interlace scanning technique, undesired flickering is not generated.