PURPOSE: To improve the efficiency of a print and photoengraving process by controlling the size of an output picture and aspect ratio with the processing of picture data to be inputted, without changing the operating condition of an output plotter, in a picture data output plotter.

CONSTITUTION: A converter 1 processes a picture data DI for each scanning line in response to the preset power deletes a picture data for scanning line's share in reaching the prescribed scanning line or increases ≥1 scanning line. Every time the picture data for one scanning line's share is inputted to attain the discrimination, the power is added sequentially, the part less than the decimal point of the integrated value is added again with the power and the integer part K is checked. When the integer part K is ≥2, (K-1)-line picture data are added in succession to the picture data for one scanning line's share, and when the integer part K does not reach 1, the picture data inputted for the case is delected and the output is attained from the picture data inputted next. Thus, the size and the aspect ratio of the reproduced picture are controlled by having only to process the input picture data.