1. A method for enlarging or reducing an image on a display screen of a computer system, said method comprising: detecting, by a processor of the computer system, a pointing operation that points to, with a single touch gesture of a pointing means on the display screen, a first-drawn figure indicative of a range of the image to be enlarged or reduced and a second-drawn figure indicative of a size of the enlarged or reduced range; detecting, on the display screen by the processor, a first trajectory traced by a first movement of a position pointed to on the display screen with a single-touch gesture of a pointing means; detecting, by the processor, a second trajectory traced by a second movement of a position pointed to on the display screen with a single-touch gesture of the pointing means; determining, by the processor, that the second movement tracing the second trajectory occurred after the first trajectory was traced; determining, by the processor, that the first trajectory is a first noisy circle having a radius R 1 ; determining, by the processor, that the second trajectory is a second noisy circle having a radius R 2 , wherein either R 1 <R 2 or R 1 >R 2 ; recognizing the first-drawn figure and the second-drawn figure; and displaying, on the display screen in response to the detection of the pointing operation, an enlarged or reduced image obtained by enlarging or reducing the image at an enlargement or reduction ratio determined based on the first-drawn figure and the second-drawn figure, wherein in response to having determined that R 1 <R 2 or having determined that R 1 >R 2 , the image is enlarge or reduced, respectively, either by a scale factor of about a ratio of R 2 /R 1 or by a selection of an image of multiple stored images having different respective enlargement ratios or reduction ratios with respect to the first noisy circle.