An image processing method is a method for correcting both an image quality of an overall image and an image quality of a partial image with excellent balance. Thus, the seat tube of the bicycle is clamped between the two clamping blocks of the respective clamping unit, so that the bicycle is fixed by the respective clamping unit rigidly and stably without detachment. In a second signal path, the signal is amplified by a constant gain and by a variable gain amplifier.