A simple method to measure the resolution of digital image input devices is reported. The method, called the curve-fitting method (CFM), is based on a Gaussian impulse response model for the devices and a curve-fitting technique. The advantage of the CFM over the contrast transfer function (CTF) method is its great convenience, especially when a local measurement is intended. The average time of the measurement, which is made by running a curve-fitting program, is about 15 s.