Roger L. Triplett

Noise measurement technique for document scanners

Scanner noise is one of the fundamental parameters of image quality. In this paper, we present an algorithm developed to derive the noise of a scanner using the 2D Wiener spectra of the test pattern and the scanners MTF. The Wiener spectra of the test pattern was measured and its contribution to the measured RMS noise was estimated by integrating the volume under the product of the test pattern Wiener spectra and the scanners MTF. The test pattern contribution was then removed from the measured noise. The derived noise agrees very well with the noise model for both drum scanner and CCD scanners. The structured 1D noise is also of interest especially when evaluating CCD scanner systems. A method was described to accurately determine 1D structured noise by averaging over fast scan and slow scan directions. Finally an experiment was conducted to verify the noise measurement technique. The true noise of a drum scanner was measured at its analog output terminal, and was compared to the noise estimated with the proposed new noise metric. The agreement between hardware measured noise and the estimated noise is very good with RMS error of less than 0.001 in reflectance unit. With this new technique, we can effectively improve the noise measurement accuracy by a factor of up to 500% for a photographic test pattern.