Identification of Image Noise Sources in Digital Scanner Evaluation

For digital image acquisition systems, analysis of image noise often focuses on random sources, such as those associated with quantum signal detection and signal-independent fluctuations. Other important noise sources result in pixel-to-pixel sensitivity variations that introduce repeatable patterns into the image data. In addition, because most analyses use a nominally uniform target area to estimate image noise statistics, target noise can often masquerade as noise introduced by the device under test. We describe a method for distilling various fixed-pattern and temporal noise sources. The method uses several replicate digital images acquired in register. In some cases, however, evaluation of several digital scanners reveals scan-to-scan variation in the image registration to the input test target. To overcome this limitation, a modified noise estimation method is described. This includes a step to correct this scan-to-scan misregistration. We also show that, in some cases, measurement of temporal and fixed-pattern noise sources can be achieved via the noise color covariance from a single test image.