Hardcopy banding measurement and assessment
Abstract
Banding is a well-known printer artifact which generally appears as lines of variations in density running perpendicular to the process direction of the image. Banding is an important image quality issue; and it has been analyzed and assessed by many researchers. However, little literature has focused on the study of the relationship between physically measured banding and perceived banding. In the thesis we propose an experimental methodology for assessing banding which is based on the observers ability to discriminate between images with different levels of banding. We develop a method of measuring the amount of banding in hardcopy print. Using the method of constant stimuli, we conduct a psychophysical discrimination experiment for a given printer to obtain the difference threshold (DL). Our results show that the Weber fraction for discriminating banding remains constant over the printers despite differences in the spectral characteristics. This suggests that banding discrimination appears to be similar to many other perceptual phenomena (Weber's law holds). The obtained DL allows us to predict how much the banding power should be reduced in order to achieve a significant decrease in the perceived banding. ^ We also describe new cross-platform experiments using 10 different laser printers having different imaging characteristics. We analyze banding of the ten printers with line screen patterns. The experimental results identify the points of subjective equality of the ten printers relative to the banding of a reference printer, and provide the basis of a method of computing banding power by considering a contrast sensitivity function. Our results show that regardless of different banding spectral characteristics, the contrast banding power of a given printer can be mapped to the contrast banding power of one reference printer with added extrinsic banding. This implies that using our technique, we can reliably estimate the perceived amount of banding in a printer. ^
Degree
Ph.D.
Advisors
Jan P. Allebach, Purdue University.
Subject Area
Engineering, Electronics and Electrical
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