Color-dependent Banding Characterization and Simulation on Natural Document Images

摘要

Print defects like banding from a digital press involve not only luminance variation, but also chrominance variation. As digital presses place one color separation at a time, the contrast and spatial pattern of the print defects are color-space dependent. Characterizing the color-dependent features of the banding signal enables us to simulate the banding on natural document images in a more accurate way that matches the characteristics of the banding generation mechanism within the digital press. A framework is described for color-dependent banding characterization including the following steps: printing and scanning uniform patches that sample colorant combinations throughout the input document sRGB color space, extracting banding signals in the CMYK color space of the target device, and modeling the banding features in a perceptually uniform color space. We obtain a full banding features LUT for every color point in the input sRGB space by interpolating banding features extracted from measured color points. The color-dependent banding simulation framework is developed based on the banding features LUT. Using the information contained in this LUT, a single banding prototype signal is modulated in a color-space-dependent fashion that varies spatially across the natural document image. Proper execution of the framework of banding characterization and simulation requires careful calibration of each system component, as well as implementation of a complete color management pipeline.