A cross media tonal mapping model obtained from psychometric experiments

摘要

We study cross-media image reproduction by constructing a tonal range mapping model. We aim at making reproductions that optimally represent the overall appearance of the originals despite a reduction in dynamic range. We propose a general mapping that works for all input and output white and black points. It is described by a two parameter functional model. The parameters are chosen so that one primarily corresponds to black point variations and the other to white point variations. We set up psychometric experiments to estimate optimal parameter values. Paired comparison was employed because of its ease of use and accurate results. To keep the number of observations down, a small pilot experiment marks out a narrower range of values first. Furthermore, the two parameter optimisation is split into a sequential single parameter optimisation. The experiments are repeated for different white and black points. The model is completed by interpolating between the experimental points and determining the correlation between the parameters. A separate verification experiment proves the validity of the model within the experimental accuracy. A comparison of our model with the CIECAM97s colour appearance model clarifies the fundamental difference between them. The tonal mapping model aims at the best overall reproduction of images. It produces more pleasing images by giving them higher overall contrast, whereas CIECAM faithfully models the appearance.