Abstract
In a digital camera printing system, dynamic range is usually compressed linearly in log-log scale and good image is obtained as a whole. However, the image has a tendency to give us a flat impression without liveliness compared with silver halide photography. So, a sigmoid function is proposed and is applied to tone rescaling. The sigmoid function has the characteristics that the γ value and the position of the steepest point of the curve of the function are adjustable. Several methods of determining the parameters of the sigmoid function are studied. When the steepest point is determined to the peak of the histogram of region of interest and γ value is adjusted to around 1.4, it is confirmed that the image quality is especially improved in subjective estimation.
