Contrast sensitivity functions (CSFs) describe the smallest visible contrast across a range of stimulus and viewing parameters. CSFs are useful for imaging and video applications, as contrast thresholds describe the maximum of color reproduction error that is invisible to the human observer. However, existing CSFs are limited. First, they are typically only defined for achromatic contrast. Second, even when they are defined for chromatic contrast, the thresholds are described along the cardinal dimensions of linear opponent color spaces, and therefore are difficult to relate to the dimensions of more commonly used color spaces, such as sRGB or CIE L*a*b*. Here, we adapt a recently proposed CSF to what we call color threshold functions (CTFs), which describe thresholds for color differences in more commonly used color spaces. We include color spaces with standard dynamic range gamut (sRGB, YCbCr, CIE L*a*b*, CIE L*u*v*) and high dynamic range gamut (PQ-RGB, PQ-YCbCr and ICTCP). Using CTFs, we analyze these color spaces in terms of coding efficiency and contrast threshold uniformity.
Over the last 25 years, we have been involved in 3D image processing research field. We started our researches related to 3D image processing with “Data Compression of an Autostereoscopic 3-D Image” and presented our work in SPIE SD&A session in 1994. We first proposed the ray space representation of 3D images which is a common data format for various 3D capturing and displaying devices. Based on the ray space representation, we have conducted various researches on 3D image processing, which include: ray space coding and data compression, view interpolation, ray space acquisition, display, and a full system from capture to display of ray space. In this paper, we introduce some of our 25-year researches in terms of 3D image processing – from capture to display –.