BTF-CIELab: A Perceptual Difference Measure for Quality Assessment and Compression of BTFs

Driven by the advances in lossy compression of bidirectional texture functions (BTFs), there is a growing need for reliable methods to numerically measure the visual quality of the various compressed representations. Based on the CIE Delta E-00 colour difference equation and concepts of its spatio-temporal extension ST-CIELab for video quality assessment, this paper presents a numerical quality measure for compressed BTF representations. By analysing the BTF in its full six-dimensional (6D) space, light and view transition effects are integrated into the measure. In addition to the compressed representation, the method only requires the source BTF images as input and thus aids the objective evaluation of different compression techniques by means of a simple numerical comparison. By separating the spatial and angular components of the difference measure and linearizing each of them, the measure can be incorporated into any linear or multi-linear compression technique. Using a per-colour-channel principal component analysis (PCA), compression rates of about 500:1 can be achieved at excellent visual quality.