Watson & Ramirez (2000) proposed a standard observer for spatial vision that is intended to extend existing photometric and colorimetric standard observers into the realm of spatial patterns. Given a pair of images, it computes the perceptual distance between them in units of JND. It is designed for applications in which simplicity and standardization, as well as accuracy, are important. Here we report the following updates (1, 2) and enhancements (3, 4) to the original proposal. 1) The models for the oblique effect and the contrast sensitivity function have been amended. 2) New model parameters have been estimated based on the new model and the expanded ModelFest data set (Carney, et al., 2000). 3) A local masking model has been added that is essential when the two images share a common pattern background. 4) Optional extensions of the metric are provided for the color (Wuerger, Watson, & Ahumada, 2002) and time domains.

Watson, A. B., & Ramirez, C. V. (2000). A Standard Observer for spatial vision [Abstract]. Investigative Ophthalmology and Visual science, 41(4), S713.

Carney, T., Tyler, C. W., Watson, A. B., Makous, W., Beutter, B., Chen, C.-C., et al. (2000). Modelfest: year one results and plans for future years. SPIE Proceedings, 3959, 140-151.

Wuerger, S., Watson, A.B., and Ahumada, A.J., Jr. (2002) Toward a standard observer for spatio-chromatic detection. SPIE Proceedings 4662, 159-172.

Supported by NASA 131-20-20 and NASA 711-51-12.