Image quality cannot be quantified completely by a single metric.  We can, however, quantify different aspects of image quality.   For example, we know that the visibility of spatial, temporal or color distortions affect subjective judgments of image quality.  

ISET includes software for calculating a variety of metrics that predict the visibility of color, spatial and temporal distortions.  The metrics, CIELAB DE and Spatial-CIELAB,  are designed to operate on a standard set of input images. 

In addition to these tools, ISET includes standard test images to evaluate color  (e.g., Gretag ColorChecker) and pattern (Mackay Chart) and spatial targets designed by ImagEval Consulting.