Development of the I3A CPIQ spatial metrics

The I3A Camera Phone Image Quality (CPIQ) initiative aims to provide a consumer-oriented overall image quality metric for mobile phone cameras. In order to achieve thisgoal, a set of subjectively correlated image quality metrics has been developed. This paperdescribes the development of a speci“c group within this set of metrics, the spatial metrics.Contained in this group are the edge acutance, visual noise and texture acutance metrics.A common feature is that they are all dependent on the spatial content of the speci“cscene being analyzed. Therefore, the measurement results of the metrics are weighted bya contrast sensitivity function (CSF) and, thus, the conditions under which a particularimage is viewed must be speci“ed. This leads to the establishment of a common frameworkconsisting of three components shared by all spatial metrics. First, the RGB image is trans-formed to a color opponent space, separating the luminance channel from two chrominancechannels. Second, associated with this color space are three contrast sensitivity functionsfor each individual opponent channel. Finally, the speci“c viewing conditions, comprisingboth digital displays as well as printouts, are supported through two distinct MTFs.Keywords: Image quality, sharpness, noise, texture blur, MTF, noise power spectrum,contrast sensitivity function