Photometric specification of images

The traditional perspective on specifying a stimulus' luminosity is to measure its emitted light. Because viewing is the reverse of radiating, an alternative approach measures the light as it is received by the eye or other image sensor–incident photometry. From this perspective, I develop a method of specifying stimulus luminosity in terms of the flux incident on noncontinuous detector surfaces whose sensing units map the directional characteristics of an image. Sensing unit size determines how much of the image at its location induces its sensory response. That portion of the image is the sensing unit's receptive field. Since sensor response depends on rate of photon impingement, the appropriate photometric measurement is lumens-per-receptive-field (lm/rf). 'lm/rf' accounts for pupil area and can be corrected for ocular transmittance. Photometry of images can be completed by specifying the light attenuation needed to reach the sensing system's response threshold.