scene intensity measuring and illumination source detection apparatus for determining scene illuminant and appropriate exposure settings for an image capture device is disclosed . the apparatus includes a diffractive optical element including an off - axis segment for dispersing incident scene illumination into its spectral components and for focusing the incident scene illumination , a structure responsive to the spectral intensities of the spectral components of the incident scene illumination for producing detection signals corresponding to such spectral components , a structure coupled to the sensing means for producing digitized detection signals , and a structure responsive to the digitized detection signals for determining the scene illuminant and the appropriate exposure settings for the image capture device .