Abstract: A histamine concentration level of a fish item is determined by illuminating the fish and analyzing the resulting spectral image data. Specifically, an algorithm is applied to the fish image data so that a histamine concentration value is calculated for every pixel of the fish image. A corresponding histamine concentration image of the fish is produced based on the collective histamine concentration values. The fish is accepted or rejected based on the collective histamine concentration values and/or the histamine concentration image. The histamine concentration image may be used to identify specific parts of a fish fillet that exceed (or do not exceed) a predetermined histamine concentration level.

Abstract: A multi-spectrum, multi-channel imaging spectrometer includes two or more input slits or other light input devices, one for each of two or more input channels. The input slits are vertically and horizontally displaced, with respect to each other. The vertical displacements cause spectra from the two channels to be vertically displaced, with respect to each other, on a single image sensor on a stationary image plane. The horizontal displacements cause incident light beams from the respective input channels to strike a convex grating at different respective incidence angles and produce separate spectra having different respective spectral ranges. A retroflective spectrometer includes a convex grating that, by diffraction, disperses wavelengths of light at different angles and orders approximately back along an incident light beam. A single concave mirror reflects both the input channel and the dispersed spectrum.