The color rendition of a halftone image depends on, among other things, physical and optical dot gains and fluorescence of substrates. A unified model describing spectral reflectance of a print is proposed with consideration of these effects. In this model the effects of either physical or optical dot gain are characterized by a single parameter, while those of fluorescence by two sets of spectral parameters, one for fluorescence of bare paper and one for fluorescence of a print solid. This model is tested and further illustrated with applications to images generated by a laser color printer on ordinary office papers.