光学的ドットゲインの物理

抄録

Fundamental aspects of optical dot gain are described. Taking into account multiple internal reflections, we first derive a general, mathematical expression for optical dot gain in the same method as that of F. R. Clapper and A. C. Yule. Among the four parameters used, i.e., ink transmittance T_d, paper transmittance T_p, and reflectances of the front and back surfaces of paper R_f and R_b, T_d and R_f have dominant effects on optical dot gain. The derivation also leads to a conclusion that the famous Yule-Nielsen index n may, under practical conditions, easily exceed 2, which cases have often been attributed to the non-ideality of dot patterns. Then, there is shown that density measurements on photographically produced, ideally hard and perfectly noiseless halftone tints support the above conclusion. Finally, researches on optical dot gain in the past are briefly reviewed.