In this thesis spectrophotometric measurements of the choosen paper substrates and coloured prints have been performed. The prints were obtained by classical offset, amplitude and frequency screen modulation, for primary colours CMYK. The optical values which characterize the printing surfaces and prints such as scattering and absorption were investigated according to Kubelka-Munk theory, while the lateral scattering is the appearance which is described by the Yule-Nielsen parameter n. Kubelka-Munk theory has been used successfully for a long time because the basic optical values of the printing surfaces and coloured prints, opacity, scattering and absorption are described by reflectance and transmission which are experimentally determined very precisely and simply. Conservation of photon energy suggest the Murray-Davies method, photon flux add linearly, but the reflectance predicted by Murray-Davies equation is generally higher than the measured reflectance. Yule and Nielsen correct Murray-Davies equation adding photon flux by power factor of 1/n and in that way describe lateral scattering. The fundamental cause of optical dot gain is lateral scattering of light within paper. Light that enters the paper between the halftone dots can scatter laterally within the bulk of the paper before returning to the surface as reflected light. This lateral scattering in the bulk of the paper increases the probability the light will encounter a halftone dot and be absorbed. Thus the effective absorption cross section of the halftone dot is larger than the physical size of the dot. The obtained experimental data of the reflection spectra were processed mathematically in order to obtain the necessary data for calculation of the physical values according to the suppositions of the used theories. Mathematical processing of the experimental data was performed by means of the programs MathCAD 2002 Professional and Data Analysis and Technical Graphics Origin 6.0. According to all the mentioned, it is important to connect the Yule-Nielsen parameters n, as the measure of the lateral scattering, with the fundamental physical and optical parameters of the system in order to foreseen the size of the optical dot gain. These physical, i.e. optical parameters are scattering and absorption of Kubelka-Munk theory. On the basis of the experimental measurements and mathematical results the area of the application of the mentioned theories in regard to the real conditions of the graphic reproduction has been determined and the correlation among the relevant parameters has been established.