3.3.2. SUBTRACTIVE FLOWER EQUALIZATION

The scheme of experiments on subtractive color equalization is shown in Fig. 3.3.3. Light with spectral density consistently passes through three filters - cyan, magenta and yellow. The spectral absorption curve of each dye depends on its concentration. It should be noted that the absorption curves of the dyes used in practice change in a nonlinear manner as their concentrations change.

In the first stage of the subtractive adjustment process, the dye concentrations of the three filters change until a subjective adjustment of the reference white color is achieved. . These concentrations are equalizing values. , , . Concentrations are then adjusted to equalize the desired color. . Found concentrations - equalizing values , , - used when calculating coordinates , , according to the relation (3.3.1). Obviously, there is no fundamental difference between additive and subtractive color equalization. In the subtractive system, the yellow dye acts as a variable absorber of blue light, i.e., controls its intensity. In the same way, the magenta filter controls the green, and the cyan - by the red light. These filters are broadband and transmit a lot of light. Therefore, they are more convenient to use in subtractive systems than narrowband red, green and blue filters.

Fig. 3.3.3. Subtractive color adjustment.

Conventional dyes do not have a wide range of density changes. In order to increase the contrast of the reproduced image, a fourth filter layer — neutral gray — is often introduced into the printing industry. Subtractive reproduction of colors with real dyes with overlapping absorption curves is discussed in Chap. sixteen.