Different brands and specifications of inks, printed on different substrates, can achieve different field density and different dot expansion. Therefore, in actual production, we should determine the best field density and appropriate dot expansion value for different substrates and different inks

Different brands and specifications of inks, printed on different substrates, can achieve different field density and different dot expansion. Therefore, in actual production, we should determine the best field density and appropriate dot expansion value for different substrates and different inks

This paper discusses the method of using printing contrast to determine the best field density and dot expansion

Printing contrast or K value refers to the comparison between field density and dark tone density (mainly 75% or 80% density). The greater the printing contrast value, the more levels it can reproduce, and the richer the details of dark tone; On the contrary, the smaller the printing contrast value, the fewer levels it can reproduce. The calculation formula is:

In the formula, DS is the field density value (including paper or minus paper density), and DT is 75% or 80% density value (including paper or minus paper density)

It can be seen from the formula that if the DS value of a printed matter is as large as possible and the DT value is as small as possible, the printing contrast can be maximized

Of course, if DS and DT are measured directly and then calculated, it is cumbersome. Therefore, the general spectrodensitometer has the function of directly measuring printing contrast

For four-color printing, field density is an important factor affecting color reproduction. The field density determines the thickness of the ink layer to a certain extent, as well as the dot expansion of the printed matter and the tone reproduction of the printed matter. In general, the level of the original is relatively rich, such as photos. After being copied into printed matter, the level will be lost and compressed. If the field density is too small, the reproduction ability of the level is low. Therefore, it is necessary to increase the field density value and minimize the compression of the level, so as to improve the step reproduction ability; However, if the field density value is too high, the dot expansion will be too large due to the too thick ink layer and the influence of printing pressure, which will also cause the loss of layers, especially the dark tone layers. Therefore, controlling the field density is very important for the replication of the whole tone