Four-color printed field density

For four-color printing, density in the field is an important factor affecting color reproduction. The density of the ground determines the ink ink layer thickness to a certain extent, and at the same time it also determines the enlargement of printed dots and the reproduction of the print. Under normal circumstances, the manuscript is rich in levels, such as photographs, and after being copied into prints, the levels will have some loss and compression. If the density in the field is too small, the level of reproduction capacity is lower, so the field density value should be increased to reduce the level of compression, thereby improving the ability to reproduce the tone; but if the field density value is too high, due to the ink layer is too thick, and The influence of printing pressure will cause the network points to expand too much, which will also result in loss of levels, especially in the dark tone. Therefore controlling the density of the field is crucial for the reproduction of the entire tone.

However, different brands, different specifications of ink, printed on different substrates, the field density can be achieved are different, the dot expansion is also different. Therefore, in actual production, it is necessary to determine the best on-site density and appropriate dot gain values ​​for different substrates and different inks.

The method for determining the optimum solid density and dot gain using printing contrast is discussed here.

Print contrast or K value refers to the contrast between solid density and dark density (mainly 75% or 80% density). The greater the print contrast value, the more layers it can reproduce, and the richer the details of dark tone; conversely, the smaller the print contrast value, the less the level it can reproduce. Its calculation formula is:

In the formula, Ds is the solid density value (which can be paper-containing or minus paper density) and Dt is 75% or 80% density value (which can be paper inclusion 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 print contrast can be maximized.

Of course, if Ds and Dt are directly measured and then calculated, it is more complicated, so the general optical densitometer has the function of directly measuring the print contrast.