When using trichromatic printing, stencil control is especially important. Since the inks have a certain degree of transparency (especially UV inks), and the deviation of the stencil leads to a change in the thickness of the printing ink film, the printing color is significantly shifted. This color shift can be described by the absorption of light by the ink film (ie optical density). The optical density can be measured using a densitometer to measure the printed color. Measurement results are displayed in logarithmic form. It can also be said that this figure represents the ratio of the light absorbed by the "absolute" white material to the light absorbed by the test ink. "Normal ink volume" is a term used to describe the correct optical density printed with a particular ink and substrate. By using a densitometer to measure prints that are more accurate (colors appear visually correct), the results can be used as a reference for printing or proofing under the same ink and substrate conditions. Using this method, you can perceive the change in color and adjust it instantly to ensure that the print quality is maintained within acceptable latitude.