Determining the best solid density using print contrast
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For four-color printing, solid density is an important factor affecting color reproduction. The density of the field determines the thickness of the ink layer to a certain extent, and also determines the dot enlargement of the printed matter and the tone reproduction of the printed matter. Under normal circumstances, the original is rich in layers, such as photos, and after being copied into printed matter, the level will have some loss and compression. If the density of the field is too small, the reproduction ability of the hierarchy is low, so the density of the solid density is increased, and the amount of compression of the layer is reduced as much as possible, thereby improving the tone reproduction ability; however, if the density value in the field is too high, since the ink layer is too thick, and The influence of printing pressure, causing the expansion of the outlets to be too large, will also cause the loss of the hierarchy, especially the partial adjustment of the dark tone. Controlling the density of the field is therefore critical to the replication of the entire tone.
However, inks of different brands and different specifications are printed on different substrates, and the density in the field can be different, and the dot enlargement is also different. Therefore, in actual production, it is necessary to determine the optimum solid density and the appropriate dot gain value for different substrates and different inks.
A method for determining the optimum solid density and dot gain using print contrast is discussed herein.
Print contrast or K value refers to the contrast between solid density and dark density (mainly 75% or 80% density). The greater the contrast of the print, the more layers it can reproduce, and the richer the details of the dark tone; conversely, the smaller the print contrast, the less the level of reproduction. Its calculation formula is:
K = (Ds - Dt) / Ds =1 - Dt / Ds
In the formula, Ds is the solid density value (which can be paper containing or minus paper density), Dt 75% or 80% density value (can be paper containing or minus paper density).
It can be seen from the formula that if the Ds value of a certain print 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 cumbersome. Therefore, the general spectrodensitometer has a direct measurement of the contrast function. The following example analyzes the relationship between the printing contrast and the solid density.
Printing an ink on a coated paper, gradually increasing the amount of ink, measuring the contrast of each ink, and measuring Ds and Dt simultaneously.
It can be seen that when the solid density Ds = 1.60, the printing contrast value is the largest (K = 44%), so the optimum solid density should be 1.60. Then, the measured dot gain is increased, and the dot gain value at 25%, 50%, and 75% is 8%, 18%, and 10%. When the solid density Ds<1.60, the reproduction ability of the tone level is low; conversely, when the solid density Ds is >1.60, the dark point of the dot adjustment causes the printing to decrease and the loss level.
Therefore, for this ink and this paper, the solid density should be set to 1.60, and the dot gain points at 25%, 50%, and 75% should be 8%, 18%, and 10%. At this time, the level of compression is the least, and the tone reproduction is the highest.