The printed copy of the transmission manuscript is a visual image formed under the action of transmitted light. The reflective manuscript is a visual image formed by the reflection of the manuscript under the illumination of a light source.
The tone of the printed matter is that the colors are classified according to lightness and darkness. The reproduction of printed products should achieve color restoration, tone restoration, texture restoration, and clarity restoration. Color reproduction means that the hue is accurate, and the printed product reproduces the true and perfect color of the original without discoloration and noise.
The ideal tone restoration means that the tone on the manuscript is restored "faithfully" on the printed product to meet the requirements for copying the manuscript. Since the maximum recording density of the printed matter is 1.8, after reaching 1.8, it becomes a straight line parallel to Dt (original density), so it should be adjusted whether it is a reflective draft or a transmission draft, in order to compress the contrast and correct Color difference, reach the range suitable for printing and reproduction tone.
For example: the highest density on the color positive manuscript is Dt = 3.0, and the maximum recording density of the printed matter Dr = 1.8.
It can be seen from the curve that the reproduction of the printed matter cannot reach the highest density reduction of the original, because the materials used in the reproduction of the printed matter include limitations on ink, paper, photosensitive materials (film, PS version), color sequence, and printing machinery. The maximum recording density Dr = 1.8, but when Dt = 3.0, the maximum density of the original is large, and only the contrast can be compressed, otherwise the actual effect will not be printed.
Prints often need to be adjusted when the tone is restored. When the density contrast of the original is greater than the highest recording density of the printed matter, in order for each tone of the original to be displayed on the printed matter, it is necessary to properly adjust the tone reduction. Secondly, in order to adapt to the copy requirements of some special manuscripts (such as photos with light tones and photos with dark tones), certain tones of the manuscript must be properly emphasized, and other tones must be compressed accordingly. The main feature of linear compression is the adjustment of equal proportions of each order. Linear compression does not represent true visual proportional compression, because the DY curve is also nonlinear. After this compression, the bright tone is in the human eye It is not easy to distinguish, resulting in "grey flat" phenomenon.
Tone duplication refers to the relationship between the density of the original and the percentage of duplicate dots
To make all the tone and color on the manuscript can be well expressed on the printed matter, first select the correct gradation curve. Hierarchy is the basis of tone and color changes. If the layers on the screen are not rich, the expression of colors must be monotonous and tasteless. Only when the layers are realistic, can vivid color changes.
It is impossible to copy the originals faithfully, because the density contrast of most of the originals is greater than the density contrast of the printed products, so the copy must compress the density. Therefore, it is necessary to lose some of the subtle levels. In actual operation, the reasonable level curve should be adjusted according to the contrast of the original and the specific content of the tone, that is, the level of the secondary parts on the reflective or transmissive manuscript should be adjusted. Compression is carried out so that the levels of main parts are emphasized and characterized.
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