The printed copy is a visual image formed by the transmitted light. The reflection draft is a visual image formed by the reflection of the original under the illumination of the light source.
The tone of printed matter is the classification of color according to the degree of shade, and the color reproduction, tone reduction, texture restoration, and resolution reduction are required in the reproduction of the printed product. The color reproduction is accurate in hue, and the reproduced printed product truly reproduces the original color perfectly, without color cast or noise.
The ideal tonal reduction is that the tonality on the manuscript is faithfully restored on the printed product and reaches the reproduction requirement of the original. 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 both the reflective draft and the transmitted draft must be adjusted in order to compress the contrast and correct it. Chromatic aberration, to reach the range of print reproduction tone.
For example, the highest density on a color positive original is Dt=3.0, and the maximum recording density of printed matter is Dr=1.8.
It can be seen from the curve that the reproduction of the printed matter cannot be restored to the maximum density of the original, because the materials used in the reproduction of the printed matter include restrictions on the ink, paper, photosensitive material (film, PS plate), 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, only the contrast can be compressed, otherwise it will not print the actual effect.
Prints often require adjustments to tone when the tone is restored. When the density contrast of a manuscript is greater than the highest recording density of a printed matter, in order for the various tonality of the manuscript to be manifested on the printed matter, it is necessary to make an appropriate adjustment to the reproduction of the tone. Second, in order to adapt to the reproduction requirements of certain special manuscripts (for example, photographs that are primarily highlighted, and photos that are primarily dark), some of the manuscripts must be properly emphasized, and other adjustments must be made. The main feature of linear compression is the adjustment of equal proportions of each tone segment. Linear compression does not represent true visually proportional compression because the D-Y curve is also nonlinear. After this compression, the luminance is adjusted to the human eye. It is not easy to identify and produce a "gray" phenomenon.
The reproduction of tone refers to the relationship between the density of the original and the percentage of copying points
To make all the tone and color on the manuscript well represented in the printed matter, first select the correct level curve. The level is the basis of tone and color change. If the level is not rich on the screen, the color performance must be monotonous and boring, and only the realistic level can have vivid color changes.
It is impossible to faithfully copy manuscripts because most of the manuscript density contrast is greater than the density contrast of the printed matter, so the copying of the printed matter must inevitably compress the density. Therefore, it is necessary to lose some of the finer levels. In practice, the reasonable level curve should be adjusted according to the contrast of the original and the specific content of the tone, that is to say, whether it is a reflection draft or the level of the minor part above the transmission document. Compression is made to emphasize the emphasis and specialization of the main site hierarchy.