Fine adjustment of color gradation at the beginning of printing

Printed manuscripts require four-color electrical division for plate making. Apple computer color separation manuscripts include reflective drafts (such as: color pictures, drafts, watercolors, oil paintings, Chinese paintings, new year paintings, gouache, etc.) and transmission drafts (such as: color reversal films (natural color positive films), color negative films, etc.) The lightness and darkness on the color negative manuscript is opposite to the original scene, and the colors are complementary to the original scene. For example, the opposite color of magenta complementary on the negative film is green; the opposite color of yellow complementary is blue-violet; and the complementary color of red is cyan. The lightness and darkness on the positive manuscript are the same as the original scene, and the colors are exactly the same as the original real scene.

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 is necessary to adjust both reflective and transmissive manuscripts in order to compress contrast and correct chromatic aberration to achieve suitable The range of printing and copying tone.

For example, the maximum density on a color positive document 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 reach the highest density reduction of the original, because the materials used in the reproduction of the printed matter include ink, paper, photosensitive materials (film, PS-plate-), color sequence, and printing machinery. Limit, 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.

Tonal duplication refers to the relationship between the density of the original and the percentage of dots copied.

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.

Under the premise of normal contrast of color manuscripts, adjust the gradation curve correctly according to different types of manuscripts. The level control of the Apple extension and color separation Apple computers is both convenient and flexible. It can be locally strengthened or compressed, but it is necessary to pay attention to the balance of the dichroic gradation curve. The neutral gray balance should be appropriate. The incorrect gradation curve will distort the replica. Therefore, we must pay special attention to the correct use of gradation when operating the electrical extension and Apple computers, but the color cast of the original can be corrected by adjusting the gradation curve.

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