Pre-press printing

Printed manuscripts require four colors for plate making. Apple Computer's color separation manuscripts have reflective drafts (such as: color pictures, drawings, watercolors, oil paintings, Chinese paintings, new pictures, gouache paintings, etc.) and transmissions (such as: color reversal film (natural color positive film), color negative film, etc.). The color negative original is darker than the original, and the color is complementary to the original scene. For example, the complementary color of magenta on the negative film is green; the complementary color of yellow is blue-violet; the complementary color of red is blue. The brightness of the original document is the same as that of the original scene, and the color is exactly the same as the original real scene.

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.

Under the premise of normal contrast of the color draft, the level curve is correctly adjusted according to different types of originals. The computer control of the extension and color separation of Apple Computer is convenient and flexible. It can be partially enhanced or compressed, but it is important to pay attention to the balance of the color separation layer curve, the neutral gray balance should be appropriate, and the incorrect level curve can distort the reproduction. Therefore, special attention should be paid to the correct use of the hierarchy when operating the extension and the Apple computer. However, the entire color cast of the original document can be corrected by adjusting the level curve.

When compressing the contrast of the original gradation, generally, the following method is often used to compress certain parts.

1 Under normal circumstances, normal manuscripts should be properly contrasted and should be compressed to a low level, especially when emphasis is placed on emphasis on mid-level and on-tone levels.

2 The manuscript is boring, and the tone of the manuscript is adjusted. If emphasis is placed on the level of tone and midtones, the intermediate tone level will be leveled accordingly.

3 The contrast of the manuscript is boring and the whole picture has a large low-key area, and the low-key level should be opened, but the middle tone level appears dull.

4 The level of the middle tone of the manuscript is relatively flat, and the contrast is small. The level of the tone can be compressed and the contrast between the middle tone levels is greater.

5 The manuscript contrast is basically suitable for printing and copying. It is based on the image of the middle tone. The area of ​​the dark tone is smaller, and the tone level can be compressed to emphasize the middle tone level.

6 Color photographs are often encountered. These documents are thin and have low contrast. For these originals, the levels of the bright and dark tone can be compressed to make the contrast in the middle tone level larger.

7 The level of flatness of the original highlights is low and the contrast is small. The tone level can be opened, but the level of the midtones is flat.

Transparency of the natural color film is relatively large, about 3.0, usually under the need to compress the contrast, to meet the requirements of print reproduction; and the manuscript of the reflection of the contrast is relatively small, the original nausea, according to different The original features are brightly copied. Such as the copy of the portrait of a person's portrait is the color of the character, y, m is the key; landscape reproduction is the focus of natural scenery, y, c color is the main point. Flexible use of level travel buttons to adjust to a reasonable level of the curve, to correct the deficiencies of the original, to maintain the main part of the corresponding loss of the secondary part, boldly choose, try to make a good copy. However, if the adjustment of the level curve is unreasonable, it may result in the inversion of the primary and secondary images, the unclear level, and the inaccurate hue.

The color reproduction of printed matter is mainly due to the lack of basic colors and the disadvantage of excessive colors. In order to reproduce high-quality printed products, basic colors should be deeper without losing layers. The basic color should reach 100%, the basic color should be full, the basic color should be moderate, and the basic color can not be lost.

The opposite color should be appropriate. Because the purity of the ink in the current market is not bright enough, the hue and transparency are poor, the whiteness of the paper is poor, and the smoothness is poor. Therefore, when using the color, it should be noted that the more vivid color complementary color (contrary color) is smaller and stronger. Complementary color at the color to be used, the brightest at a small area of ​​color complementary color can not, so play a role in color changes and set off the level, can be used properly to make the basic color more vivid, thick, rich colors realistic.

The color reproduction of a printed matter is actually the additive color reproduction of the three primary colors y, m, and c of the color material with the subtractive color as primary color light. The three primary colors of y, m and c colors are the basic three primary colors of all the colorful changes. The black version cannot afford any color change. The black version only stabilizes the gray balance, plays a skeleton role on the color image, makes the dark tone darker, emphasizes low-key levels and outlines, and enhances the thickness and three-dimensionality of the picture. The three primary colors of y, m, and c pigments transition to a black field, that is, y+m+c=approximately black. A portion of the neutral hair base color (tricolor) formed is removed from the three primary colors of y, m, and c and replaced with black ink. This is how the UCR is used for electrical extensions and Apple computers. Background removal has many necessities: 1 Improving the adaptability of printing, generally used in shadows, in the dark tone area, if three primary colors are used for printing, the dot area is often very high, and the ink layer is easily generated during high-speed multi-color printing. Too thick and paste version and other issues. If the background color is removed, the amount of ink will be greatly reduced, mainly saving the amount of y, m, and c color inks, and improving printability. 2 conducive to the control of neutral gray balance.

The length of the black version depends on the amount of background color removal of y, m, and c colors. The amount of background removal is large. The midtones and dark tone levels are flat. The black version can be used to lengthen the tone to compensate for the loss of the three-color version. The level. If the removal of the three-color version is very small, the black version of the tone can be reduced appropriately to avoid the middle tone nausea. The dark tone is generally scaled with the maximum density of the image, and the image tone is mainly satisfied. According to the characteristics of the original document calibration, pay attention to the dark color balance, while the dark tone calibration should also consider the relationship with the removal of the base color (UCR).

(Source: Chinese print community)