The Techniques and Key Points of Reproduction (6)

Sixth, black field (dark tone) selection and printing network value setting law

1. The importance of black point selection and setting.

The black field setting is defined as the setting of the printed dot value in the darkest part of the image. Shadow tone is an important part of the image modeling arts. The dark tone selection point setting is used to determine the end point of the tone reproduction, change the dark tone contrast, change the dark tone level, and correct the color shift. The selection point, the correctness of the setting, directly affects the dark tone, the reproduction of the intermediate level, and the contrast effect of the image. Therefore, the dark setting is an important part of setting the tone range.

2. Black site selection, setting the impact on the quality of printed products.

The selection of black sites and the correctness of setting will result in three situations in the quality of printed matter. Figure 6:

(1) When the black point selection and common density values ​​are set correctly, and the maximum printing dot value setting is also correct, all the dark and medium tone information on the original can be correctly transferred to the printed matter without any level loss. The contrast is also ideal. For example, the shaded density value on the reflective draft is 1.90, and the shaded density value on the desktop or desktop scanner is also 1.90, which means that the dark tone information on the original can be reproduced ideally on printed matter. As shown in Figure B line.

(2) If the black field density value is set too small, 1.70, dark tone network value is set too large, dark tone darker, hierarchical parallel, print product contrast is too large, as shown in Figure A line.

(3) If the black field density value is set too large to be 2.10, if the dark tone dot value is set too small, the dark tone becomes lighter and the print contrast becomes smaller, as shown in Figure 6C.

3. Blackground selection, set the five basis.

(1) It depends on the density of the original dark areas.

(2) It depends on the size and level of the area of ​​the original dark tone.

(3) It depends on the density of the main part of the document in the dark tone.

(4) It depends on the type, characteristics, and printability conditions of the original.

(5) According to different processes, it is determined by the gravure printing process.


4. Black field (dark tone) selection, setting of three elements.

(1) Select the correct black field sampling point.

Generally, the black field sample points are selected in the neutral dark part of the original darkest part of the manuscript. There is not much difference between the different manuscripts, but the difficulty of the selection points lies in that one person's ability to recognize dark tone changes is poor. 2 dark tone (especially color reversal film) has a large tolerance, large color concentration, low light transmittance, large color cast, coarse particles, often can not find neutral black parts, often two kinds of situations: It is the dark shadow or dark part of the object as the black field sampling point, set the maximum dot value, resulting in a dark mass in the dark part of the printed product; the second is to use the color cast part of the dark part of the object as a sampling point, such as the blue, to The C version is set at 95%, while the black version is only at 50 to 55%. The operators did not deepen the black version.

, resulting in the black version is too shallow, resulting in insufficient contrast of the printed product, the dark part is not dark, there is no intensity. The correct method is as follows:

A. First analyze the original and determine where the darkest darkest part is in this image. Set the maximum dot value as the darkest and darkest part of the image. In short, any image should have the darkest and darkest parts.

B. The black field sample point should be selected as the neutral black or near neutral black part. It is better to select the black object so that the ratio of the set dot value of the C, M, Y, K color version can be achieved accurately.

C. According to the contrast of the original density, the thickness of the hue, and which subsections the main part is in, the black field density setting value is determined. Otherwise, it will affect the accuracy of setting black network values.

(2) Determine the base black based on the printing process and printability conditions.

The basic black is defined as the maximum dot value that can be printed by the printing. That is to say, in the dark part of the required hierarchy, the maximum dot value that can be printed out by the printing is set, which is called the setting of the base ink. The basic black dot value setting is basically a fixed value. The current offset printing process is:

A. Superior printing paper and other printability conditions can be printed out. The maximum dot value for non-sticking is 97 to 98%, but the majority is 95%. The base black is C95 to 98%, M, Y85 to 88%, K75 to 80%, and the total of four-color dot values ​​is 340 to 360%.

B. General printing conditions such as coating paper, C93% ~ 95%, M`Y80% ~ 85%, K70% ~ 75%, the sum of four color dot value is about 320%.

C. Offset printing conditions such as offset paper, C85 ~ 90%, M, Y75 ~ 80%, the sum of the four-color dot value is about 300%.

At present, the gravure printing process, since the gravure roller nets carved out by the OPP film proofing or printing, the linear scaling of the dot scale is linearly enlarged, the darker the dot network, the increase in ink content, the dot network expansion also more and more quickly. Therefore, the power or desktop scanning color separation should not be long for the gravure roller, and the key value of the dark tone portion should be controlled so as to prevent the OPP film from being proofed or printed. At the same time it will affect the deepening of the tone.

The actual production test, gravure can be transferred out of the best dot value is 90 ~ 93%, the basis of black C90 ~ 93%, M80 ~ 83%, Y80 ~ 83%, K65 ~ 70%, the sum of four-color dot value It is completely 300 to 310%.

(3) Correct black edition setting and adjustment.

The key to the black field setting is the setting and adjustment of the black version. At present, Beijing and most of the country's electricity and desktop system operators do not pay attention to the black version. They do not realize the importance of the black version. When scanning color separation, it seems darker and shallower for the black version. It doesn't matter if the tune is longer or shorter. As a result, many products are produced. One is that the black version is too dark, which makes the image dark and dark. Second, the black version is too shallow, the image has no contrast, there is no intensity. In fact, with a good black version, you can enhance image contrast, enhance darkness levels, make dark areas strong, and have a strong sense of body, which is one of the keys to enhancing image aesthetics and improving image quality.

There are two technical indicators for setting and adjusting the black version:

1 black color adjustment. In the darkest part of the image, how many black dot values ​​should be set properly? Some think that 60 to 70%, some think 80 to 90%, which results in the darkness of the current black version. There is actually a law to follow. of.

A. Theoretically speaking, the highest density of prints needs to be supplemented by a black print. Generally, a print density of 0.3 can be used. However, since the optical add-in is non-linear, the highest print density is not the sum of the print densities of the individual inks. Therefore, the print density of the actual black print should be around 0.50, otherwise the black print will not or cannot fully achieve the role of the black print. The integral density of 0.50 is equivalent to 68% of the dot value, so the black version should keep at least 70% of the dot value in the darkest part of the image, and the best is 75-80%.

B. From the type of manuscript, the content characteristics: * The Chinese painting is dominated by ink, the thick ink part can be set to 85 to 90%, and the indented ink can reach 100%. * Most originals of scenery, characters, black version is set to 75-80%. * A color-originated manuscript of oil paintings, watercolors, and gouache. The black version is set at 70%. * The gravure gravure printing process of food, seed bags, etc., is 60 to 70% black, 65% is better.

2 adjustment of black tone. The adjustment of the length of the black edition, ie the adjustment of the starting point of the black edition, should be determined according to the type of the original and its content characteristics. The black edition is generally divided into short, medium and long tunes. The black standard curves of the electrophoresis and desktop scanning color separation are short-cut skeleton black editions, and the black highlights originate from 50% of the C edition. As shown in Figure VII: This type of curve does not fully exploit the full-scale contouring effect of the black version. Therefore, it is better to use the medium tone black edition instead, and extend the highlight of the black edition to 35% of the C edition at the black spot. As shown in Figure 8: This is very favorable for lightening, mid-level adjustment, and gray stabilization. A type of manuscript of Chinese painting, the starting point of the highlight of the black version can be extended to 5 to 10% of the C version.

The effective use of the black version is not just a simple addition of black to the three primary colors. The technical method is to match the UCR, and the amount of the three primary colors should be reduced in the black portion in order to make room for a more uniform black plate. Use dark editions to darken levels and use black editions to enhance image contrast.

At present, most of the original document removal amount is 20%, after removal, the dot value is about C75%, M, Y65%, K90%, and the sum of four-color dot values ​​is about 290 to 310%.