In the field of packaging and printing, color printing of plates has become the mainstream of printing. The quality of printed matter is also increasing. A picture with beautiful print quality will give people a comfortable and natural feeling, making people feel like they are in the real world. However, due to the influence of subjective and objective factors, although the quality of color printing products has greatly improved over the past, on the whole, there are not many quality-grade products, and they cannot be compared with foreign quality products. These include objective factors such as equipment and materials, but the quality of operators and technical deficiencies are also important factors. We know that the quality of color printing products is constrained by all the factors involved in the copying process, such as the tone levels, color tone, and sharpness quality of the color original image; the color separation screening picture tone levels, colors, and sharpness Emphasizes the accuracy of the data such as copying and adjustment; the amount of change in the intermediate process dot-changes such as copying and printing, and the degree of stability; the ink layer density, dot gain value, or printing relative contrast data of the printing (or proofing), and the degree of control stability; Overprinting efficiency of each color ink layer, tone evolution, color balance and gray balance reproduction; performance applicability and operation adaptability of printing paper, color characteristics and operational applicability of ink; equipment, equipment and materials for each operation process The printability, the quality of the process operation, and the adjustment of the data for copying the object are many aspects.
Among the above-mentioned influencing factors, the quality of pre-press image production directly determines the quality of color printing products. Therefore, when making images before printing, if the quality of the originals is found to be poor, corrective measures should be taken to improve the quality of the printed matter. As most of the original manuscripts are now available, most of them have some deficiencies. If pre-press production personnel do not have a high level of technology and do not have a good aesthetic aesthetic, it is very difficult to produce high-quality products. Briefly introduce some techniques and methods for processing defects in the quality of originals in prepress image production.
The method of dealing with the problem of the original tone level
Reflective manuscripts, such as color drawings, prints, and photographs, have relatively close contrasts in tone density. However, the overall density and contrast of color-transmitted texts are relatively large. In general, the density contrast is between 1.8 and 2.4, which is the original manuscript. It is higher than 2.4 for the high contrast manuscript and less than 1.8 for the low contrast manuscript. The initial density of 0.3 to 0.5 is the normal draft; those above 0.5, regardless of the size of the contrast, are due to insufficient exposure (or development), and are boring originals; the contrast is lower than 1.6, and the initial density is lower than 0.3, which is caused by excessive exposure (or development), is a thin original.
The overall density and contrast of color-transmitting manuscripts are closely related to the illumination conditions of the manuscript, the exposure, and the development process. The segmentation of the image on the photosensitivity curve is different, and the contrast in the density of the layers is also changed. Its level of distribution varies. For the photographic art manuscripts, the aesthetic adjustment is based on impressions and visual effects, emphasizing the contrast effect of the pictures, highlighting the sense of light, emphasizing color saturation, doing some exaggeration and rendering on the important colors in the picture, highlighting the color visual impact. It is necessary to emphasize some of the deficiencies in making up for the shooting and the rinsing process, and to adjust and deal with the relationship between color, light, shadow, light, darkness and space in the photographic art, highlighting the styling effects such as color tone, atmosphere, light and shadow, and texture of photographic images. Make the manuscript has a strong sense of light, bright light, dark tone with intensity, give people the feeling of light and shadow beauty; have a strong color saturation, bright color, rich color changes, give people a color art appeal; have a high Sharpness, scenery, clear material, delicate particles, rich levels, giving a sense of reality. In actual production, the black color of the object is not pure due to the dark color of the photographic image. Therefore, the UCR/UCA function is used to correct the bias, so that the trichromatic version achieves a neutral black effect, and then the black version is dominant, so as to achieve a pure black effect and a better expression of the texture level of the black object.
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. However, we must pay attention to the balance of the color separation layer curve, the neutral gray balance should be appropriate, and the incorrect level curve will distort the reproduction. For the entire color cast of the original, it can generally be corrected by adjusting the level curve. For originals with different levels of density and quality, the following methods are often used when compressing the contrast of originals.
(1) Normal exposure and density contrast standards. The main parts are in bright and medium tone, and it is proportional to the brightness. It belongs to the best visual brightness range and is in the 4th to 6th level of the new system of brightness. This kind of manuscript black and white calibration is based on standard density values. As a result, all the information on the original and middle notes of the original can be reproduced on the scanning color separation sheet. Normal manuscripts have moderate contrasts, and they should make the low-profile levels even. In particular, when it is necessary to emphasize the middle tone and the tone level, it is more appropriate.
(2) Medium contrast originals. The low density is 0.3-0.5, the high density is 2.4-2.8, and the contrast is common. Near the standard manuscript, the high and low profile levels of the image can be expressed in the straight part of the photosensitive characteristic curve, with rich layers of intermediate tone, and the main level is in the middle light. Adjustment, leveling density level difference and the original scene is proportional, the tone is generally more normal, while the original contrast tone compression, according to the tone level of the tone reproduction curve close to the standard level adjustment, can achieve a good copy effect. Due to the different distribution of levels of the original tonal hierarchy, the same is the original in contrast, and the reproduction curve of the tone level should also be different. If the manuscript is clear, the subject is adjusted within the bright midtones, and the copy should be slightly deepened to satisfy the visual response. If it is a thick-tune manuscript, the subject tone is often within the medium-density range and should not be deepened. The reflection draft (except for photos) level reproduction curve can be between the above two. For the contrast of the manuscript, which is basically suitable for printing and copying, the photograph with the main tone of the middle tone has a darker tone area, and the tone level can be compressed to emphasize the level of the intermediate tone.
(3) High contrast originals. High optical density of not more than 0.4, but the highest density of more than 3.0 manuscripts, mostly the contrast of the original contrast of light and shade is too large, the general middle tone level rich and complete, the ratio of the brightest and darkest areas is not large, generally not At the main level, only high- and low-key density jumps and increases the contrast. This type of manuscript, when selected for highlights and shadows, can generally be rounded off at both ends of the secondary level, in order to reduce the scope of its tone reproduction. Its level reproduction and reproduction curve can be adjusted according to different levels of the image distribution curve.
(4) Low contrast originals. The gradation contrast is below 1.7, and the low light density original document with a high optical density of 0.3 or less is often caused by overexposure or excessive development. Its main part is bright and thin, with high lightness. It is at the 7th and 8th grades of the new system of lightness. Most of the lighter midtones fall on the shoulder of the negative image characteristic curve. The brightness adjustment level is rich, but the density difference is small. , And a large proportion of the area. Make a deeper copy when making, to reduce the brightness, and approach the standard brightness. This kind of manuscript needs to strengthen the reproduction and redistribution of levels in the bright mid-tones, and the black and white field calibration density values ​​should be smaller. The light curves of the middle and middle tone levels should be slightly deepened to achieve better levels of contrast and visual brightness. The shape of the curve should be distributed according to its level, and its main body should be adjusted to be in bright or medium density range. At the same time, it is also necessary to use deepened and lengthened black edition to complement, so that the intermediate level of reproduction and reproduction is deeper than the level of the manuscript and meets the artistic requirements of visual psychology. If the original color photo is thin, the contrast is small, and the contrast between the middle tone level can be made larger by compressing the light and dark tone levels.
(5) thick stuffy manuscript. High-density light sources with a density of 0.5 or more, or even more than 1.0, are often caused by insufficient exposure or underdeveloped images. Most of the image darkness levels fall on the toes of the negative image characteristic curve and the lower half of the straight line. The manuscript is thick and boring. The whole picture has a large low-key area and the bright tone appears to be flat. If emphasis is placed on the level of tone and intermediate tone, the intermediate tone level will be dull accordingly. For the middle level of the manuscript, the level 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.
The thick main part of the manuscript is darker and darker, and it is located in Levels 2 and 3 of the Shinsei Shinbiao System. There are few bright tone levels, and the dark tone level is rich and the level difference is soft, and the area ratio is large. In the mid-range density range, the reproduction should be reduced by increasing the lightness in order to brighten the brightness and approach the standard lightness.