Analysis of Image Design Skills in Packaging, Decoration and Printing (Chinese)

2. How to deal with the issue of hierarchical density

Reflective manuscripts, such as color drawings, prints, and photographs, have relatively close contrasts in the density of layers. However, the overall density and contrast of color-transmitting documents are quite different. In general, the density contrast is between 1.8 and 2.4, which is an ordinary manuscript. It is higher than 2.4 for high contrast and less than 1.8 for low contrast. 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. For manuscripts with different levels of density and quality, the processing method differs depending on the manuscript.

(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.

(2) Ordinary 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.

(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. The level reproduction and reproduction curve can be adjusted according to different levels of the image level distribution.

(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.

(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 main body of this type of 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 levels are 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. For copying of this type of manuscript, the density of the black and white field calibration standard should be larger, and the level curve of the medium and dark tone should be slightly reduced, and the level of the medium brightness tone including the subject tone should be reproduced more brightly. Make the reproduction of the picture clear, but also stressed the dark tone of the secondary differences, in order to achieve better tone contrast and visual brightness effect.

(6) Different manuscripts are distributed at the midtone level. Some manuscripts with medium-to-dense contrasts have fewer intermediate tone levels, a greater density difference, and high and low tone levels, such as color films shot against the light, should be designed to adjust the level of darkness of this type of image subject. Good copy reproduction effect can be achieved. The level contrast of the image can be used as the density range compression adjustment when copying. The height of the initial density can also be changed by setting the high optical density and adjusting the recording settings. However, whether the distribution of the original image hierarchy can meet the artistic requirements requires that the level distribution be compressed and the redistribution adjustment should be made. The depiction and analysis of manuscript level distribution is crucial to the redistribution adjustment of level reproduction and is the primary basis for level reproduction. The contrast range of transmission originals varies greatly, and color prints have to be reproduced as a screen with a substantially uniform density range. This density range is mostly lower than the density range of color originals. In the separation and printing process, compression adjustments must be made. What kind of redistributive adjustments are taken at each tone level depends, on the one hand, on the distribution of the tonality levels of the manuscript, and at the same time it relates to human visual perception. Among them, both the Munsell brightness value of the visual response and the subjective factors of people's visual psychological requirements. To adjust and copy the original tonal hierarchies, it is necessary to sum up the people's visual psychological needs, add the physical values ​​of the visual response, and then consider the distribution of the original levels to obtain the density reproduction curve of the print screen. The evolutionary data in the process of copying and reproduction is designed to design a tone reproduction curve of a specific manuscript. The density of printed matter is so large that it can not only reproduce the level of some manuscripts or original scenes, but also make it possible to open up some contrasts between levels and levels, and the sense of three-dimensionality is also strong. In particular, the subtle contrasts can be enhanced and the clarity of the image hierarchy can also be enhanced. On the other hand, it also makes the color of the picture open, which makes the deeper saturated, the shallower brighter, and enhances the three-dimensional color. However, the increase in the density of the printing ink layer is inconsistent with the dot gain, and it is impossible to achieve such a high density as a color transparency sheet. Only under the excellent conditions such as the adaptability of paper, ink, and equipment, and the precision of the printing press, can have lower dot gain value and higher ink layer density. Therefore, the objective technical standard for determining this quality index is to use a color reflection densitometer to measure the printed solid density of each printing ink layer and the printing density of 75% dot, and calculate the printing K value. When there is a higher printing K value (yellow 0.3 to 0.4, magenta and cyan 0.4 to 0.55, and black 0.5 to 0.6), their respective field densities High, and when the overprinting efficiency of each ink layer approaches 90%, the tone of the printed matter is also better. Such printed matter must be clearly structured, full and full of three-dimensional images. In order to save printing ink, some people advocate reducing the density of the printing ink layer to reduce the dot gain. In this way, although the number of printed dot adjustments is reduced, the leveling of the dark tone end of the image is reduced, but the overall tone contrast is not the highest. , also can not reach the best level of print tone reproduction.

As the printing process tone is non-linear, compensation adjustments should be made before printing. The network tone adjustment is limited by various conditions during the process of printing and printing, and the transmission of the tone network is non-linear. In order to adapt the printing process, compensation adjustments must be made. The key point is to make adjustments to the three outlets of the printing area, which are also called three key areas, namely 3%, 50%, and 80% outlets. Because 3% small points are easy to lose, it will affect the color level of the highlight area, 50% of the dot area will easily increase, affecting the midtones, changes in the color of the special characters, 80% of the dot area will be easy to merge, affecting the tone level, especially It is the dark color of the main color and the deep color of the same level, so that it is difficult to balance the two, often at a loss. Therefore, for some important colors and important parts of manuscripts, they are adjusted so as to avoid these three dot skip areas, thereby providing an ideal printing plate for printing, making it printable, and printing a good product.

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