Technical points of packaging and decoration printing image design II

Second, the lack of manuscript processing

1. Color cast processing method

The true condition of different original tones can be observed more intuitively from the measurement of the three-color density contrast of the original and the depiction of the tri-color density curve. The most popular method of dividing the density range in the color printing reproduction process, which divides the entire density range of the original and the replica into four segments, ie, the entire density range between the highlight spot (white field) and the dark tone spot (black field). Divide into bright (also known as high-profile), middle tone and dark tone of the three segments, and the area less than the high light density is called extremely high light. There is also a five-segment density range, that is, in the above-mentioned four segments, an area with a darker density than the above is also called extremely dark. In the analysis of the original color quality, if the original three-color density and contrast are basically the same, indicating that the original is not color cast, the tone is basically normal. If the tone is complete, the levels are rich, and the distribution is reasonable, even if the total contrast is slightly different, it can be considered a normal manuscript. The color reproduction can be corrected with the normal color error data, and the emphasis is on the reproduction of the tone level. If the three colors of the original document have different densities, it means that one of the colors is biased, and when the contrast of the three color densities is substantially equal, the color is balanced, which is caused by the color fog. This partial color draft, the general tone level is also better, you can change the color separation picture high and low profile three-color dot record settings, and with the adjustment of the level adjustment to achieve full gray balance to eliminate image color cast. However, it is better to design a hierarchical replication curve that adjusts the balance of three-color gray according to the three-color density curve, so that the tone of the full-tone tone can be uniformly corrected. If the difference between the highlights of the original three-color density is relatively large, the three-color density of the dark tone is nearly the same, and the color cast is mainly displayed at the end of the high-profile region, which is unfavorable for high-level reproduction of the image. Although this kind of color cast can directly use the original color shift highlight point as the white balance and input calibration of the color separation machine, the input balance of the color separation machine is changed, but the color correction signal is also changed, and the high light to be retained is retained. Color also lost, data

Often inaccurate. It is better to design the tri-level version of the level reproduction curve based on the tri-color density curve derivation, change the recording setting of the high-light tri-color dots of the color separation image, and correct the high-order color cast accurately. If the original highlight three-color density is basically the same, only the dark tone of the three-color density is different, the density contrast is not equal, in the dark tones show a significant color cast. The tone level is slightly lost, and the high-level level is normal. You can change the color separation picture dark tone three-tone dot record settings, or add a color full tone background removal (only for mixed complex color role), to eliminate the tricolor record picture in the dark tone side of the color cast. It is also preferable to design a three-color hierarchical replication curve that adjusts the gray balance by deriving the three-color density curve, and correct the color cast with accurate data. If the original tri-color density curve is crossed, the image is high-profile biased to one color, and the dark tone side is biased to another color, which is the cross-color cast caused by the three-color balance of the photosensitive sheet itself. The levels of tone at all levels are not good. It is not easy to correct the color cast on the scanner or the color separation machine by changing the three-color level adjustment and recording settings. It is necessary to derive accurate adjustments based on the three-color density curve. Gray balance three-color level replication curve, guide its three-color level adjustment and record setting, can make its copying effect slightly improved. Differences in color cast density of 0.2 or more are generally difficult to correct. When faced with a more serious color cast, the color difference of the three color differences more color original, in addition to measuring its high light, dark tone density meal, it is best to add the middle of the original tone of the scenery should be neutral gray three-color Density, the color draft, needs to be based on the tri-color density curve, deducing the design to accurately adjust the gray balance of the three-color hierarchical replication curve in order to adjust the color cast on the desktop system and the color separation machine. However, when dealing with the color cast of the original, care must be taken to carefully analyze whether the image is really color cast, because some are artistic effects that the author intentionally created. For example, in backlighting photographs, due to the stress of backlighting works, the color tone changes greatly, and various color tone patterns can be formed. Some are based on warm colors, while others are based on cool colors. However, it must be taken into consideration that some shades of the backlight photographs look somewhat distorted. In fact, the author deliberately pursued it. Therefore, this type of manuscript cannot be considered as a color cast. Therefore, the manuscript should be carefully analyzed and fully reproduced during copying. Understand the author's creative intentions and accurately grasp the keynotes of the screen. The manuscript with obvious color cast not only requires very precise measurement of the three-color density data, but also needs to take into account the correction of color cast when color separation is performed. The tri-color version of the original copy must be used to balance the tristimulus of the original color tone. To be adjusted, redistribution adjustments must be made to their levels, which should be the focus of operations. The correction of the color reproduction error is based on the adjustment of the three-color version to the data of printing gray balance. Due to the change of the color shifter color signal, the color correction data will also change, which needs to be based on compensating the color shifter to eliminate the color shift after the color shift and chromatographic color combination data, and finally correct the color error.

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.

(to be continued)