The best copy of the hottest tone level I

The best reproduction of gradation (level) (I)

section 2 the best reproduction of gradation (level)

due to the limitations of printing materials, technology and other factors, most color continuous tone original images cannot be faithfully copied and reproduced, but can only make the printed image as close to the original as possible. From the perspective of detecting image parameters and controlling image quality, it is very important to understand what is the best color and tone reproduction of the image, and the relationship between each reproduction process and printing process and this best reproduction, because there are many causal relationships between pre and post printing processes

I. The importance and complexity of controlling image gradients

1. The importance of controlling image gradients. Hierarchical reproduction is a term to express the state of image reproduction. The former is a relatively general term, and the latter is a more specialized term after the emergence of electronic color separators. Tone reproduction generally refers to the correspondence between a group of copied tone values and the corresponding group of tone values on the original. The tone values can be expressed by density values or point coverage values. Hierarchy is defined as the visually distinguishable density level in the image

when the tone of an original is best reproduced, the image will show satisfactory contrast, the important details on the original will be displayed, and it will help to achieve balance in the whole picture. If it is a low contrast original, you can locally correct the tone during copying, so as to obtain a more satisfactory contrast

when the gradient copy is incorrect, the printed image looks not made of new materials, and the joint will begin to expand brightly, lacking the due natural luster, brightness adjustment or contrast. Important parts give people a "flat" feeling, and the color saturation is not enough. Sometimes, poor tone reproduction may be related to some seemingly unrelated problems. For example, improper tone reproduction may make some parts of the replica lack saturation, and even make some colors appear large color difference. People may think that this is caused by improper color correction and adjustment of electronic color separation. In fact, it is not caused by color correction, but by improper tone reproduction, and may also affect the three color gray balance. This deviation cannot be corrected by color calibration control, and the range of color calibration required by it has exceeded the capacity of the equipment

2. The complexity of tone reproduction. Tone reproduction is the most important parameter for the final effect of printing reproduction, but the best tone reproduction is relative because: ① in the production process, tone reproduction is often subjectively decided by the operator according to some criteria. ② For a given manuscript, the actual effect of tone adjustment cannot be accurately understood before the sample or print is printed

the best tone reproduction is not only related to the production of color separations, but also related to some other technological factors. Among them, it is mainly the quality of ink and paper, the shape of dots, the number of lines added, the density of field ink on paper, and relevant printing characteristic parameters such as dot increase, dot directional increase, overprint and paste, which participate in the management of strong hydraulic oil. We should organize standardized production, quantify the impact of these process factors on the tone reproduction, and compensate in the stage of making color separation chips

3. different gradient reproduction curves and their image effects. Tone reproduction curve is a method to express the relationship between the density of originals and printed copies with curves that can be widely used in many fields such as new energy vehicles, aerospace and so on. It is a useful tool to demonstrate the effect of tone reproduction

in the process of color separation and printing reproduction of a given original, its hierarchical reproduction can be artificially changed, and the adjustment value of the original can be expanded, compressed or kept unchanged

Figure 3-1 is a curve showing the relationship between the original density and the printed copy density. If the density range of the original is set to 1.00, curve a indicates that the density range of the replica is expanded, and the density of the copied is about twice that of the original. The curve is steep and the slope increases. Curve B represents the reproduction of compressed tone. The contrast of the copied is smaller than that of the original, about half of that of the original. Curve C indicates that the density of the copied copy is the same as that of the original, which is a 45 ° straight line. At this time, it can be considered as a good linear copy

under the condition that the density range to be copied is fixed, people can get different shape tone reproduction curves by changing the ratio of each tone area between the original and the copy, so as to get different tone reproduction effects. Figure 3-2 lists several tone reproduction curves of different shapes: curve A is an elongated "s" shaped curve, which is copied "flat" in the dark and bright areas. In these areas, details will be lost, making the bright tone of the printed copy pale and the dark tone dark. Lack of details, the size is longer and wider than 50cm than the base of the hydraulic universal material testing machine, and the whole image becomes hard, but the middle part of the curve is copied in a larger density range, and the expressiveness of details increases; Curve B is a soft copy curve, which increases the details of bright and dark tones, but reduces the details of intermediate tones; Curve C and curve D are two extreme examples. Curve C expresses a kind of light tone reproduction, and the contrast and detail of the dark tone area are increased, but the light and intermediate tones are copied flat and the details will be lost; Curve D, on the contrary, is a dark copy curve, the whole tone darkens, there is an obvious rise in the bright tone area, and the dark tone end is flat; Curve e is a skeleton black tone curve applied to the black version. There is no bright tone level at all, and there are few middle tones, but there is a high dark tone contrast

source: must win