Formation of printing dots in printing manuscripts and its production mechanism IV

3, tone level
The reproduction of the tone level of the print image depends on the quality of the copy of the dot. If the edges of the outlets are incomplete, the expressiveness of outlet percentages cannot be completed. If the outlets are not imprinted, they will not be able to absorb enough light and the dark tone will not be black; the outlets will be expanded, the dark tone will be increased, the midtones will be reduced, and the printed products will appear dark.” "Boring"; outlets shrink, lighting increases, dark tone, printed products appear to be "flat floating"; ignore the middle tone, highlighting the bright tone and dark tone, although the printing of "Yao" but "empty"; prominent middle tone, ignore the bright tone and Dark tone, printed products "light and light."

The ideal image reproduction requires that the density of the original and the printed matter satisfy a 1:1 correspondence. As shown in Figure 13(a).

Figure 13(a)
In reality, this kind of ideal level replication curve is impossible to achieve, and sometimes it is not necessary. Because (1) the print is a visual effect product, to meet people's subjective requirements, as shown in Figure 14 through the reinforcement of the details of the antique enhance the artistic appreciation of the print; (2) from the original to the print The efficiency of each image transfer process can be limited by various subjective and objective conditions, such as the color sensitivity of the film, plate quality, exposure conditions, development effects, printing pressure, ink characteristics, and paper properties. Therefore, the manuscript density range is generally greater than the density range of the print replica, such as the manuscript density is generally 0.05 to 3.0 (even 4.0), the density contrast up to 2.95 and greater, and the current print maximum density range is 0.00 - 1.8, the density contrast is 1.80 as shown in Figure 13(b). Based on this, in the process of printing and copying, the level of the manuscript must be compressed to suit the requirements of the printed matter.

Figure 13(b)

The problem is that the compression of the tone levels will inevitably cause levels of parallelism, loss, and poor image quality. Therefore, in actual work, depending on the original type, customer requirements, and copying process, flexible adjustment of the level curve, emphasizing the main part, loss of minor parts, highlighting the theme, and ensuring the overall copying effect of the image.

Figure 14

As shown in Fig. 15(a), a high-light-adjusted gradation curve is selected. With curve A, the levels above the density “a” on the manuscript are all reflected; with the curve C, the levels above the density “c” on the manuscript are all reflected, but the levels below the density “c” disappear into bright Tone. Comparing the three curves, the area of ​​the high-light area C>B>A; the degree of darkness of the image A>B>C; the richness of the light-toned layer A>B>C.

Figure 15(a)

As shown in Fig. 15(b), the tone adjustment curve is selected as the level curve. With the curve A, the levels above the density "a" on the manuscript are all merged into the ground, and with the curve C, the levels below the density "c" on the manuscript are reproduced. Comparing the three curves, the area of ​​the solid area A>B>C; the degree of darkness of the image A>B>C; the richness of the shadow level C>B>A.

Figure 15(b)

As shown in Fig. 15(c), the mid-tone adjustment hierarchy curve is selected. The overall image density value A>B>C; dark tone level richness A>B>C; light tone level richness C>B>A.

Figure 15(c)

(to be continued)