The Trend of FM Screening (II)

V. Dot gain and tone compensation for FM screening

In print engineering, it is almost impossible to avoid dot gains. The dot gain phenomenon is divided into two types: physical dot gain and optical dot gain. Regardless of whether or not the species is present at the junction of the graph and non-graphic components. The amount of its occurrence will be the sum of the surrounding long (thick line in Fig. 4), and the printing environment will differ depending on the type of printing machine and the arrangement of the rollers (see Fig. 4).

As such outlets increase, AM outlets and FM outlets are very different. What often becomes a problem is the increase in physical outlets. Because the total length of the FM screening network must be long, if you do not compensate for the printing, there is no doubt that the FM screening party will have a darker tone than the AM screening. In order to minimize the difference between these tones and to obtain natural results as much as possible, at the time of FM screening, the tone was compensated for when the image was output from the CTP to the printing plate. In the case of Staccato, the difference between the reproducibility of AM screening and FM screening is firstly calculated, and the compensation curve is plotted. Then, the four colors of YMCK are handled by a compensation curve, and it is easy to coordinate the hue. .

VI. Colourfulness of FM screening

It is generally believed that the color of FM-screened prints is always bright. This is caused by the effect of optical dot gain. Shang-Tzu mentioned that dot gains occur at the junction of the map and non-graphic parts. As with physical dot gains, optical dot gains also occur at the junction. The physical dot gain is actually a phenomenon in which the ink image (ink film) is crushed and becomes large due to the press pressure, and the optical dot enlargement seems to reflect the phenomenon in the human eye.

On the AM screen print, the printed image was cloudy compared to the actual document. This is not the turbidity of the ink itself, but the turbidity felt by the moment the white paper around the ink image is reflected in the human eye. It can be seen from Figure 6 that when dot gains occur, FM screening increases the amount of dot gain compared to AM screening. Therefore, it is difficult for the naked eye to feel white on the paper, thereby reducing the color turbidity. . According to this phenomenon, the color of the ink image looks bright.

In addition, Staccato occasionally worked on various colors of the dots to reduce the overlap, thereby reducing the color turbidity caused by the reflected light from the paper white and the overlap of the ink. At the same time, the ink film was thin and the midtones were increased. Color saturation plays a role.

VII. FM screening and consumption reduction

It does not have a screen for AM screening. One of the biggest features of FM screening is the reduction in ink consumption. As mentioned earlier, AM screens are different in the size of the dots. The ink is in a viscous flow. The thickness (ink volume) of the ink film is different in the positions of large dots and small dots. Therefore, the amount of ink applied is not uniform, and the ink supply amount has to be adjusted during the printing process (toggle to the ink key). On the other hand, FM screening is due to its finest ideas. There is a certain limit to the amount of ink applied. The ink film is also thin and uniform. It can be printed by supplying a minimum amount of ink, thus saving the ink consumption.

According to the printing test of Creo's official printing press, 18-34% of ink-saving reports have been reported. Considering that the dot gains are increased, the FM screen and the AM screen are used to obtain the same reproduction. Comparing the image area (inking area) on the compensated plate, an area difference of 10% occurs. In fact, the ink consumption measured by the printing company's web offset press also resulted in an average saving of 15-17%.

Regardless of how the printing aspect is concerned, from the perspective of saving ink consumption, it also shows a non-negligible effect. However, this is in terms of photographs and equal density and other tonal images. If it is text or print only on the ground, then FM and AM screening are exactly the same. Moreover, even if there are tonal images, there will be differences in the reduction effect due to the depth of the tone.

8. Concluding remarks

In the current printing industry that does not expect large technological innovations, as a strategy for differentiated printing products, with the popularization and popularization of CTP, it is absolutely true to reassess the effectiveness of FM screening. However, it is still at an early stage and there are still many issues to be solved.

The current prepress works and printing workflows are mainly based on the process of AM screening. Among them, the addition of screening to FM screening will bring many problems to be solved in color reproduction and other aspects. When solving these problems, FM screening becomes a complete workflow. This is not only to improve FM screening software, but more importantly to improve ink, paper, plate, dampening syrup, blanket, and printing. All aspects of the machine, in the face of these problems that need to be resolved, are expected to be coordinated by the relevant manufacturers.