The Linearization Method Used to Control the Expanding and Loss of Dots before Screen Printing (top)

In all printing methods, there are dot-difference phenomena, and each printing method and every actual printing process has its unique dot-diffusion characteristics.
In screen printing, it is especially important to control and adjust the prepress work in order to compensate for the unavoidable dot gain in printing. This article will focus on the technique of obtaining the expected dot size on the substrate using the linearization method in digital prepress processing.
For each dot enlargement, the amount of dot compensation in prepress processing depends on how well the image in each step of the screen is maintained, but also how stable the dot is in repeated printing. Without these two aspects of control, it is impossible to make meaningful adjustments to prepress processing that directly affects the printing process.
First, the linearization of the related concept of linearization is from the beginning to the end of the printing process, the dot expansion and loss in each step of the workflow is linear and predictable. The linearization work includes: firstly, identify the change of outlets in each step of the work; second, make adjustments to the changes in the outlets so as to ensure that the image outlets to be copied are in a linearly changing process flow. Linearization means that the fidelity and accuracy of the digital information to be copied must be known in the prepress process. Of course, in every step of the work before printing, there will be dot gains or losses, but this kind of dot change is coherent and predictable. Therefore, digital files can be adjusted and controlled according to the dot changes that are expected to occur in the printing process of the plate making, thus achieving the purpose of compensating for the loss of the dot expansion.
Linearization is the basic method for obtaining good halftone color reproductions. However, it is a challenging process to set up the prepress system to be in the best condition to obtain a very uniform and consistent print, because the adjustment between its various steps will affect the next step; in turn, it It also affects the work ahead.
There are two principles to follow for linearization: First, you cannot take it for granted that the information on the screen and on the screen is accurate. Second, each step must be tested using a suitable method (such as using a density meter).
No matter how expensive the artwork set used, it must be tested and calibrated. Once detected and calibrated, the daily output works close to the optimal setting. This is the work that must be done in prepress work. Even if the print film is from a prepress service company or other supplier, the film should be inspected to ensure that the film can be used normally.
Second, linear detection work In order to grasp the halftone dot changes, at least two detection instruments. The first instrument is a transmission densitometer. This type of densitometer can measure the amount of transmitted light through a negative or positive film. Its mode of operation is generally set to the "percentage of dots," and the resulting reading is the percentage of the actual halftone dots. It is also possible to use a transmission densitometer to measure the DMAX in the field (maximum density) and the DMAX of the film's graphic area. Check the readings to see if the film is dark enough to prevent light from passing through the film when the screen is exposed. The reading given by the instrument is a common value for the amount of transmitted light. A reading of 4.0 means that 1/10000 of the flux projected onto the black solid film penetrates the film. If the reading is lower than 3.0 film, there is a danger of light leakage when the screen is exposed. The negative effect is that the halftone dot size and color tone will be changed.
The second instrument is a reflection densitometer. It is used to measure the amount of reflected light on the printed image surface. It can also directly measure the dot percentage, calculate the absolute value of dot gain, and the maximum density of the ink on the print. The reflection densitometer can directly give the inverted density of the Y, M, C, and K inks after the filter is installed, which can be used to control the percentage of dots and how the density of the ink affects the color tone.
We know that from white to black, each halftone dot also represents a hue. In other words, a 50% black dot represents a visual gray. Such problems often occur during the printing process. Therefore, it is necessary to detect every step in the printing process.
Typically, the inspection is pushed forward from the final printing process. Testing allows us to be aware of the issues that arise in each step of our work. The place where the dot change frequently occurs in the detection is given below, which is in terms of the characteristics of a typical screen printing image, and thus has the versatility.
1. Loss of dots in the printing process occurred in highlights and 25% of the surrounding area; dot gains appeared in midtones, 75%, and dark tone areas.
2. Loss of screen points in the process of plate making generally occurs in highlights, and the loss in the remaining parts is small. The dot loss in the highlights is due to the dots being masked by the screen and the light passing through the dots during the exposure.
3, the output film usually has little change in most areas of the network, but there will be a loss of dots in the high-light areas, dot-extension in dark areas.
4. Some of the images presented on the computer screen may appear to have dot gain or loss. This is because the GAMMA value of the screen, the calibration of the white and black fields, the color temperature of the monitor, and the light source of the environment will have an effect on the screen display. influences.
5, digital files Manuscripts in the digital file expansion and loss, often depends on how to make up the computer display results and adjust the image. (To be continued)