Third, compensation for network expansion and losses In pre-press processing, we must ensure that the impact of each step of work on multiple points is stable and predictable. If this is not done, the next step will be an error, and it will be even more severe. It is not possible to macroscopically control the exact copying of images in subsequent processes. In the process of plate making and printing, it is very difficult to maintain the accurate residence of the image. Once unpredictable dot changes occur in one step, the probability of obtaining a successful silk screen product is very small.
For ease of discussion, this article starts with the monitor and discusses how to compensate for network expansion and loss. First, make sure that no direct light is projected onto the monitor screen. The best working conditions are in soft daylight. A strong light source in the surrounding environment can cause the monitor to display images incorrectly. Second, to ensure that the monitor's white is pure white, R, G, B values ​​are 255; display black is pure black, R, G, B values ​​are 0.
1. Test Monitor There are two methods to test the monitor. Method one: Make a gray ladder rule in PHOTOSHOP, the beginning is pure white (0%), and then gradually becomes pure black (100%). On the display screen, move the mouse to the part of the original image where the hue changed. Then use the INFO PALLET in PHOTOSHOP to get the value of this part. The white area of ​​the image should be very close to the white end of the ladder, if not, The monitor needs to be recalibrated. Method 2: Select an image to test its pure white and pure black parts. If pure white values ​​are not 255, 255, and 255, pure black values ​​are not 0, 0, and 0, and your monitor needs to be calibrated.
2. Adjust the imagesetter The imagesetter is the second device to pay attention to. This step requires a simple image tone test with ADOBE ILLUSTRATOR, MACROMEDIA FREEHAND, or CORELDRAW, which is a grey scale test with a percentage increase in dot. The starting position of the grey ladder rule is 0%, 1%, 2%, 3%, 4%, 5%, starting from 5%, increasing by 5% of the difference to 95%, and then increasing by 1%. To 100% of the field. Send this test strip to the imagesetter and measure the output film with a transmission densitometer. First, measure the real-time area of ​​the film and check that DMAX meets the "4.0" requirement. After measuring the percentage of dots on each stage of the film, if the percentage of dots is closer to the expected value, the deviation is between 1% and -2%. At this time, the CURVE curve of the gray scale EPS file sent to the imagesetter can be adjusted. The CURVE curve is a means that users often use to adjust the hue of an image.
If your company has its own image-setter, you can set the CURVE curve directly to the RIP so that each time the film is exported, it will be convenient.
If the percentage of dots on the output film increases by more than 2% from the expected value, it is necessary to adjust against the rower. For an ordinary phototypesetter, it is generally to adjust the exposure time or adjust the degree of development of the film, and sometimes to adjust these two aspects. The factors that affect the exposure time are listed below:
(1) The laser voltage is high or low;
(2) Laser or laser diode aging;
(3) There is dust on the imaging lens;
(4) The developer needs to be replenished with developer;
(5) Incorrect developer concentration;
(6) The developer has been used for too long and has lost its development effect;
(7) The temperature of the developer is high or low;
(8) Development time is too long or too short;
(9) Some films are incompatible with developer formulations.
If the imaging device used is not an ordinary imagesetter, but a laser printer or a thermal imaging imagesetter, the basic principles described in this paper still apply.
Although there is a slight difference in each imaging setup, the imaging on the film surface must be precisely controlled, the opacity of the image area must be high (DMAX), and the halftone must accurately reproduce the image file. It is also necessary to use a transmission densitometer to check if the film density value meets the requirements.
Many prepress companies typically perform phototext test and computer monitor tests to ensure that film is available. When they test, they usually use a test strip file, add 200 LPI to it, and after outputting the film, measure the minimum and maximum percentages of the dot at 0.5%, 1%, and 1.5% of the high-profile part; 98.5 for the shadow part. The minimum and maximum values ​​were measured at %, 99%, and 99.5%, and then compared with the expected values ​​to determine the expansion and loss of the network. Whenever testing, it should follow such a principle: test resolution at least equal to two resolution print. For example, if the resolution of the output film is 65 LPI, then the resolution of the linearization test is 133 LPI, so that a better height result can be obtained and a better print can be obtained.
IV. Concluding remarks The common mistake made by screen printers is to assume that the outlets of the output film are accurate. However, no matter how advanced the image-setter you use, calibration and periodic tests are essential. As long as we effectively correct the dot changes in pre-press processing, then we can completely Changes to macro-control.