The main tool for testing the field density of output film is densitometer, which is used to test whether the output density of output color separator 100% dot meets the printing requirements. When the output field density meets the printing requirements, if the field output density of newspaper printing is greater than or equal to 3.5, there is no need to adjust it. Because the output density and development conditions of the laser imagesetter are unchanged, it is only necessary to test one color plate when testing the field density of the output film, and it is not necessary to test four color plates for color separation at the same time.
Second, the significance of measuring film field strength:
Our country has formulated corresponding standards for various printing methods and the field density of films output by printing materials. Therefore, it is necessary to treat the field density of the output film differently according to different printing materials and printing methods.
For example, in the printing of most newspapers at present, the third part of GB/T 17934.3—2003 national standard "Cold-set Ink Offset Printing for Newsprint" is used, which stipulates that the field density value of color separator must be greater than or equal to 3.5; For other printed matter, the field density value should not be lower than 4.0, and some high-grade printed matter should be higher than 4.0.
At present, many printing enterprises, especially small and medium-sized printing enterprises, don't have professional film field density testing ability, and film field density testing (without purchasing densitometer) is mostly done by magnifying glass or visual inspection by experience; In addition, different brands of developer and fixer have different effects on the output film field density, and the development temperature in different seasons and different brands of laser imagesetter have different effects on the film field density. This will lead to the unstable field strength in the actual output process, which can not meet the requirements of the national standard.