The basic elements of color standard and analysis (1)

Application Term Field Density In the process of printing process control and image replication control, field density is the most important characteristic that needs to be measured. It represents the maximum solid color saturation that can be obtained during the reproduction of the print. However, since the density of the solid in any particular printing process is related to the thickness of the ink layer, this characteristic also controls the copying process. The rest of the section includes non-field areas. In addition to controlling the saturation levels of the main tones and the overprinted solids and shades, the balance between the main tonal density determines the overprinted hue. (For example, the density of solid yellow and solid blue determines and controls the generated green hue). Other printing properties, such as dot gain, print contrast, and chromatic aberration, rely on the density of the ground to determine whether they represent normal or abnormal printing conditions. For example, when the density value is greater than or equal to the value on the color scale, it is also controllable if a larger dot gain is normal; conversely, if the dot gain is higher than the normal value when printed at a density lower than the requirement, It shows that there is an abnormal situation. At this time, even if the image seems acceptable, it still needs to take action to solve the problem. Other independent printing variables, such as Plate exposure, package level, and tumbler settings, also play an important role in image hue and color control. The field density is the only variable that the print operator can adjust during the press run. Print contrast The print contrast is a measure of the density of a field in a printed product compared to the density at a 75% tone of a certain color. It is a very useful printing property because: It is marked on the tone curve. The copy status of the image. Although print buyers are unaware that they are visually evaluating print contrast, they actually use this property as an evaluation of print quality. Prints with high contrast usually give people a feeling of jumping, which is mainly due to the three-dimensional nature of the darker regions with higher saturation and the comparatively stretched three-quarter-tone regions, as if they are to protrude from the paper. · The print contrast data itself provides a wealth of process information, including, 1) ink density, 2) dot gain values ​​in the more important three-quarter tone areas, and 3) having no reproduction of quarter-tone areas When the dots are enlarged, the ink density can be increased. The larger print contrast value indicates that the density of the solid ink increases and the density of the corresponding three-quarter tone block does not increase. (The increase in three-quarter tone density may be due to dot gains, stencils, dirt, or other factors) so that the visual contrast between the field and the three-quarter tone zone increases. The decrease in printing contrast shows: 1) As the density of the ink in the field increases, three-quarters of the hue area gradually fills up, making the image level smoother and reducing the contrast between the dark tone and three quarters of the area. 2) The print operator intentionally reduces the density of the ink in the field to spread out the important three quarters of the gradation, while at the same time flattening the image duplication, reducing the darkness and the contrast of three quarters of the area. Gray balance Gray balance refers to the halftone dot combination of cyan, magenta, and yellow, forming a neutral grey tone for a particular printer, paper, and ink combination. It is important to understand the grey balance of the printer-paper-ink combination, which prompts color separation and printing personnel to pay attention to the color correction during color separation. Gray balance color scales are particularly important for printer operators and administrators, as these three colors produce reddish, bluish, or yellowish colors or are somewhat heavier or lighter than inks with the same visual color density value. At the time, if the gray balance color patches are somewhat offensive, such as reddish, blue, or yellow, measurements can be made to trace the root cause of this unfavorable change. Although the gray balance is different for each printing press and varies for each roll of paper and batch of ink produced, investigations and experience show that the values ​​summarized in the entire market are still available. In Table 1 the proportions of each color ink that are available in the market to reach the gray balance are listed. Table 1 Visual gray balance percentage 25% 50% 75% Cyan 25% 50% 75% Magenta 16% 39% 63% Yellow 16% 39% 63% The gray balance in the table is the recommended value, not the standard Or specification. Also note that each color separation person will use different data. Although in theory one might think that the amount of the three inks used should be the same when replicating neutral grays, it is not. In fact, printing primary pigments is not as pure as it is theoretically, and it will reflect back some light that should have been transmitted. . Simply explaining the theory and the real world is necessary and useful: Theoretically, suppose that 1) the printed matter should be detected under white light composed of red, blue and green light with equal energy; 2) the paper is ideal white. The ideal cyan ink absorbs all the red light and transmits all the blue and green light. The ideal color ink can absorb all the green light and transmit all the blue and red light. The ideal yellow ink can absorb all the blue light and transmit. All the green and red light. The ideal paper is capable of reflecting 100% of the colored light reflected through the ink. In fact, papers and pigments with these desirable characteristics do not really exist. Because the mixture of pigments is not pure, the ink we use is like a contaminated pigment. Specifically, the cyan ink is like some color ink and a little bit of cyan ink. The yellow ink seems to be mixed with some colors. Ink and a slight amount of cyan ink. The fact that each color of the three-color ink is contaminated with the other two colors is also a factor that causes ink-ink balance color cast. As a result, color separation personnel must adjust the dot size to produce neutral ash when overprinted, and all three inks print the same dot size resulting in a brownish color. Also, because the ideal paper does not exist, the paper itself Become a filter, the light through the transparent ink can not be reflected back 100%. Apparent dot area and apparent dot enlargement Apparent dot area refers to the value of the printed halftone dot. For example, if we print 50% of the intermediate tone into 72% tone, we can say that the apparent dot area of ​​the printed film color mark is 72%. The apparent dot area value is a ratio of the hue value of a certain hue to the hue value of the solid. The enlargement of apparent outlets, also known as the expansion of total apparent outlets, refers to the noticeable enlargement of the hue (or the increase in the total value). For the above example, 50% of the apparent outlets expanded to 22%. Dot enlargement: • It is not a printing defect. Its occurrence is normal and predictable. It does not affect the printing quality as long as the following conditions are met: 1) Predictability and correctability of halftone dots in the process of color separation 2) Measurement and control during film making, proofing and printing. · Divided into two parts: The mechanical dot enlargement refers to the physical increase of each halftone dot area; and the optical dot gain refers to the human eye (under normal observation distance and typical observation conditions) or the densitometer The appearance of the half tone dot appearance. Several studies by GCA and other organizations have shown that mechanical dot enlargement is affected by many factors, including film copying, plate making, printing and packaging, paper surface properties, and ink properties. Each of these printing processes may change the upper half of the final print. The dot size and shape. The choice of positive or negative printing plates also has an effect. The way these plates are exposed increases the actual size of the midtones of negatives by approximately 2%, while the positive tone of the negatives increases by approximately 2%. On the other hand, optical dot enlargement is most affected by the type of paper. The optical absorption, hygroscopicity, and smoothness of the paper are the dominant factors affecting the human eye (or densitometer) to observe the halftone dot of the print. Absorption of ink by paper results in a large mechanical dot size, and the absorption of light by the paper results in an increased mechanical dot size. Absorption of light by paper results in an increased optical dot size. The degree of smoothness of the paper will affect the apparent dot gain, because the rough paper is not flat after it is magnified compared to the coated paper. And there is also a difference between coated papers. High quality NO.1 coated paper is smoother than NO.5 coated wood pulp paper. As the light hits the surface of the printed paper, hits individual fibers and coated particles, and scatters on the surface of the paper, the degree of smoothness of the paper surface affects the optical dot enlargement. The rougher the paper, the stronger the scattering. In the process of light reflection, due to halftone dots, some of them are absorbed by the ink. As a result, the dots are darker, as if the halftone dots are enlarged. When discussing the dot expansion: Consider the total apparent dot expansion including mechanical and optical components. When a customer examines prints or proofs, what is observed is the total apparent dot gain. Mechanical and optical factors have little effect on the total number at this point, but they are particularly important to the operator. Although mechanical dot enlargement can be estimated by observing the color scale, there is actually no accurate way to distinguish between optical and mechanical dot gain; this is viewed through subjective color elements. • Although dot gain can be calculated for different colorimetric values, total apparent dot gain usually refers to 50% midtone dot gain values, such as in Specifics for Web Offset Publications (SWOP). This is the case in the proofs. Blur/Double Shadow Blur/Double Shadow is a common printing problem that is caused by slight movement or secondary contact between the roller and the paper, more precisely: The double image is the image on the blanket transferred to the surface of the paper The secondary image that was generated when the minor registration was poor. Sometimes, as in the case of a skin cloth, only a part of the image is transferred to the paper, and the remaining part is inaccurately printed on the paper, and a double image is produced. At this time, the double image produces an extra-undirected image. Poor paper advancement and stretching of the rubber part, sometimes the paper tapping on the rubber part, caused the paper to come into contact with the cloth twice. This is the main reason for the double image. When a halftone dot occurs ghosting, each dot will have a slight shadow, increasing the mechanical (and optical) appearance of the dot. Blur is caused by slight sliding of paper or blanket, which causes the image to produce blurred images in the printing process. The phenomenon of insufficiency of the blanket will produce this phenomenon. After inspection, the blur will produce additional images with orientation, that is, the dots will only go in one direction. elongation. Blurring makes the halftone dots elliptical and changes in only one direction. It also increases the size of mechanical and optical dots. It also produces dot gains when double shadowing and blurring do not occur. However, both blurry and double shadows are general appearances. The cause of network expansion.