Quality control of color reproduction of the hotte

Quality control of color image color reproduction

1 color printing image quality evaluation

quality evaluation is divided into subjective evaluation, objective evaluation and comprehensive evaluation

subjective evaluation refers to the evaluator's reference to the technical indicators specified in the standard, focusing on the factors related to quality, and drawing the evaluation conclusion through a comprehensive and systematic evaluation and comparison of the quality of printed samples or printed matter. The subjective evaluation is affected by the evaluator's own psychological impression in terms of knowledge, technical quality, aesthetic views and hobbies, and its results often vary from person to person, and it is unlikely to draw a unified conclusion. For example, the visual differences caused by different locations and surrounding environments, especially when the lighting conditions of the observed replica (compared with the original) are different. Subjective evaluation can not fully reflect the quality characteristics of printed matter, but it is the final arbiter of the project investment estimate of 4.94 billion yuan. At present, subjective evaluation is the main method to identify the printing quality, but the subjective evaluation factors should be objectively explained to make it scientific and consistent with the objective evaluation

the objective evaluation is centered on the determination of the physical properties of the printed matter. The physical properties of the printed matter are quantitatively tested by closing the oil delivery valve after the sample is broken through instruments or tools combined with the printing quality standard, and then the conclusion is drawn through mathematical statistics and necessary comprehensive analysis. Objective evaluation eliminates human interference and makes the evaluation results more scientific and consistent. However, objective evaluation requires higher implementation conditions. There are still some specific problems and difficulties in completely adopting objective evaluation methods to evaluate the quality of printed matter. At present, some printing enterprises have used this evaluation method throughout the process of process design and production to control the printing quality randomly and automatically. For example, electronic pre proofing during plate making, ◆ 5 Plate material detection device in the printing process of lignin plastic, remote control device for water supply and ink supply in the printing process, etc

comprehensive evaluation is a method based on objective evaluation, subjective evaluation and various factors. It is an effective method to evaluate the quality of printed matter at present. According to the provisions of the standard, it can objectively evaluate the quality of printed matter on the basis of using some test supplies (such as signal strips, test strips, control strips, ladders), combined with people's color psychology, physiology and other factors

there is no unified comprehensive evaluation standard at present. People are still constantly exploring and developing. Therefore, in the current work of evaluating the quality of printed matter, we should still take the technical indicators specified in the standard as the basis, and pay attention to the relationship between them. In the evaluation, we should focus on the technical indicators such as gradation value, color, dot, relative contrast and so on to comprehensively and truly evaluate the quality of printed matter

2 methods to control the color quality of printing image

in printing production, paper, ink and printing plate are all constraints on the quality of printing image. But when these factors have been determined, how to control the color quality of printed images when image reproduction production is carried out on the printing machine

1) adjust the printing pressure according to the specific production conditions

adjust the printing pressure according to the printing image reproduction quality requirements, paper thickness, printing plate and other conditions, so that the image points can be best reproduced

2) reasonably arrange the color sequence

at present, multi-color printing generally adopts black, cyan, magenta and yellow sequence or cyan, magenta, yellow and black sequence. This color sequence makes color reproduction easier and more accurate. The ink layer thickness is arranged from small to large. For example, when black, cyan, magenta and yellow sequences are used in offset printing, the ink layer thickness is: black ink is 0.8 μ m. Green ink is 0.9 μ m. Magenta ink is 1.0 μ m. Yellow ink is 1.1 μ m； The viscosity of ink is arranged from large to small, such as 1188pa for black ink, 488pa for green ink, 477pa for magenta ink and 147pa for yellow ink. When the ink viscosity cannot meet the arrangement requirements, the ink viscosity can be adjusted in advance

3) calibrate the printer

adjust the printer according to the printed sample and the established printing conditions to make the printing image effect consistent with the sample as much as possible

4) inking device temperature control

some printing machines can be equipped with or optionally equipped with inking device temperature control devices. In the process of inking, the ink channeling roller rotates and moves, so its temperature rises the most. During temperature control, it is generally to pass cooling water into the shaft core of the ink channeling roller to reduce the temperature, so that the surface temperature of the ink such as soft PVC roller remains stable, so as to ensure a stable ink supply. In addition to the ink channeling roller, some printing machines also put cooling water into the ink bucket roller to cool down

5) ink supply control

the field ink density on the surface of the printing image directly affects the reproduction color quality, and the field ink density is affected by the ink supply (the thickness of the ink layer on the surface of the printing image). As the ink layer thickness increases, the field density also increases. After reaching a certain point, the field density will not increase with the increase of ink layer thickness. The ink supply amount (ink layer thickness) can be adjusted according to the quality information of the printed image surface control strip

at present, the automatic adjustment of ink volume of printing machine mainly includes two parts, namely, the overall ink output of ink bucket roller and the adjustment of ink volume in each local area of ink roller. The overall ink volume adjustment ensures the correct reproduction of the order and tone of the whole picture of the printed image. Due to the different distribution of the printed image on the whole page, the demand for ink volume in each area is also different. Therefore, the ink bucket roller is divided into several small ink areas along the axis direction of the ink roller. The ink volume sent out by different ink areas is different to meet the different demand for ink volume in each local area of the image

6) water supply control

the water volume of offset printing plates must be controlled. The amount of water should vary with the printing speed and ink supply of the printing machine, so as to ensure the balance of water and ink, so that the printed image will not be blurred, the color saturation is good, and the plate will not be pasted

source: PRINT world author: Ren Lijuan, Cheng Ganghu