In the process of commercial transactions, it is especially important to make appropriate quality evaluation of printed matter. The complexity of color printing process is well known. The production of a printed matter often takes more than a dozen steps to complete, including companies, staff, etc., different environments. At different times, the evaluation methods or requirements for printed materials are also different. Therefore, in this process, some specifications and corresponding observation conditions need to be set.
Therefore, we can only subject the external factors such as the environment to subjective evaluation of printed materials. This is fair and objective, so as to reduce the disputes caused by the environment, so the standard lighting environment and standard light source are necessary. .
Color difference of printed matter
The color difference can be divided into (1) original color difference: the color tone of the reproduced original is the purpose of printing and copying, so that the degree to which the printed matter and the original are difficult to distinguish is the highest standard of subjective evaluation. (2) The same batch of color difference: refers to the same position of the same batch of products in the same hue area, the color error between different sheets. (3) Color difference between different batches: refers to the color error between different batches of the same product. If the colors of each batch are slightly different, when they are put together, the customers will feel that these goods have new and old points, and even suspect Whether its intrinsic quality will be as unstable as the appearance will cause distrust of the goods, and naturally cause manufacturers to be dissatisfied with the quality of the printing products.
As customers and printers, it is hoped that the value of this color error is preferably zero. However, due to various conditions in actual production, it is impossible to completely eliminate the color error. It can only be achieved by strengthening the quality control of each link. The color quality difference is controlled within the specified color difference standard. Color tolerance refers to the color difference between the printed matter and the original or proof sheet that the customer can accept.
Subjective evaluation
The subjective evaluation of the color quality of printed matter is based on visual inspection. After observing the printed matter and comparing it with the manuscript or the printed manuscript, the observer makes his own judgment. The main consideration is how much the color quality of the printed matter will be accepted by the customer.
Whether in the printing process or in checking the quality after printing, the printing operator or quality inspector should always evaluate the color quality of the printed product based on his own feelings and experience, based on the faithfulness and authenticity of the reproduction.
The faithfulness of reproduction refers to the extent to which the print reproduces the color tone of the original. Print is a kind of reproduction. From the prepress processing to the whole color reproduction process of printing, the original is the basis of our work. The color tone of the original is the purpose of printing and copying. The degree to which prints and manuscripts are difficult to distinguish between true and false is the highest standard of subjective evaluation.
When there is no original for comparison, the color quality of the printed matter is related to the sense of reality, that is, it is required to conform to the memory color of most people. The average person has a preconceived habit of common objects. If the color of the subject in the printed matter is different from the color of the real object, the printed matter cannot be called a high-quality replica. In short, the subjective evaluation criteria for the color quality of printed matter is to copy the true, natural, and coordinated, and of course, sometimes with the customer's intention or the use of the product.
Original definition
In the past, most of the manuscripts came from photographic slides, photographs, and hand-painted manuscripts. In the process of color separation, if you can access the original, it is considered a valid color reproduction. In terms of printing, the drafts approved by the guests are used as guidelines, and as long as they can follow 90%, they are generally considered qualified.
However, there are more definitions of computer-original manuscripts today. For example, if a guest sees a satisfactory color on a computer screen or a printed manuscript, they think that this is an original. Regardless of the type of original, the colors they record or appear may not be acceptable under normal printing conditions, as each color reproduction system has its gamut limitations. In the production process, the image ingestor is the original, the color separation plater takes the photo taken as the original, and the printer uses the manuscript as the target of color matching.
objective comment
The objective evaluation of the color quality of printed matter is to calculate the result of subjective evaluation by statistical means, and then convert it into the corresponding physical quantity, and use it as an objective evaluation standard. This can eliminate the influence of human factors in the evaluation, and evaluate the color quality of various printed materials fairly by the standardized unified standard, and finally make it more in line with the subjective evaluation criteria of the majority. The objective evaluation method mainly uses specific measuring instruments and tools, and measures some standard elements printed together with the printed image. Only by measurement can the printing quality be controlled to some extent.
Color quality and production control
In order to produce high-quality color prints, it is necessary to strengthen the quality control of the production process, and quality control mainly depends on the objective evaluation criteria of the product, that is, to develop a strict data specification, and objectively measure and use various instruments. Evaluate the color quality and other qualities of the printed matter.
The purpose of color control management is to improve the small gap between originals, proofs, and products. In the printing process, if the printed matter can be spot-checked at any time, the problem can be found through the biased data, and the cause can be found in time to correct the problem, thereby ensuring the copy quality of the printed matter. In addition to using density as a parameter to reflect the color quality of printed matter, it is necessary to promote the color CIELab chromaticity value as a parameter for detecting the quality of the printed product.
Every link must be managed in a data-based manner. Every step must have a testing tool to detect it, otherwise there will be many errors. Nowadays, with the continuous advancement of process technology, the color control methods in printing have been further developed. The new color management system makes printing color control convenient and more effective.