Color Printing Quality and Prepress Technology Adequacy (I)

1. Picture separation

The key to color printing is prepress, and the key to prepress is color separation. In order to improve the printing quality of color newspapers, within the scope of the printing factory, it is necessary to first effectively control the important steps of color separation of the pictures so that they can adapt to the characteristics of newsprint printing as much as possible.

Classification of 1 manuscript

The manuscript is the basis for color separation and the basis for print reduction. The quality of the original document directly affects the quality of platemaking and printing. Due to the limitations of the process conditions, the printing of color newspapers is less effective than general color printing. In order to improve the printing effect of the newspapers and make up for this gap, it should have been more rigorous in selecting manuscripts with high definition, rich gradation, and vivid colors. However, it is still difficult to do this in practical work. First of all, the timeliness of the newspapers has determined that the choice between the content and the quality of the images is difficult. Most of them take the prominent content first. In the actual work, they even encounter clippings with poor results. This gives the picture The color separation brings great difficulty.

Secondly, the original manuscripts of the newspapers come from a variety of sources and are of various types. In addition to reflections, transmissions, and manuscripts, there are a large number of electronic manuscripts, including manuscripts, online downloads, and other digital manuscripts. The quality is difficult to control, and sometimes the original document itself has a low accuracy, a small amount of memory, a high magnification, and a loss of conversion, which seriously affects the effect of the image.

In addition, due to the requirements of the newspaper publishing process, the image processing process is limited to a short time range. Under normal circumstances, there is no time for proofing and color correction. Basically, one-off success must be achieved. According to the characteristics of the above newspaper production, the color separation operator of the color newspaper should establish a process specification for classifying the original based on accumulated experience and skillful operation techniques.

According to the type of manuscript, it can be divided into transmissive manuscripts, reflective manuscripts, secondary manuscripts, electronic manuscripts, and so on; according to the manuscripts, the content can be divided into conference scenes, indoor figures, outdoor figures, landscapes, artwork, etc.; according to the contrast of originals and Levels can be divided into high contrast, low contrast, and medium gray tone types.

According to the color separation characteristics of various types of manuscripts, the color separation rules, processing points, and controllable data range of various manuscripts are gradually explored and summarized. For color separation operators, this is the most basic and detailed work. It requires both the accumulation of work and repeated testing and verification. Only by establishing a specification for the quantification of different types of manuscripts can we strive to achieve a one-off success at a limited time.

2 scan settings

In order to adapt to the printing process characteristics of color newspapers, the setting of the scanning should focus on improving the clarity and gradation of the picture. In this regard, the following aspects should be noted.

a. Try to increase the scanning resolution value, select the correct number of screening lines, and scan with the resolution that can be divided by the resolution of the photon of the scanner. In particular, when the magnification of the picture is large, it needs to be multiplied by the magnification.

b. In order to reduce the level of loss, the range of gradation should be set to the maximum range during scanning, and the color tone should be pre-adjusted. According to the type of the picture, the black and white fields and the tone curve are pre-set.

C. In order to improve the clarity, sharpen the picture. According to the smoothness of the picture surface and the number of lines of the second manuscript, the sharpening value is appropriately adjusted.

d. The second manuscript is descreened.

e. In order to improve the timeliness, automatic adjustment function can be adopted and the scanning system can be used for automatic correction. When using this function, you should try to scan one picture at a time or sort them by tone type to avoid the automatic adjustment of the tone of different types of pictures.

In addition, the image and scanner must be kept clean during scanning to avoid dirt.

3 image processing

The color separation of color newspapers must be based on the characteristics of newsprint printing, adjust the image adaptively, and focus on the printing method to achieve the best results on newsprint.

In image processing, it is particularly important to point out that the effect of color on computer screens is very different from the actual printing effect of color newspapers. In the absence of automatic management of screen colors, data must be based on data to establish data. The specification of the operation.

Before processing the image, it is necessary to check the quality of the scanned image. The method of reading the brightness value of the highlight area and the darkest area can be used to check whether the scanned image has enough tone levels. If it does not reach the technical scope, it must be Rescan.

a, black and white field settings Black and white fields are the starting point and end point of the image tone. Correctly setting the black and white fields is an important part of understanding the tone. Since the whiteness and the ink density of newsprint are much lower than those of ordinary color prints, the tone of the printing of newspapers is compressed to a smaller extent. In order to improve the printing effect of the image, the black and white fields must be re-set according to the characteristics of the main body of the image, intentionally compressing the tone that does not affect the main image area, so as to play a role in increasing the contrast.

For general color prints, in order to achieve color reproduction, the level of the high-profile area is preserved, and the white field is usually set to a high-light area where the range is relatively small. In the printing of newsprint, the small outlets in the high light area are easy to lose. In the case of paper with more than 5% of grayscale, the excessive emphasis on the level of brightness adjustment will affect the overall tone range, making the picture dark.

Therefore, the whitefield area should be appropriately enlarged to increase the image brightness by 5-10, and sometimes it is necessary to sacrifice some bright-toned levels in order to highlight the main body. At the same time, it should be noted that the area of ​​the whitefield should not be too large to prevent a large area. network.

Whether the picture level is rich or not is reflected in the dark tone. For general color prints, the darkest smaller area is mostly selected as a black field in image processing. However, according to newsprint printing, the high expansion rate of outlets and the ease with which the outlets appear to be hierarchical, in order to take care of the overall effect of the image, it is also necessary to abandon some of the darker levels when necessary.

The purpose of re-setting the black and white fields of the image is to adapt to the characteristics of newsprint printing, to expand the tone of the subject as much as possible, and to increase the effect of contrast. The determination of the black and white fields requires tracking and detection of the printing effect, and on the basis of accumulated experience, the correct determination of the image subject is achieved.