Prepress scanning separation operation for printing high quality images

The key to success in shadow duplication is the correct black edition setting

a. The black site selection should try to choose the neutral black part of the black object to ensure the accuracy of the black version of the network value setting; b. The black version of the network value setting: the offset process should be 65% to 85% (offset Paper is printed at 65% to 70% and coated paper is printed at 75% to 85%. c. Effective use of the black plate is not only to add a black plate to the three primary colors, but to reduce the amount of ink for the three primary colors in the black portion, so that Increase the uniform black version, use the black version to open the tone level, and increase the contrast of the original. General removal of 20%, remove the color plate network value is C78%, M68%, Y68%, K90%. d. The starting point of the black version is extended to 35% to 40% of the C version. Small dots can be added to the image, and the depth and depth of the image can be increased. Of course, the black version will be extended and the color part will be deepened. Make the necessary lightening.

Handle white and black in color pictures

The white and black colors in the color picture are not only the important colors in the picture, but also have a black and white tone, which makes the color appear pure and pure. No matter how bright "white" is, or how dark the "black" is, it has a certain color tendency, but on the concrete picture, there may be exaggerated white and exaggerated black. Therefore, we must pay attention to the black-and-white tone processing in color images when we copy.

Various white objects in color photography pictures, such as: white clouds, white flowers, white porcelain, etc., have different texture characteristics and should be different when setting adjustments. Brightness should be 2% to 3% of the C version, M, Y version is not a net, usually 1% to 2%.

Many white objects of current prints often exhibit color casts and delusts due to the lack of awareness of gray balance among some operators. For high-gloss white objects that require a level, set the gray balance point value ratio, such as C5%~6%, M3%~4%, Y3%~4%. Such as white warm, three-color version of the dot value can also be close to the ratio, but must not lack a color version, otherwise it will be color cast, dew.

The black objects in the color photography image often cause black opacity due to the influence of the ambient color. When processing, first understand the adjustment of texture characteristics of various black objects, such as black steel, black leather clothing, black hair, etc., and their texture characteristics are different, and adjustments should be different. Such as black steel metal objects, to express its sense of weight, the setting should be based on the black version, outlet value up to 90%, while the three primary colors for the right amount removed, the sum of the four-color version is about 320%. As for the black leather clothing and other objects, it mainly displays its smooth and delicate light texture. When scanning, the four-color version must be soft and delicate, and the contrast should not be too large. The sharpness should not be over-emphasized.

In actual production, the black color of the object is not pure due to the dark color of the photographic image. It should be noted that the three-primary version achieves the effect of neutral black, and then the black version is dominant, so as to achieve a pure black effect and better express the texture level of the black object.

The dark tone of the artistic art picture is an important part of the image art. The black color varies greatly due to the different features and styles of various paintings. The scanning settings should be handled differently. For example, the Chinese painting is mainly ink, and the ink is pure. , Make the entire picture rich, long tone black version up to 95% ~ 98%. The color ink paintings, whether heavy or light colored, should reach 90%-95% black, 65%-70% green, 55%-60% red and yellow, and a total of four colors ranging from 270% to 285%.

Handle people's skin color. There are many problems with the reproduction quality of portrait images in many books, advertisements, and albums. For example:

Some skin colors are seriously distorted, and some of the face color has become orange, red brown, and some have become blue, gray and black.

Some skins are rough, hard and disjointed, and there is no continuous transition between light, medium, and dark tone, causing the dark part to reverse, and the yellow and red versions are shallow, forming a deep black plate.

In addition to some of the original document itself, it is mainly due to the improper setting of scanning separation parameters and improper color processing. The general solution is:

a. Determine the tone of the skin tone. When performing character scanning and color separation, we must deal with the characteristics of various people's skin color. First, determine the tone of the skin color by its age, gender, occupation, origin, ethnicity and other characteristics. For example, female skin color should be white and delicate, delicate and ruddy. Only when the key tone is correct, there will be no large color distortion; b. Control the skin color of the dark part is not reddish. The dark tone of most manuscripts is set by the black field. The Y and M color plates are darker, and the dot value reaches about 85%, sometimes reaching 90%. The C color version has a color-dyeing effect on the red tea color, which tends to be too large. Therefore, for a darker skin tone with a larger area, it is necessary to pay attention to controlling the Y, M version below 80%, generally 75% ~ 78%, C color version slightly deepened, while the K version of the tone slightly extended to Make up for the inadequacy of the C version; c. Grasp the continuous transition tone of skin color. Should be able to grasp the facial skin tone from the bright part to the tone part to the dark tone part of the tone should have a continuous transition, can not be hard disjointed, especially the M color version of the tone to be soft coordination; d. Under normal circumstances, the yellow version of the high light calibration To stay in the red version, the middle face of the skin tone should be controlled below 50%, and the black and blue plates should be moderately controlled to keep the warm tone.

Standardization of color management

Some color prints have poor color processing and cannot restore the original color tones. It is often seen that in order to make the screen visually colorful and disregarding the coordination relationship between colors, the unity law is very pure, heavy, and absolutely unique. In this way, although the effect is brilliant, the entire screen appears disorganized and unstructured. This is the current phenomenon that most operators only look at the colors on the computer screen, and only rely on arbitrary adjustments. This is a relatively common phenomenon.

Doing a good job of standardization and data-based color management is the most important basic work.

● Based on the plate making and printing equipment of the company, according to the national industry standards, through production exploration, the technical parameters and quality standards of photoprinting, film printing (CTP), printing, proofing, printing, and materials are reasonably formulated. And make it possible to connect and stably complete batch high-fidelity replication of images.

● Use standard gray scales, color scales, densitometers, and manuscripts for color reproduction tests to establish a set of gray balance parameter sets to ensure that gray and polychromatic colors in originals can be accurately restored.

● Create a color correction quasi-correction amount based on the input gray balance to achieve the reduction of R, Y, G, C, B, M six hue to ensure the true reduction of original color. After doing the above work, when scanning color separation, as long as the correct black and white field settings are used, the original color tone can be restored, and it is unnecessary or rarely necessary to perform post-processing. Instead, it is adjusted using Photoshop software tools to satisfy the customer only. The requirements were adjusted for some defects in the manuscripts or the use of special effects and printability.

To get out of the current error of image scanning color separation operations. The high-end professional scanner as a simple input device, its powerful professional adjustment functions are not used or not well used, and the black and white field calibration, level adjustment, color correction, clarity of emphasis are all easy to use Photoshop software Tool adjustment, often the parameters of each adjustment are not uniform, will result in unstable quality. In our practice, we have the experience that pictures scanned by high-end scanners and high-end electric extensions can only be patched, cut or stunted, and can't adjust picture levels, colors and sharpness, nor can they be enlarged. It is a prerequisite for improving quality and efficiency.

For images with poor originals, senior map adjusters can be arranged to repair them. When necessary, according to the printability, after the communication with the customer, there is a certain degree of effect in the selection of proper contrast, sharpening, or feathering.

Four principles for dealing with defects such as insufficient local color saturation:

● Additions and subtractions cannot be excessive. First, the additive color of the basic color should not be too large. To maintain the level of the basic color, it is not possible to create a level-parallel level due to an excessive amount of color. Secondly, the color amount of the opposite color cannot be too large. To maintain the change in light and shade, light and shadow in color, Can cause the color to be simplistic due to overuse of the opposite color, and cannot preserve the original tone of the image.

● Maintain the relationship between the amount of color and the amount of light. When adjusting a certain color, the color amount of the bright-tuning portion cannot exceed the color amount of the midtone portion, and the color amount of the medium-adjustment portion cannot exceed the color amount of the dark tone portion, and the brightness and darkness of the color amount and the light amount level should be maintained. Shallow relationship.

● Master the spatial variation of color distance. When adjusting a certain color, it is necessary to grasp the law of change when the color expresses the spatial distance, and to consider from the aesthetic point of view the relationship between the depth of field, the overall and the local, and the main and the minor.

● Grasp the law of color change. When making color adjustments, attention should be paid to the coordination of the four parts of the light receiving surface, including highlights, bright surfaces, midtones, and dark surfaces.

Reprinted from: Print Design Network