Detailed explanation of six color overprint scheme

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Detailed explanation of the six color overprint scheme of CD copy (III)

supplement to six color ink

separating magenta and cyan tones enables us to stabilize the tone curve of silk printing without bending too much. We can control the loss of high-profile points and expand the dark level to enhance details. Because the use of 1/2 standard dot size in the dark tone, or four times the dot size in the bright tone, can ensure the normal operation of the machine and the same hue as four-color printing, which also greatly reduces the color drift

now that we have explained the basic theory of this color reproduction method and discussed its advantages in silk printing, it is time to officially use it. In the second part, we will study all the problems in production and the different technologies that we can use to copy with color separation. There are other problems, such as gray balance, color channel separation, color separation, selecting the number and angle of halftone lines, proofing, using dcs2.0 for output, printing color sequence, ink, and alignment line, etc

theory is applied to practice

it is the dream of every silk printer to accurately copy colors with a wide range of color gamut. However, it can be seen from the content of the first part that the limitations of the traditional four-color printing process in printing methods limit the realization of this dream

in order to solve the problems contained in four-color printing, it is necessary to find a non-traditional scheme without moire, a small amount of dot expansion and tone compression, so there is a six color overprint replication scheme. Expand the ink unit to six colors, that is, add two tones of magenta and cyan in addition to black and yellow. This method does increase the cost, but at the same time, we should also see the benefits of the scheme to the image

only when rubber is made into tires and on the road can we know its reliability. The same is true of the six color overprint scheme. Only practical practice can prove its usefulness. Here we will evaluate the color separation technology and see how some important problems are, including gray balance, color separation channel, number and angle of halftone lines, proofing, and using dcs2 0 for output, printing color sequence, ink consumption, registration, etc

when to use six color overprint

before dealing with the problem of color separation, it is best to determine whether the processed image is necessary or suitable for the use of six color reproduction scheme

there are two kinds of images that are most suitable for six color reproduction schemes (also known as two tone reproduction). The first is with darker details and full and rich colors, which are difficult to be obtained by traditional printing technology, and Zhengye International's revenue in that year also reached 2.074 billion yuan, such as black feather, dark wine, black bottle glass, walnut, reddish brown and other dark wood products. In traditional printing, in order to obtain these colors, black must be added to the color separation, but black suppresses the fine tone of the image, and the effect pursued will be erased

another image type is those with cubic color components in high-profile details or high-profile areas. Such images often appear in pop panels and similar extreme images. Examples of such images are water colored soap bubbles, shadows of white eggs, lace and details of white clothes, white clouds or barbecue food, etc. Natural color images such as flowing water, rocks, stones, beaches, feathers, bark, shells, leather, carved gemstones and ice are also the choice for two-tone reproduction

note that in an image, the possibility of extremely high light and extremely dark tone appearing at the same time is very small. Generally speaking, either extremely high light or extremely dark tone occurs. In addition, we should also remember that the two tone process is not omnipotent. Like other printing methods, it also has certain limitations. (i.e. the sample is kept in the jaw, in the jaw, in the parallel section or outside the gauge distance) the more details in the high-profile or dark tone area of the image, the more careful and serious it needs to be. Since the chromatic method is also used in six color reproduction, many colors that can be perceived by human eyes are still outside the color gamut or replicable range, especially the very bright green, purple and violet/magenta

for simplicity, focus on images with a large number of dark details and a large number of highlight colors and tertiary colors. These images are often problematic images in silk printing. Generally, there will be dark tone merging and high-profile dot expansion and too many moire. The color separation object used for testing here is the familiar Kodak Q60 test image

color separation

Photoshop is usually used for color separation. Before using six colors to work, you need to make some basic settings in the color separation setting dialog box. In windows and Mac OS, open the file color settings CMYK setup dialog box

there are several color separation settings in image color separation that need to be adjusted for six color separation. First, adjust the ink color and black version generation value in the CMYK setup dialog box

if the colorimeter or spectrophotometer is used, measure and record the l*a*b* value of each printing color, and enter it into the ink color box in Photoshop (open the ink options window). As far as this article is concerned, the measurement will not be carried out, but the default operator will recognize that the number is set to swop uncoded. Only highlight high-profile colors without darkening normal color separation inks. Here, the focus is on improving the fine soft tone of high-profile areas while maintaining the density of dark tone images

a key adjustment here is to set the black version generation in color separation. In order to make this setting, you need to open the color separation option window, select black generation to enter the black generation curve. The next step is to click 0% of the point (lower left corner) with the mouse and drag it to the right to 50% of the point. This means that there is no black version below 50%. At the same time, click the upper right corner and drag it down to 75%, so that the black version will not have a value greater than 75% in the darkest area of the image

the purpose of this is to make the image generated by chromaticity achieve gray balance at all hues. This is a typical background color removal (UCR) process, especially suitable for the brighter part of the image. It also reduces the amount of black plates attached to the darkest areas of the image

one advantage of color reproduction with double cyan and double magenta inks is that it reduces the amount of black ink required to replicate high-profile gray and dark gray and rich colors. By adjusting the curve, the black version is applied in the 3/4 tone area, and the other five colors are used to obtain clear gray and dark details

(to be continued)

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