Convert RGB Files to CMYK File Color Adjustment Techniques

With the digital industry becoming increasingly specialized and popular, digital photos have become an important source of print images. The digital photo taken by the digital camera is RGB color JPEG format. As we all know, we need to convert it to PHOTOSHOP to support printing CMYK TIFF format, but the quality of digital photos directly transferred from RGB to CMYK is always Not satisfying: if the color is not saturated, the lack of layers and contrast, the overall feeling of gray, flat, backlight part and tone, and even some low-end home digital camera automatic white balance and auto exposure function is not very good, in special circumstances or In the low light environment, there will be color casts and darkness, which requires us to make some adjustments to the picture. After a period of practice and exploration, the author summarized some simple techniques for converting RGB files into CMYK file color adjustments. Share them here.

one. Color Management Settings in Photoshop (take Photoshop 6.0 as an example)

Before we convert the RGB image to the CMYK image, we must set up the “color separation project” in Photoshop. This step plays a vital role. It will be decided to change to the CMYK color after the four-color version. Basic edition tone. Most of the pictures can be converted according to the default settings, but for some bad pictures, you can achieve better results by changing different settings, and lay a good foundation for the later adjustment of pictures and the quality of the final product.

First, press Ctrl + Shift + K to call up the Photoshop "Color Settings" dialog box (Figure 1), select "Custom CMYK" in the "Workspace" CMYK to bring up the "Custom CMYK" dialog box (such as Figure 2). On the dialog box we can see a color separation option bar with options such as color separation type, black print volume, total ink limit, UCA quantity, etc., and a gray curve graph, Photoshop default Set to: Separation type: GCR; Black print generation: Medium; Black ink limit: 100%; Total ink limit: 400%; UCA number: 0 (as in Figure 3), different settings of these options will affect After the RGB version is changed to CMYK, different settings for different pictures can be adjusted differently to achieve the best conversion version. To give a few simple examples, such as taking pictures of outdoor scenery under sunlight, digital photos in this environment are generally better in color, you can change the version to CMY 60 to 70%, K in 90 to 95% (use the default setting Can), and then through the curve and the optional color adjustment, the specific adjustment method we will introduce in the following content, and outdoor characters can be set to YMC70-80%, K90%, and for the darker Image We can set the color separation type as follows: the black version has a small amount of production, and the total amount of ink is limited to 370%. This way, the version transferred out is YMC90% or more and K85% or so. In short, the ratio of YMC and K to be transferred must be determined according to the number of black components in the picture. Color-rich CMY can be shortened. Color is not much. Black is the main component. Darker images can be fixed. The black version is shorter and closer to the basic version of the electricity.

Second, adjust the converted GMYK image

Photoshop's default settings transferred out of the tone is probably CMY60 ~ 70%, K90 ~ 95%, which is a long tone black tone, if you do not adjust the direct printing will appear color is not bright, the level is unknown, the contrast is not strong A product with little contrast. Our adjustment is to complete the process of short blacking from the long black tone to the electric time division. The reason why it is necessary for the transferred version to be short-tuned and not to turn the picture into long black tone is because it can To increase the space for color adjustment, to deepen the CMY ratio and reduce the K component to achieve the purpose of deepening color, enhancing contrast, pulling out levels, and displaying details. We can use the curve and optional colors in combination to convert long black to short black. First, add 60 to 70% of CMY to more than 90% and K to 85% of the black in the available colors. As shown in Figure 4). This step must be done in a selectable color. In the past, there were some erroneous ways to laze the CMY to 90% in the curve. This not only did not add the ideal color level but made the original YMC in the picture very heavy ( Such as: the sky, flowers, etc.) and reconciliation lost the original color level, and through the optional color lengthened CMY tone we can feel the color level has changed significantly, without losing the level of the original color. However, looking at the single-channel channel, we find that K is still relatively full, occupying the main level, and YMC is still not full, we can adjust the curve to make the CMY color heavier to replace the level of K, make the picture more colorful, more detailed The sense of hierarchy is better. First, the white part of the image is reduced by K (generally minus 10% is enough), and the second bright part (20 to 30%) is pressed to achieve the “skeleton black” effect (see Figure 5). The more middle-tone levels in the picture, the next step is to raise the middle adjustment body of CMY (see Figure 6), which enriches the overall color of the picture. Digital images are generally virtual, so you also need to increase the sharpness and texture of the image through the "USM sharpening" or "sharpening edges" in the filter.

For pictures that are relatively dark, you can use the method of changing the color from RGB to CMYK. Because the picture is dark, the details are not enough, and the color is not rich. The color has been overdone, and it is no longer necessary. Pull too much contrast, so when you convert, you can directly set CMY above 90% or K80%, which is more conducive to brightening images and pushing out more levels. To be able to transfer CMYK textures to a long tone, you must modify the Photoshop settings. As mentioned in the first point, set the color separation options to: Color separation type: UCR; Black volume: Less; Total ink Volume: 370% (Figure 7, in the side of the "gray curve" you can see the version of the change). For digital cameras, adjusting the white balance has a lot to do with the color temperature at that time. (The color that appears at different temperatures is the color temperature. When a black object starts to glow when it is heated, it turns into a dark red first, with temperature. Continuing to rise will turn yellow, then turn white, and eventually it will turn blue. This phenomenon is very common in everyday life.) Under different lighting conditions, the color of the objects being photographed will change. . If the white balance of the digital camera is not properly adjusted, it will lead to color cast. For this kind of color image without white balance, we only need to whiten the part of the curve that should be white in the image to ensure that the image is gray. Balance is OK. When encountering serious coloring pictures, the curve adjustment will be very large. In this case, be bold and careful, let go of the hand to correct the color cast, but be sure to pay attention to the control of the opposite color of various colors, while the amplitude Excessive adjustment will also increase the cost of the increase in the number of points and the loss of levels. Adjustments should be made in a good size.

In short, during the color adjustment process, the colorists carefully observe and carefully review the manuscripts to find out the reasons for the poor quality of digital pictures. The problem is not difficult to solve. At the same time, it also requires us to take into consideration all aspects in the adjustment process. Without disregarding each other, we will certainly be able to present high-fidelity digital pictures on paper. To remind everyone that RGB color mode and CMYK color mode are two distinct color modes, not RGB and CMYK can be freely converted and the color remains the same, each time there is a loss of detail and color gradation. The tone of a beautifully colored CMYK image converted to RGB and then back to CMYK is completely different, and there is no way to switch back to the original version, so the printed colors are quite different. Therefore, we should not convert CMYK diagrams to RGB, and when they are used, they will be returned to CMYK. This is an absolutely wrong practice and must be avoided. At the same time, we sincerely hope that the photographer can adjust the digital camera's state according to different ambient color temperatures when shooting digital pictures. Under special conditions, filters such as UV filters should be used to filter out unwanted blue light and polarized light in the environment (digital Most of the pictures are blue, and the color cast is mostly blue, which provides higher-quality digital manuscripts for printing. (Author: Shi Yong Liu Chenxi)