Color adjustment of digital photos in printing
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With the increasing professionalization and popularization of the digital industry, digital photos have gradually become an important source of printed images. The digital photos taken by digital cameras are RGB in RGB format. As we all know, we need to convert them into PHIFFs that support printing in PHOTOSHOP, but the quality of digital photos that are directly transferred from RGB to CMYK is always Not satisfactory: such as color is not saturated, lack of layers and contrast, overall feeling gray, flat, backlight part and tone, and even some low-end home digital camera automatic white balance and automatic exposure function is not very good, in special circumstances or In the low light environment, there will be color cast and darkness, which requires us to make some adjustments to the picture. After a period of practice and exploration, the author summarizes some simple usage techniques for converting RGB files into CMYK file color adjustments, and share them with you here.
First, Color management settings in Photoshop (take Photoshop 6.0 as an example)
Before we can convert RGB images to CMYK images, we must set up the "color separation" "color separation" in Photoshop. This step plays a crucial role, it will decide to convert to CMYK color after four color version. Basic version. Most of the images can be converted according to the default settings, but for some bad images, you can achieve better results by changing different settings, and lay a good foundation for the later adjustment of the image and the quality of the final product.
First, press Ctrl+Shift+K to bring up the Photoshop “Color Settings” dialog box. In the “Workspace” CMYK, select “Custom CMYK” to bring up the “Custom CMYK” dialog box. On this dialog box, we will You can see a color separation option bar with options such as: color separation type, black version generation, total ink limit, UCA number, and a gray curve. Photoshop defaults to, color separation type: GCR; black Version production: medium; black ink limit: 100%; ink total limit: 400%; UCA number: 0, different settings of these options will affect the tone from RGB to CMYK, different shades for different pictures , to adjust the various settings to achieve the best conversion version. To cite a few examples, such as shooting landscapes under outdoor sunlight, digital photos generally have better color in this environment. You can convert the version to CMY at 60-70% and K at 90-95% (using the default settings) Yes), and then adjust through the curve and optional color, the specific adjustment method will be introduced in the following content, and the outdoor characters can be set to YMC70-80%, K90%, and for the darker For the picture, we can set the color separation type to be: the black version is less generated, and the total amount of ink is limited to 370%, so that the converted version is more than 90% of YMC and about K85%. In short, the ratio of YMC and K that is transferred must be determined according to the black component in the picture. The color can be shortened by CMY. The color is not much black. The main component of the picture is darker. CMY can be fixed. The black version is short, close to the basic version of the electricity.
Second, adjust the converted GMYK picture
The default setting of Photoshop is about CMY60~70%, K90~95%. This is a long black tone. If you don't adjust it, the direct printing will show the color is not bright, the level is unknown, the contrast is not strong. Products with little contrast. Our adjustment is to complete the process of short-tune black that is used from long black to electric. The reason why the converted version is set to short black is not directly changed to long black. Leave a weighting space for the color adjustment by deepening the CMY ratio and reducing the K component to achieve the purpose of deepening the color, increasing the contrast, pulling out the level, and expressing the details. We can convert the long black to the short black by using the curve and the optional color. First, add 60 to 70% of the CMY to more than 90% in the black of the optional color, and K is reduced to about 85%. This step must be done in the optional color. In the past, there were some mistakes in the process of adding CMY to 90% in the curve. This not only did not add the ideal color level, but made the original YMC already heavy in the picture. Such as: sky, flowers, etc.) and reconciliation and loss of the original color level, and by the optional color lengthening CMY version of the tone we can feel the color level has been significantly improved, without losing the original color level. But looking at the single channel, we found that K is still full, occupying the main level, and YMC is not full enough. We can adjust the curve to make CMY color increase to replace the level occupied by K, making the picture more colorful and richer in details. The sense of hierarchy is better. First, reduce the K of the white part of the image (usually 10% is enough), and the second bright part (20~30%) is pressed to achieve the effect of "skeleton black", which can show more middle in the picture. The level of the hue, and then the CMY intermediate adjustment body up, which enriches the overall color of the picture. Digital pictures are generally virtual, so you need to increase the sharpness and texture of the picture by using “USM Sharpen” or “Sharp Edge” in the filter.
For the darker picture itself, you can use the method of directly changing from RGB to CMYK long black, because the picture is dark, the details are not much, the color is not rich, the contrast is not too big, the color is overdone, no longer need to Pull too much contrast, so you can directly set CMY to more than 90% K80% when converting, which is more conducive to the picture to brighten and press more levels. If you want to transfer the CMYK pattern to the long black, you must modify the Photoshop settings. For example, the method mentioned in the first point sets the color separation option to: color separation type: UCR; black version generation amount: less; total ink Amount: 370%. 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 after being heated, it will first turn dark red, with temperature Continue to rise will turn yellow, then turn white, and finally turn blue, this phenomenon is very common in daily life), under different light conditions, the color of the object will change . If the white balance of the digital camera is not adjusted, it will lead to photo color cast. For this kind of color cast image without white balance, we only need to whiten the part of the curve that should be white to ensure the gray image. The balance is OK. When encountering a picture with severe color cast, the amplitude of the curve adjustment will be very large. In this case, you should be bold and careful, and let go of the color correction of the hand, but you must pay attention to the control of the opposite color of various colors, and the amplitude. Excessive adjustments will also pay for the increase in dryness and the loss of tiers. The size should be adjusted when adjusting.
In short, the colorist in the process of coloring, carefully observe, carefully review the draft, to find out the reasons for the poor quality of digital pictures, the problem is not difficult to solve. At the same time, we also require us to take into account all aspects of the adjustment process, do not care about this loss, you will be able to put digital pictures on the paper. To remind everyone that RGB color mode and CMYK color mode are two distinct color modes. It is not that RGB and CMYK can be freely converted and the color remains unchanged. Each conversion will have some details and color levels lost. The color of a very beautiful CMYK picture converted to RGB and then back to CMYK is completely different, and there is no way to turn back to the original version, so the printed colors are very different. So everyone should not convert the CMYK diagram to RGB, and then switch back to CMYK when it is used. This is an absolutely wrong approach and must be avoided. At the same time, we also sincerely hope that photographers can adjust the state of digital cameras according to different ambient color temperatures when shooting digital pictures. Under special conditions, color filters such as UV mirrors should be used to filter out blue and polarized light that should not be in the environment. Most of the pictures are blue-blue, and the color cast is mostly blue. It provides a higher quality digital manuscript for printing.

