Getting Started with Image Correction (3)
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At present, almost all image processing work is carried out on Photoshop software. Therefore, in order to obtain a satisfactory color correction effect, it is necessary to understand the characteristics and limitations of Photoshop color processing. The general version of Photoshop can be divided into 4.0 and 5.0. The biggest difference between the two versions is the compatibility in color management. Version 4.0 requires a plug-in plug-in for color management and is not very effective. Version 5.0 has a built-in color management function that supports ICC color profile specifications. It is also convenient to use version 5.0 when dealing with Internet-related graphics files. However, if your job is just to do color correction for magazine ads, version 4.0 is absolutely competent. With flaws and no interference from color management, you can focus on fine-tuning the color to achieve more perfect image control. If you still like to use version 5.0, please pay attention to the difference between version 4.0 and 5.0 in dot gain. For a dotgoin of the same value, version 5.0 must be multiplied by 0.65 to equal the actual dotgain of the same value of version 4.0.
Set color separation parameters
Regardless of whether your original is CMYK or RGB, setting the color separation parameters in Photoshop is very important. You may ask: If the original is already a CMYK file for color separation, why do you need to set the color separation parameters in Photoshop? The reason is that there are some color cast problems that cannot be completely solved in the CMYK space. You must use other color spaces, such as RGB or LAB, to get better results. Therefore, the image has the opportunity to be converted in different color spaces. If the color parameters are set incorrectly, the image will be corrupted during the conversion process. Therefore, it is important to set the correct color separation parameters.
The first thing to set is the total ink amount parameter. Since the paper can bear a certain amount of ink in a unit area, this value is generally not more than 350%. The specific value depends on the paper, ink, printing machine, and printing. Depending on the pressure and printing speed, you can consult your printing house, ask for specific values, or contact us for reference materials. As for Photoshop's factory setting is 400%, this value will definitely lead to a deep level of the layer of paste, do not use.
The second is the black version of the parameter, the black version is the soul of the four colors, the amount of the black version will affect the feeling of the whole picture. A heavy black version will make the printed image feel turbid. If there is no black version (CMY only), the picture will be flat and lacking depth. The general picture can choose GCR is the setting of light (short black version). This setting is equal to the black version as the skeleton of the whole picture, so that the picture looks more layered and does not feel turbid. Of course, if your picture needs a gray atmosphere, you can choose a heavier black version. In addition, if the main body of the picture is a metal object, the heavy black plate will make the metal object look more realistic.
Ink setting
The upper limit of the black version will affect the level of the dark level. This value is generally between 70% and 90%, depending on the paper used and the printing characteristics. For example, your picture is for magazine advertisements, and it is printed in a rotary machine mode. The total ink volume is set to 300%. In this case, the dark level limit is about 80C70M70Y70K (that is, the upper limit of the black version is 70%). It will turn black.
For most pictures used for magazine advertisements, SWOPcoated can be used for paper setting. As for ink type setting, Toyo will be more suitable for Hong Kong, if the printing paper characteristics you use do not match SWOP, or the ink is not Toyo. For the series, it is recommended that you do a little experiment to get the best paper and ink combination values.
The dot gain value can generally be set to 25%, and the gray balance (GreyBalance) is set to 1.0C, 0.95%, 1.0Y, and 0.92K (why these values can be ignored for future discussion). After completing these settings, you have a suitable Photoshop working environment. Now, you are ready to go.