Use the Photoshop channel mixer to adjust the image (1)
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In Photoshop 5.0 and later, there is a "Channel Mixer" tool under the "Adjust" menu in the "Image" - "Adjust" menu. Most people may rarely use it. Various professional media articles are also available. This tool is rarely described in detail. In fact, this is a very useful tool to make large corrections to images when certain channels lack color information. The Channel Mixer tool allows you to use the color information of one color channel to apply the color of other color channels, which is not possible with other adjustment tools. With this command, you can do the following:
1. Make a fruitful correction to the color cast phenomenon.
2. Select a different percentage from each color channel to create a high quality grayscale image.
3. Create high quality toned color images.
The channel mixer and the above points are described in detail below.
First, the working principle of the channel mixer
The channel mixer dialog is shown in Figure 1.
The channel mixer works by selecting a channel in the image as the processing object (ie, the output channel), and then performing addition and subtraction calculation according to the channel information of the image and other channel information to achieve the purpose of adjusting the image. Note that the color information added or subtracted comes from the same image location of the channel or other channel. That is, the image color information of a certain channel in space can be calculated by the current channel and other channel color information. The output channel can be any channel of the source image. The source channel is different according to the image color mode. When the color mode is RGB, the source channel is R, G, B. When the color mode is CMYK, the source channel is C. M, Y, K. In the figure, the CMYK color mode channel mixer takes the cyan channel as the processing object, that is, the result of the operation in the figure is only reflected in the blue channel, so the cyan channel is the output channel. The calculation in the figure is: the original color information of the cyan channel of all images (the slider is still at 100%), minus 32% of the yellow information of the same image position, plus the color information of the magenta channel with the same image position 22 %, then increase the dot size by 16%. Therefore, the output image has a percentage of cyan dots: C=C+Mx22%-Yx32%+16%. For example, the color of an image is C40%M50%Y30%K0%, and after the operation in the figure, the output is color C57%M50%Y30%K0%. The meaning of "constant" in the figure is: the information of this channel directly increases or decreases the percentage of the maximum value of the color representation, where 10% is actually 10% × 100%.
The channel mixer works only when the image color mode is RGB or CMYK. When the image color mode is LAB or other mode, it cannot be operated. The tools under RGB are shown in Figure 2.
Second, the operation of the channel mixer
1. Open "Image" - "Adjust" - "Channel Mixer".
2. Select the output channel, which is the channel you want to adjust.
3. Drag the slider of any source channel to the left to reduce the percentage of the channel in the output channel, or drag to the right to increase this percentage, or enter between -200% and +200 in the text box. The value between %.
4. Drag the slider to enter a value for the Constant option. This option adds a channel with different opacity to the output channel.
5. If you want to get a grayscale image, select Monochrome to apply the same settings to all output channels, creating a color image that contains only gray values. In an image to be converted to grayscale, the ratio of each source channel participating in the formation of gray can be separately adjusted. If you select and then deselect the Monochrome option, you can modify the blending of each channel individually to create a special-tone image.
6. Click "OK" to complete the operation.
Third, the use of channel mixer for image processing
1. Color image color adjustment
Figure 3 is a landscape image. At a glance, there is a problem with the color of the grass in the picture. The color of the grass is green and lacks green. So think of ways to increase the Y value in the grass color. In order not to affect other colors, it is generally convenient to use the optional color correction tool (Selective Color) for processing, with the cyan color as the processing object, and add the c in the cyan, see Figure 4. After performing the operation of FIG. 4 four times, the image becomes FIG. 5, and the effect is not very good. The reason is that in the color of the grass, the content of the Y dot is very small (for example, the color value of the representative point is C64% M24% Y7% K14%), in order to increase the Y dot on this basis. The size is more difficult.