PS color mode

Color mode is the basic attribute of an image. Every picture has a color mode, and there can only be one color mode. Common color modes include

• Bitmap mode

• Grayscale mode

• Duotone mode

• HSB (indicating hue, saturation, brightness) mode

• RGB (indicating red, green, blue)

• CMYK (representing cyan, magenta, yellow, and black) mode

• Lab mode

• Index mode

• Multi-channel mode

• 8-bit or 16-bit mode

Image description, reproduction for each mode The principles of color and the number of colors that can be displayed are different.
Photoshop's color mode is based on the color model, and the color model is very useful for images used in printing.
You can choose from the following modes

• RGB (red, green, Blue)

• CMYK(Cyan, Magenta, Yellow, Black)

• Lab (based on CIE L*a*b)

• Grayscale

1.RGB mode
R(Red) represents red light, G(Green) represents green light, B(Blue) Represents blue light. By mixing the three colors in different proportions, most colors in the natural world can be obtained. So R\G\B are called the three primary colors of color light. The method of producing color in this way is called RGB.
Many colors seen in daily life are composed of the three primary colors of color light, such as televisions (computer monitors) Colorful images in nature, colorful colors in nature, electronic pictures taken by digital cameras, etc.
In Photoshop, each RGB color includes color values ​​0~255. A color is usually described by its numerical value. PS splits the R, G, and B colors in the RGB mode image
and stores them in the corresponding channels.
Press Ctrl+1, Ctrl+2, and Ctrl respectively. The +3 key combination can display 3 channels of red, green and blue at one time. Press Ctrl+~ to display the composite channel

2.CMYK mode

CMYK is a color mode based on printing ink. It has 4 color channels of cyan, magenta, yellow and black. The color of each channel is also 8-bit, and 256 medium brightness levels. The combination of 4 channels makes each pixel have 32-bit color capacity. Since the current manufacturing process cannot produce high-purity ink, the result of CMYK addition is actually a dark red, so a special black ink needs to be added to neutralize it.
CMYK mode is based on the humorous fiber optic absorption properties of printed paper. When white light strikes the translucent ink, part of the color spectrum is absorbed,
while another part is reflected back to the eye. Theoretically, a mixture of cyan (C), magenta (M) and yellow (Y) will absorb all colors and produce black
Therefore, CMYK mode is a subtractive color mode, which is formulated for the lightest (highlight) color The printing ink color has a lower percentage, while the percentage specified for the darker (shadow)
color is higher. For example, a bright red might contain 2% cyan, 93% magenta, 90% yellow, and 0% black. Because the complementary color of cyan is red, reducing the percentage content of cyan will increase the red component of its complementary color. Therefore, the CMYK mode relies on reducing one channel color to highlight its complementary color. , which is obviously in line with the physical principles;
The grayscale image of the CMYK channel and the RGB list. The RGB grayscale represents the brightness of the color and the CMYK grayscale represents the ink concentration. However, the two have different effects on the
light and dark in the grayscale image. Definition
RGB channel grayscale image represents whiter. Higher brightness, darker means lower brightness, pure white means the highest brightness, pure black means the lowest brightness
Whiter CMYK channel grayscale image means lower ink content, darker means higher ink content, pure white means complete No ink;


3.Lab mode
Lab mode is a device-independent color mode. It is a color representation system that is independent of various input and display input devices.
A Lab color value is unique at any time and on any device. It solves the problem of different colors displayed on different screens and different printing devices. Therefore, this color mode is widely used in the color management process. .
In Lab mode:

L represents brightness, the range is 0~100%.

a represents the color component that changes in the range from red to green, and the range is -120~+120.
b represents the color component that changes in the range from blue to yellow, and the range is -120~+120 .PS splits the L, a, and b colors in the Lab mode image
and stores them in the corresponding channels respectively


4. Bitmap mode
In the image mode, The color capacity of the image is 1 bit, that is, the color of each pixel can only be selected from two depth colors, either "black" or "white", and the corresponding image is also composed of many small black Composed of blocks and small white blocks.
Tips: A CMYK image or RGB image must be converted to grayscale before it can be converted to a bitmap, and cannot be converted directly

5. Duotone mode
Duotone mode can make up for the shortcomings of grayscale images. Although grayscale images have 256 gray levels, when printing output, every drop of the printing press
Ink can only express about 50 shades of gray at most, which means that if you print a grayscale image with only one black ink, the image will be very rough.
If you mix another, two or three color inks, because each ink can produce about 50 gray levels, theoretically at least
can express 5050 gray levels, so print The resulting two-tone, three-tone or four-tone images will appear very smooth. This method of printing by mixing several boxes of ink is called "overprinting".
Generally, two-tone overprinting should be printed with darker black humor and lighter gray humor. Black ink is used to express shadows, and
gray ink is used to express midtones and highlights. But more often, a black ink is combined with a color ink, and the color ink is used to express the highlight area. Use this A technique that slightly tints grayscale images.
Since duotone uses different color inks to regenerate different grayscales, duotone is treated as a single-channel, 8-bit grayscale image in PS.
In duotone mode, it cannot be used as in RGB, CMYK Access individual image channels directly like in Lab mode, but control the channel through the
curve in the duotone options dialog box

6. Grayscale color mode

Grayscale color mode It can fully express the dark information of the image and have rich and delicate tonal changes. When processing grayscale images, it is necessary to avoid merging layers to minimize the loss of brightness information. RGB or CMYK images can usually be converted to grayscale images


7. Indexed color mode

Indexed color mode generates 8-bit image files with up to 256 colors. When the image is converted to indexed color mode, PS will build a 256-color lookup table that can store the colors in the indexed image. If the devil color in the original image does not appear in the table, the program will select the closest one or

use dithering to simulate the color.
The advantage of index mode is that its files can be made very small while maintaining a unique visual quality. It is very suitable for multimedia animations and web
pages. Only limited editing can be done in indexed color mode, for further editing you should temporarily convert to RGB mode. Indexed color files can
be stored in formats such as PS\BMP\GIF\EPS\PSB\PCX\PDF\RAW\PICT\PNG\TARGA or TIFF.

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