Basic Course of PS Color: Understanding the Three Color Principle of Photoshop

When it comes to painting and images, it is natural to talk about color. All patterns are composed of basic shapes and colors. Color constitutes an important part of our image processing. Next, we will understand the principle of color, which will be our artBasics。

（1） Trichromatic principle

In the physics class of middle school, we may have done prism experiments. After passing through the prism, white light is decomposed into a variety of color spectrums with gradual color transition. The colors are red, orange, yellow, green, green, blue and purple in turn, which is the visible spectrum. The human eye is most sensitive to red, green and blue. The human eye is like a three color receiver system. Most colors can be used in different proportions through the three colors of red, green and bluesynthesisGenerate. Similarly, most monochromatic light can also be decomposed into red, green and blue light. This is the most basic principle of colorimetry, namely the three primary color principle. The three primary colors are independent of each other, and any primary color cannot be combined with other two colors. Red, green and blue are three primary colors, and the color range of these three colors is the most extensive. The three primary colors of red, green and blue are added in different proportions to form a mixed color, which is called additive mixed color.

Red+Green=Yellow

Green+Blue=Teal

Red+Blue=Magenta

Red+green+blue=white

Yellow, cyan and magenta are all mixed by two colors, so they are also called additive secondary colors. In addition:

Red+cyan=white

Green+magenta=white

Blue+yellow=white

So cyan, yellow and magenta are complementary colors of red, blue and green respectively. Because everyone’s eyes have different feelings about the same monochrome, if we mix the three primary colors with the same intensity, we assume that the intensity of white light is 100%. At this time, people’s subjective feelings are that green light is the brightest, red light is the second, and blue light is the weakest.

In addition to additive mixing, there is subtractive mixing. Under white light, cyan pigment can absorb red and reflect cyan, yellow pigment absorbs blue and reflects yellow, and magenta pigment absorbs green and reflects magenta. That is:

White red=cyan

White green=magenta

White blue=yellow

In addition, if cyan and yellow pigments are mixed, under white light, the pigments absorb red and blue, but reflect green. The mixing of pigments is shown as follows:

Pigment (yellow+cyan)=white red blue=green

Pigment (magenta+cyan)=white red green=blue

Pigment (yellow+magenta)=white green blue=red

The above are all subtractive mixing, which forms different colors by absorbing different proportions of the three primary colors. Therefore, cyan, magenta and yellow are called the three primary colors of pigments. The mixing of three primary colors of pigments is widely used in painting and printing. Among the three primary colors of pigments, red, green and blue are called subtractive secondary colors or pigment secondary colors. In subtractive secondary colors:

(cyan+yellow+magenta)=white red blue green=black

The color mode represented by the above three additive and mixed primary colors is called RGB mode, while the color mode represented by the three subtractive and mixed primary colors is called CMYK mode, which is widely used in painting and printing.

RGB mode is the most commonly used color mode for drawing software. In this mode, it is convenient to process images. Moreover, the image stored in RGB is smaller than CMYK image, which can save memory and space.

CMYK mode is a pigment mode, so it belongs to the printing mode, but it is not different from RGB mode in essence, except the way of producing color. RGB is additive mixing mode, and CMYK is subtractive mixing mode. For example, the display uses RGB mode, because the display is an electronic beam bombarding the fluorescent material on the fluorescent screen to emit bright light to produce color. It is black when there is no light, and white when the light reaches the maximum. And the printer? Its ink does not emit light of its own. Therefore, only by absorbing specific light waves and reflecting other light colors, we need to use subtractive method to solve this problem.

（2） HLS (hue, brightness, saturation) principle

HLS is Hue, Luminance and Saturation. Hue is an attribute of color. In essence, it is the basic color of color, that is, we often talk about red, orange, yellow, green, green, blue and purple. Each represents a hue. The adjustment of hue is to change its color.

Brightness is the brightness of the graphic primary colors of various colors (for example, the primary colors of RGB images are R, G, B or various self colors). Brightness adjustment is also the brightness adjustment. The brightness ranges from 0 to 255, and is divided into 256 levels. The gray image we usually talk about is 256 levels of brightness between pure white and pure black, that is, from white to gray, and then to black. Similarly, in RGB mode, it represents the brightness of the primary colors, that is, the brightness of the red, green and blue primary colors, from light to dark.

Saturation refers to the chromaticity of an image color. For each color, there is a manually specified standard color. Saturation is a physical quantity that describes the closeness between colors and standard colors. Adjusting saturation is to adjust the chroma of the image. When the saturation bar of an image is zero, the image will become a grayscale image. You can try to adjust the saturation button one by one on the TV.

Another concept is contrast. Contrast refers to the difference between different colors. The greater the contrast, the greater the difference between the two colors, on the contrary, the closer. For example, a grayscale image will be more black and white when its contrast is increased. When it reaches the limit of, it will become a black and white image. On the contrary, we can get a gray canvas.

If we understand the principle of color, we will not be at a loss in image processing, and we can adjust the color faster and more accurately.