PS Basic knowledge: Image processing in the three-color principle, three primary colors

(i) three-color principle

In the physics class in the middle school we may have done the prism test, the white light through the prism is decomposed into a variety of color gradually transition of the color spectrum, the color is red, orange, yellow, green, green, blue, purple, this is the visible spectrum. One of the eyes of red, green, blue is the most sensitive, human eyes like a three-color receiver system, most of the color can be red, green, blue three colors in accordance with different proportions of the synthesis produced. The vast majority of monochromatic light can also be decomposed into red, green, blue and three colours. This is the most basic principle of chromaticity, that is, three primary-color principles. The three base colors are independent of each other, and no one base color can be synthesized in two different colours. Red, green and blue are the three primary colors, and these three colors are the most widely synthesized. The red, green, and blue three primary colors are combined in different proportions to synthesize the process color called the additive process color.

Red + green = Yellow

Green + blue = Cyan

Red + blue = Magenta

Red + green + blue = White

Yellow, cyan, magenta are mixed by two kinds and hue, so they are called add two times color. Other than that:

Red + cyan = White

Green + Magenta = White

Blue + yellow = White

So cyan, yellow, magenta are red, blue, and green complementary colors respectively. Since everyone's eyes have different feelings for the same monochromatic color, if we use the same intensity of the three-color mixture, assuming that the intensity of white light is 100%, this time the subjective feeling is that the green lights are the brightest, red, the blue is the weakest.

In addition to the additive blending method, there are subtraction blending methods. In white light, cyan pigment absorbs red and reflects cyan, yellow pigment absorbs blue and reflects yellow, magenta pigment absorbs green and reflects magenta. Is

White-red = Cyan

White-green = Magenta

White-blue = Yellow

In addition, if the cyan and yellow pigments mixed, in the white light, because the pigment absorption of red and blue, and reflect the green, for the mixing of pigments we say the following:

Pigment (yellow + cyan) = white-red-blue = Green

Pigment (Magenta + cyan) = white-red-green = Blue

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

The above is the subtraction process color, subtraction process color is to absorb the three primary colors of different proportions to form a different color. So there are cyan, magenta, yellow is called pigment tri-color. The blending color of three color pigments is widely used in painting and printing. In the three primary colors of the pigment, the red, green and blue tri-color is called the subtract two times color or the pigment two times color. In the subtraction two times the color has:

(cyan + yellow + magenta) = white-red-blue-green = Black

The color mode represented by the above additive blending tri-color is called the RGB mode, while the color pattern represented by the subtractive blending tri-primary principle is called the CMYK mode, which is widely used in the fields of painting and printing.

RGB mode is the most commonly used in drawing software a color mode, in this mode, processing the image is more convenient, and, RGB stored images than CMYK images to small, can save memory and space.

CMYK mode is a pigment mode, so it belongs to the printing mode, but in essence, there is no difference with RGB mode, but the way of producing color is different. RGB is the additive blending mode, and CMYK is the subtraction process color mode. For example, the display uses RGB mode because the display is an electron beam that emits light from the fluorescent material on the screen to produce color. When there is no light, black, when the light is added to the maximum white. And what about the printer? Its ink does not emit light of its own. Therefore, it is necessary to use subtractive method to solve the color of other light reflected by absorbing certain light waves.

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

HLS are hue (hue), luminance (brightness), saturation (saturation). Hue is the color of a property, it is essentially the color of the basic color, that is, we often speak of red, orange, yellow, green, green, blue, purple seven species, each representing a hue. The hue adjusts to change its color.

Brightness is a variety of colors of the graphic primary colors (such as RGB image of the primary color of R, G, b three or a variety of hue) of the intensity, brightness adjustment is also the adjustment of intensity. Brightness range from 0 to 255, divided into 256 levels. And we usually speak of grayscale images, that is, between pure white and pure black divided 256 levels of brightness, that is, from white to Gray, and then turn black. Similarly, in RGB mode is the primary color of the light and shade, that is, red, green and blue three primary colors, from shallow to deep.

Saturation is the colour of the color of the image. For each color there is an artificially defined standard color, and saturation is the physical quantity that describes the approximate degree of color to the standard color. Adjusting the saturation is to adjust the color of the image. When the saturation bar of an image is zero, the image becomes a grayscale image, and you can try to adjust the saturation button on the TV.

There is also the concept of contrast. Contrast refers to the difference between different colors. The greater the contrast, the greater the difference between the two colors, and the nearer the opposite. For example, a grayscale image to improve its contrast will be more black-and-white, adjust to the limit, into black-and-whites image, on the contrary, we can get a gray canvas.

We understand the principle of color, we will not be at a loss in image processing, and for the adjustment of color can be faster and more accurate.

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