[TA frost wolf \u may - "hundred people plan"] 2.1 color space

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How to describe color

Sad reminder of design post

Color transmitter

Color cognition ：
The light source is the point of birth , The light source emits light , Light passes through direct 、 Reflection 、 Refraction and other paths eventually enter the human eye .
But when the human eye receives light , The cells of the human eye produce a series of chemical reactions .
The resulting signal is transmitted to the brain , Finally, the brain has a cognitive perception of color .

2.1.1 The elements of light

The light source

A light source is an object that produces light .

wavelength

The wavelength is theoretically infinite , But the visible light of our eyes is limited .

Energy distribution

Light as a real matter , It has energy , The unit of energy is the joule , The light we perceive has different energies . A beam of light can be combined by multiple lights of different wavelengths .

Spectrophotometer

Spectrophotometer is used to describe the specific energy intensity of light , We know from the spectrophotometer that , Light energy is mainly concentrated in 550nm near ,（ The corresponding color is green ）
From this we can know that ：

1. Mixed wavelengths make up light , Splitting the rays creates a single wavelength light
2. The main concentration range of energy
   

The propagation of light

Light is reflected , Part of the energy is absorbed .
Through the analysis of energy distribution diagram, we can get ： Most of the energy absorbed by an object is 600nm about , That is to say, the light absorbed by the object is yellow and green .

2.1.2 Relative brightness perception

Lighting one lamp in a dark environment has a completely different effect than lighting a thousand lamps in a bright environment , The human eye's perception of brightness is equivalent to from 0 To 1 Again from 1 To 10.

The human eye HDR

The human eye can distinguish the different levels of high brightness clouds , It can also distinguish the similarities and differences of different objects in the shadow . But the human eye cannot guarantee that the two functions work at the same time .

Distribution of photoreceptor cells in human eyes

A simple division of the cells that the human eye perceives color , It can be divided into rod-shaped cells and vertebral cells
The rod-shaped lower package is responsible for sensing the brightness , Vertebral cells are responsible for sensing color ; The former is particularly sensitive to brightness , As long as there is 5~14 When a photon reaches a rod-shaped cell, it will produce a nerve signal , This can also explain why flash bombs can cause blindness , Strong light directly interferes with the most sensitive photoreceptor cells of the human eye .

Vertebral cell

These cells are specialized in sensing color , But they are further subdivided into L cells ,M cells ,S cells . The three kinds of cells are responsible for sensing different wavelengths , As shown in the figure ,L Perceive the red zone ,M Perceive the green zone ,S Perceive the blue zone .
LMS Corresponding RGB

The essence of the human eye

The essence of the human eye is the receiver of the light source . His function is to receive external light input , Output neuroelectric signals into the brain .

The calculus formula of the light received by the human eye

• C Value is the neuroelectric signal output by the function of the human eye
• S（λ） Express LMS The perceptual distribution of these three sensory cells
• I（λ） Represents the power spectrum distribution of the light source
• R（λ） Represents the absorbed power distribution of the reflected object

2.1.3 History of color space

stay 19 Many conjectures were put forward in the th century , The mainstream includes the following three ：

1. Human eyes have 100 A variety of color sensing cells
2. There are three kinds of human eyes for feeling RGB Color sensitive cells
3. There are three kinds of color sensitive cells in the human eye , Black and white , Red and green , Yellow and blue color sensitive cells .

Munsell Color system

Munsell Describe colors through color cards , The rotation angle represents the hue , The vertical direction represents brightness , From the center of the circle to the outside Munsell saturation .

CIE 1931 RGB Color Specification System

A transition

XYZ Color Specification System

there RGB Is the value in the previous coordinate , The color gamut horseshoe diagram can be obtained

On this basis , then Y（ brightness ） Introduce this coordinate system , To make up Yxy Color space .
There are still many deficiencies , The color distribution of the two-dimensional horseshoe diagram is uneven , So we expect a more uniform color space .

2.1.4 Custom color space

1. Color gamut （ The coordinates of the three primary colors , This forms a triangle ）
2. Gamma（ How to segment inside a triangle ）
3. White spot （ The middle point of the gamut triangle ）

Gamma

A way to sample colors .
When gamma =1 when , Equivalent to linear cutting , Easy to calculate , The computer is efficient , Easy to understand ：

But when computer storage and display hardware were not developed , Adopted gamma Mostly 2.2, Pictured ：

2.1.5 Common color space

Color model ： A method of describing or arranging colors using certain rules
give an example ：RGB、CMYK、LAB
Color space ： Meet at least three indicators ： Color gamut 、 White spot 、gamma
give an example ：CIE XYZ、Adobe RGB、sRGB、Japan Color 2001 Uncoated,US web Coated（ The latter two are based on CMYK Model building ）

summary

What is color space ？
Color space contains three basic elements ： Color gamut 、 White spot 、gamma, Defines the range of colors .
What is the visible light range of the human eye ？
Look at the picture 400nm-700nm Between , After Baidu, the result is 312nm to 1050nm Between them are visible light bands of human eyes . Usually visible light band refers to ：380nm to 780nm.