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1、Fundamental,Jian Wang SEIE-TJU ,Index,Human Vision System CIE Chromaticity Diagrams Color Space,EYE AND COLOR,人眼成像过程,视觉 “视” “觉”,EYE AND COLOR,electromagnetic spectrum,400nm700nm,EYE AND COLOR,Simplified representation of the human eye,EYE AND COLOR,cones and rods,EYE AND COLOR,Cones(锥状细胞) are concen
2、trated around the fovea(中心凹) and are very sensitive to color with high spatial resolution Rods(杆状细胞) are more spread out and are sensitive to low levels of illumination with low spatial resolution.,人眼可以轻松区分上千种颜色，但在固定的光照条件下，只能区分约几十个灰度级。,EYE AND COLOR,Approximately 65% of these cones are sensitive to
3、red light, 33% to green light and 2% to blue light Absorption curves for the different cones have been determined experimentally,Receptoral Color Information,The colors that we perceive in our environment are divided into two classes: chromatic(彩色) and achromatic(灰度). The chromatic colors can be cha
4、racterized by three components: hue, saturation, and luminance Hue describes the type of chromaticity a color has and is indicated generally with words such as red, yellow, and blue. Saturation describes the purity of a color, or the measure of the degree to which a pure color is diluted by white li
5、ght. As saturation decreases, colors appear more faded. Luminance indicates the strength of light sensitivity as it is connected to each color sensitivity. The greater the strength of the lighting, the lighter the color appears.,Receptoral Color Information,Hue Saturation Value,H,I,S,Trichromatic Th
6、eory,additive color mixture (Red, green, blue) and subtractive color mixture (cyan, magenta, yellow),Metamerism,Metamerism(同色异谱) implies that two objects that appear to have exactly the same color may have very different colors under differing lighting conditions.,The wavelengths of the primary colo
7、rs C1, C2 , and C3 are standardized internationally. They are the spectral colors with the wavelengths 700nm (red), 546nm (green), and 435 nm (blue).,同色异谱现象简单来说就是颜色相同，而光谱组成不同。一种颜色的再现与观察颜色的光源特性有一定的关系，某两种物质在一种光源下呈现相同的颜色，但在另一种光源下，却呈现不同的颜色，这种现象就叫同色异谱现象。,Metamerism,同色异谱现象简单来说就是颜色相同，而光谱组成不同。一种颜色的再现与观察颜色的光
8、源特性有一定的关系，某两种物质在一种光源下呈现相同的颜色，但在另一种光源下，却呈现不同的颜色，这种现象就叫同色异谱现象。 现象1：现实生活中，在商场、超市购物时，在荧光灯下颜色一致的袜子或手套，买回家后在白炽灯下颜色却不一样了。 基于同色异谱油墨的印刷技术的货币防伪：在可见光波段，两种油墨视觉效果一致，而在紫外光照射下，两种油墨颜色不同，并且光谱特征也不一样，这样可以达到双重防伪的功效。,Standard Color System,Grassmanns First Law of color mixture: The quantities of primary colors R, G, B in
9、 the mixed color M are indicated by R, G, and B.,The quantities of primary colors can be assumed to be negative in the color blending,Grassmanns First Law of color mixture: (continuous color stimulus form).,Standard Color System,The color stimulus standardized with S() produce the spectral tristimul
10、us values,Color Matching Experiment,实验中有一个圆圈，分成两个部分，下半部是眼睛看到实物的颜色，上侧的半圆是RGB三原色的混色比例，适度调整可见到与下半圆相同的颜色，这就是RGB值。由于人类知觉感受的所有颜色，隐含的RGB值有负数，因此，若采用加法混色的方式，上半圆的颜色无法与下半圆的颜色相同。传统的电视的色彩空间，系依据阴极射线管的发光特性，不能显示RGB负值，计算机产品系的sRGB也相同,CIE Chromaticity Diagrams,由 R、G、B 三点连成的三角形称彩色三角形,其重心 E 即为等能白光 E白 的位置. 在彩色三角形内 rg1, r
11、, g, b 均为正值, 由三基色相加混合配出的各种彩色均在三角形内. (CRT),RGB 计色制的缺点 在色度图上不能直接表示出亮度, 不方便计算某色光的亮度. 混色曲线 r、g、b中有负值存在,计算和实际测量容易出差. 谱色轨迹不全在坐标的第一象限内,作图不方便.,CIE Chromaticity Diagrams,CIE 1931 色彩空间用X、Y和Z来表示颜色的三色刺激值.在 CIE XYZ 色彩空间中,三色刺激值并不是指人类眼睛对短、中和长波的反应,而是一组称为 X、Y 和 Z 的值,约略对应于红色、绿色和蓝色(X、Y 和 Z 值并不是真的看起来是红、绿和蓝色,而是从红色、绿色和蓝色
12、导出来的参数),并使用 CIE 1931 XYZ 颜色匹配函数来计算.,在 XYZ制中, 配色方程为 F = XX + YY + ZZ.三基色单位 X、Y、Z 满足的三个条件: 用它们配出实际彩色时,三个色系数 X、Y、Z 均为正值. 为了便于计算,使合成彩色光的亮度仅由 YY 确定. 当 X = Y = Z 时,仍代表等能白光 E白.,CIE Chromaticity Diagrams,x分量近似红色分量, y分量近似绿色分量 x=y=z,能量相等位置为白光 所有的单色光都位于蛇形图上, 全饱和。离边界越远、越接近等能量位置的点,饱和度越接近0 色度图中用任意两点的直线段定义所有不同颜色的变
13、化,这些颜色可以由这两点的颜色相加得到. 三点连接的三角形内的任何颜色都可以由三点颜色的不同混合产生. RGB系统使用的物理三基色及通过相加混色合成的颜色在蛇形图内部,CIE Chromaticity Diagrams,CIE Chromaticity Diagrams,CIE 1931色域(gamut)图,23个色域,等色调波长线和等饱和度线,CIE Chromaticity Diagrams,Color gamut(色阶),Color Space,Color spaces indicate color coordinate systems in which the image values
14、 of a color image are represented. The difference between two image values in a color space is called color distance.,Physics and Technics-based Color Spaces RGB, CMY(K), XYZ YUV/YCbCr/YIQ, CIELAB/CIELUV Perception-based Color Spaces : HSI/HSV/HSL/HSB Uniform Color Spaces : XYZ , CIELAB/CIELUV,Color
15、 Space,RGB Color Space,The most commonly employed color space in computer technology, especially in color display. It is based on the additive mixture of three primary colors Red, Green, and Blue.,RGB Color Space,The primary colors (RGB) form the base vectors of a three-dimensional orthogonal (color
16、)-vector space The origin (zero-vector) is represents black . Any color can therefore be viewed as a linear combination of the base vectors in the RGB space.,In RGB color space, a color image is mathematically treated as a vector function with three components.,RGB Color Space,The Transform of RBG to sRGB,RGB-NTSC,RGB-sRGB,The Transform from RBG to NTSC,CMY(K) Color Space,A subtractive color space which is consisted of subtractive primary colors c
