Jian Wang SEIE-TJU jianwang@tju.edu.cn Fundamental Jian Wang SEIE-TJU jianwang@tju.edu.cn.

Presentation on theme: "Jian Wang SEIE-TJU jianwang@tju.edu.cn Fundamental Jian Wang SEIE-TJU jianwang@tju.edu.cn."— Presentation transcript:

1 Jian Wang SEIE-TJU jianwang@tju.edu.cn
Fundamental Jian Wang SEIE-TJU

2 Index Human Vision System CIE Chromaticity Diagrams Color Space

3 EYE AND COLOR 人眼成像过程 视觉 ＝ “视” ＋ “觉”

4 EYE AND COLOR electromagnetic spectrum 400nm~700nm

5 EYE AND COLOR Simplified representation of the human eye

6 EYE AND COLOR cones and rods

7 EYE AND COLOR Cones(锥状细胞) are concentrated 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。

8 EYE AND COLOR Approximately 65% of these cones are sensitive to red light, 33% to green light and 2% to blue light Absorption curves for the different cones have been determined experimentally

9 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 characterized 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 light. 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.

10 Receptoral Color Information
Hue Saturation Value H S I

11 Trichromatic Theory additive color mixture (Red, green, blue) and subtractive color mixture (cyan, magenta, yellow)

12 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 colors 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。

13 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。

14 Standard Color System Grassmann's First Law of color mixture: The quantities of primary colors R, G, B in 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 Grassmann's First Law of color mixture: (continuous color stimulus form).

15 Standard Color System The color stimulus standardized with S() produce the spectral tristimulus values 该式与上页ppt的式子的关系是什么？

16 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 该式与上页ppt的式子的关系是什么？

17 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 r＋g≤1, r, 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.

18 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 = X[X] + Y[Y] + Z[Z].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 Y[Y] 确定. 当 X = Y = Z 时,仍代表等能白光 E白.

19 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

20 CIE Chromaticity Diagrams

21 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

22 CIE Chromaticity Diagrams
Color gamut(色阶)

23 Color Space Color spaces indicate color coordinate systems in which the image values 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

24 Color Space

25 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.

26 RGB Color Space The primary colors (RGB) form the base vectors of a three-dimensional orthogonal (color)-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.

27 RGB Color Space The Transform from RBG to NTSC RGB->NTSC
The Transform of RBG to sRGB which is a standard color space sRGB for the Internet proposed International Color Consortium (ICC) RGB->sRGB

28 CMY(K) Color Space A subtractive color space which is consisted of subtractive primary colors cyan, magenta, and yellow as well as possibly an additional black It is used for color printing process. RGB color space and the CMY color space can be transferred through

29 CMY(K) Color Space

30 YIQ Color Space A color coordinate system used in NTSC television system. Y: luminance component. I (in-phase) and Q (quadrature) contain the entire chromaticity information that is also denoted as chrominance signal. Y signal contains by far the largest part of the information. I and Q are transmitted by a much shorter waveband

31 YIQ Color Space Y I Q

32 YUV Color Space The color television systems PAL and SECAM.
The Y component is identical with the one of the YIQ color space. The I and Q signals are determined from the U and V signals by a simple rotation in the color coordinate system.

33 YUV Color Space YUV also indicates a color space, in which U corresponds to the color difference red-blue and V to the color difference green-magenta. Y corresponds to the equally weighted (arithmetical) averages of red, green, and blue. Brightness normalization can be defined by

34 YUV Color Space Y U V

35 YCbCr Color Space The YCbCR color space is employed for the representation of color vectors in the area of digital video (such as JPEG and MPEG).

36 YCbCr Color Space Skin detection in YCbCr color space
R.L.Hsu, A.M. Mohaned, A.K. Jain, Face Detection in Color Images, IEEE Trans. on PAMI, 2002, 24(5),

37 Uniform Color Spaces A uniform color space is a color space in which same-size changes in the color coordinates also correspond to same-size recognizable changes in the visible color tones and color saturation. The international lighting commission CIE recommended the L*a*b* color space CIE 1976 (CIELAB) and the L*u*v* color space CIE 1976 (CIELUV) as an approximation of uniform color spaces. Both color spaces are derived from the XYZ standard color system (CIE XYZ primary system).

38 CIELAB Color Space CIE L*a*b* (CIELAB) 是惯常用来描述人眼可见的所有颜色的最完备的色彩模型。
Lab 经常用做 CIE 1976 (L*, a*, b*) 色彩空间的非正式缩写（也叫做 CIELAB，它的坐标实际上是 L*, a*和 b*）。 Lab 颜色被设计来接近人类视觉。它致力于感知均匀性，它的 L 分量密切匹配人类亮度感知。因此可以被用来通过修改 a 和 b 分量的输出色阶来做精确的颜色平衡，或使用 L 分量来调整亮度对比。 CIELAB用于表示反射的或透射的物体。

39 CIELAB Color Space Lab 色彩空间是颜色-对立空间，带有维度 L 表示亮度，a 和 b 表示颜色对立维度，基于了非线性压缩的 CIE XYZ 色彩空间坐标。 L* 表示亮度； a* 表示红减绿； b* 表示绿减蓝；

40 CIELUV Color Space 在表示感觉上均匀的色空间方面类似于CIELAB色空间的色空间。L*值表示亮度，u*和v*是色度坐标。CIELUV用于自己能发光的色源（如电视屏幕和计算机显示器）。

41 HSI Color Space In the HSI color space hue, saturation, and intensity.
Red is specified as a "reference color.", H = 0 and H = 360 correspond to the color red.

42 HSI Color Space One of the advantages of the HSI color space is the separation of chromatic and achromatic information. The existence of singularities is a disadvantage for the HSI color space. H I S

43 HSV Color Space The HSV color space, which is also called the HSB color space, is particularly common in the field of computer graphics. By projecting the RGB unit cube along the diagonals of white to black, a hexacone(六面锥) results that forms the topside of the HSV pyramid.

44 Opponent Color Spaces The opponent colors red-green and blue-yellow and likewise an antagonistically organized light-dark system. function [ output_args ] = Untitled( input_args ) %UNTITLED Summary of this function goes here % Detailed explanation goes here close all; clear all; LPR_type = 1; % 1: blue-white, 2: yellow-black, 3 white-black, 4: black-white color_image_data0 = imread('test100.bmp'); if LPR_type == 2 color_image_data = 255-color_image_data0; else color_image_data = color_image_data0; end gray_image = double(rgb2gray(color_image_data))/255.0; color_image = double(color_image_data)/255.0; [im_width, im_height] = size(gray_image) r_component = color_image(:,:,1); g_component = color_image(:,:,2); b_component = color_image(:,:,3); figure(1); subplot(2,2,1); imshow(color_image); title('²ÊɫͼÏñ'); subplot(2,2,2); imshow(r_component); title('r·ÖÁ¿Í¼Ïñ'); subplot(2,2,3); imshow(g_component); title('g·ÖÁ¿Í¼Ïñ'); subplot(2,2,4); imshow(b_component); title('b·ÖÁ¿Í¼Ïñ');%È¡ÖµÔÚ0-255Ö®¼ä£¬¿É¿¼ÂÇÔÚÁ½Çø¼ä·Ö±ð½øÐÐÀ­Éì rg_diff = r_component - g_component; y_component = (r_component+g_component)/2; by_diff = b_component - y_component; minmax_component = max(r_component(:), max(g_component(:), b_component(:))) - min(r_component(:), min(g_component(:), b_component(:))); minmax_component =reshape(minmax_component,im_width, im_height); figure(2); subplot(2,2,2); imshow(rg_diff,[]); title('r-g·ÖÁ¿Í¼Ïñ'); subplot(2,2,3); imshow(by_diff,[]); title('b-y·ÖÁ¿Í¼Ïñ'); subplot(2,2,4); imshow(1-minmax_component,[]); title('ÁÁ°µ·ÖÁ¿Í¼Ïñ');

45 I1I2I3 Color Space The color space depicts a feature model rather than a color space. It is used for color image processing, especially for image segmentation.

46 Color Difference in RGB Color Space
The opponent colors red-green and blue-yellow and likewise an antagonistically organized light-dark system.

47 Color Difference in the HSI Color Space
The opponent colors red-green and blue-yellow and likewise an antagonistically organized light-dark system.

48 Color Difference in the CIELAB and CIELUV Color Spaces
In the CIELAB and CIELUV color spaces the Euclidian distance is used for determining color distance .

49 Macbeth ColorChecker The Macbeth ColorChecker is frequently used for the calibration of color image processing systems It contains 24 matte color surfaces: the primary colors of the additive and subtractive color mixture as well as six achromatic colors (gray shades). The remaining colors adapt to our environment (a leaf color, two skin colors, and several sky colors. 色卡是自然界存在的颜色在某种材质（如：纸、面料、塑胶等）上的体现，用于色彩选择、比对、沟通，是色彩实现在一定范围内统一标准的工具 色卡广泛用于纺织，服装，摄影，印刷，包装行业 24色图像色彩再现色卡 ，为真实还原任何照明条件下任何介质上的图像色彩提供参照。

50 Macbeth ColorChecker

51 Thanks