基于TCS230颜色传感器的色彩识别器的设计-外文翻译

Sensing color with the TAOS TCS230The TAOS TCS230 is a small, highly integrated color sensing device packaged in a clear plastic 8-pin SOIC. It reports, as analog frequency, the amount of shortwave (blue), mediumwave (green), longwave (red), and wideband (white) optical power incident onto the device. It can be used in a variety of color sensing applications. Details of the device can be found in its datasheet. This white paper details the concepts and calculations involved in color sensing using the TCS230. We will use the ColorChecker chart as an optical stimulus to work through a numerical example of color sensing. The chart, depicted in Figure 1, is manufactured and distributed by GretagMacbeth. The chart measures approximately 13 inches by 9 inches (330 mm by 230 mm); it contains 24 colored patches arranged in a 6 by 4 array. Figures 2 through 5 overleaf show the spectral reflectance of the patches in each of the four rows of the chart that is, the fraction of incident light that is reflected (with respect to an ideal diffuse reflector), as a function of wavelength from 350 nm to 750 nm.Figure 1 The ColorChecker contains 18 colored patches and a 6-step gray series.Figure 2 ColorChecker spectra, top row.Figure 3 ColorChecker spectra, second row.Figure 4 ColorChecker spectra, third row.Figure 5 ColorChecker spectra, bottom row (neutral series)Figure 6 Cone sensitivities of cone photoreceptors are shown. The shortwave-sensitive photoreceptors are much less sensitive than the other two types. The responses of the mediumwave and longwave photoreceptors have a great deal of overlap. Vision is not sensitive to the precise wavelength of the stimulus: What atters is optical power integrated under each response curve.Introduction to color vision Photoreceptor cells called cones in the retina are responsible for human color vision. There are three types of cone cells, sensitive to longwave, mediumwave, and shortwave radiation within the electro-magnetic spectrum between about 400 nm and 700 nm. Because the cone sensitivities are very roughly in the parts of the spectrum that appear red, green, and blue, color scientists denote the cell types as , and , the Greek letters for r, g, and b. (To denote the sensors R, G, and B would wrongly suggest a closer correspondence.) Estimates of the spectral response of the cone types are graphed in Figure 6 above.Light in the physical world can be characterized by spectral power distributions (SPDs). Colored objects can be characterized by spectral reflectance curves, such as those of the ColorChecker. However, vision is insensitive to the exact wavelength of a stimulus: According to the modern theory of color science, all that matters is the integral of optical power underneath each response curve. That there are exactly three types of cone cells leads to the property of trichromaticity: Three components are necessary and sufficient to characterize color. Some people might use the phrase “color as sensed by the eye,” but I con-sider that qualifier to be redundant at best, and misleading at worst: Color is defined by vision, so there is no need to use the qualifying phrase “as sensed by the eye,” or to use the adjective visible when referring to color.Overview of CIE Colorimetry The spectral responses of the cone cells that I graphed in Figure 6 were unavailable to researchers in the 1920s. Researchers at the time used psychophysical experiments, such as the famous color matching experiment, to tease out the data. The CIE is the international body responsible for color standards. In1931, that organization adopted the color matching functions denoted x (), y (), and z (), graphed in Figure 7.Figure 7 CIE 1931, 2 color-matching functions. A camera with 3 sensors must have these spectral response curves, or linear combinations of them, in order to capture all colors. However, practical considerations make this difficult. These analysis functions are not comparable to spectral power distributions!Weighting a physical SPD under each of these three curves (that is, forming the wavelength-by-wavelength product), and summing the results, forms a triple of three numbers, denoted X, Y, and Z. In continuous mathematics, three integrals need to be computed; in discrete math, a matrix product is sufficient. The X, Y, and Z tristim-ulus values characterize color. They are linear-light quantities, propor-tional to optical power, that incorporate the wavelength sensitivity of human vision. The Y value is luminance, which is ordinarily expressed in units of candela per meter squared (cdm-2). If you are measuring reflectance, the reflected tristimulus values depend upon the spectral characteristics of the illuminant, and their amplitudes scale with the power of the illumination. Relative luminance is the ratio of reflected luminance to the luminance of the illumination; it is also known as the luminance factor.Figure 8 SPDs of various illuminants are graphed here. Illuminant A, shown in orange, is representative of tungsten light sources; it is deficient in shortwave power, and may cause errors in sensing blue colors. The blue line graphs the SPD of a Nichia white LED. There is a peak in the blue portion of the spectrum: Uncorrected, the sensor would report excessive blue values. The other four lines represent CIE standard illuminants C, D50, D55, and D65.In many applications, tristimulus signals (including luminance) scale with the illumination, and are otherwise uninteresting in themselves. What is more interesting is the ratios among them, which characterize color disregarding luminance. The CIE has standardized the projective transformation of Equation 1, in the margin, to transform X, Y, Z values into a pair of x, y chromaticity coordinates that represent color disregarding luminance. These coordinates are suitable for plotting in two dimensions on a chromaticity diagram.x=X/(X+Y+Z) y=Y/(X+Y+Z) Eq 1 Chromaticity coordinatesIllumination A nonemissive object must be illuminated in order to be visible. The SPD reflected from an illuminated object is the wavelength-by-wave-length product of the illuminants SPD and the spectral reflectance of the object. Before light reaches the eye, the interaction among light sources and materials takes place in the spectral domain, not in the domain of trichromaticity. To accurately model these interactions requires spectral computations. When applying the TCS230, attention must be paid to the spectral content of the illumination and to poten-tial interaction between the illumination and the samples to be sensed. Generally, the less spiky the spectra, the better. Figure 8 graphs several illuminants.Your application may involve sensing color, in which case the preceding description applies. However, some applications of the TCS230 involve not so much estimating color as seen by the eye but rather sensing physical parameters associated with optical power in the visible range. In such applications, to approximate the visual response may not be the best approach: It may be more effective to take a more direct approach to estimating the parameters of the underlying physical process.The Color Checker Equipped with knowledge of how spectra are related to colors, the plotting of chromaticity coordinates, and the dependence of colors upon illumination, we can return to the ColorChecker. GretagMac-beth doesnt publish or guarantee the spectral composition of the patches of the ColorChecker. However, nominal CIE X, Y, Z values are published. The patches in the bottom row of the ColorChecker contain neutral colors; the numeric notations in the legends of Figure 5 reflect one tenth of the lightness (L*) values of those patches.The spectra graphed on pages 2 and 3 represent the physical wave-length-by-wavelength reflectance of the patches. These spectral reflec-tances have been measured by color measurement instrument called a spectrophotometer. If you had access to a light source having perfectly even distribution of power across the visible spectrum, then the reflectance curves graphed here could simply be scaled to repre-sent the reflectance in your application. Practical light sources do not have perfectly even spectral distributions, so compensation is neces-sary: You must compute the wavelength-by-wavelength product of the illuminants SPD with the spectral reflectance of the chart.We will first calculate the CIE X, Y, Z values from the chart. (These values should agree with the figures provided by Gretag.) Then we will calculate the R, G, B values that will be detected by a TCS230.To calculate CIE X, Y, Z, we take the 313 matrix representing the color matching functions (CMFs) of the CIE Standard Observer, and perform a matrix product with 31 spectral response values as corrected for illumination. This produces the X, Y, Z tristimulus values. When chromaticity coordinates x, y are computed from X, Y, Z through the projective transform in Equation 1, then plotted, the chromaticity diagram in Figure 9 results. The horseshoe-shaped figure, closed at the bottom, contains all colors: Every non-negative spectral distribution produces an x, y pair that plots within this region. The lightly-shaded triangle shows the region containing all colors that can be produced by an additive RGB system using sRGB (Rec. 709) primary colors. This region typifies video and desktop computing (sRGB). The points plotted in Figure 9 are the colors of the ColorChecker. White and gray values are clustered near the center of the chart.Figure 9 Coordinates of ColorChecker patches are graphed on the CIE x, y chromaticity diagram. The horseshoe encloses all colors; the triangle encloses the colors that can be represented in video (Rec. 709) and in desktop computing (sRGB).The TCS230 Figure 10 shows the responses of the four channels of the TCS230. The black curve shows the response of the unfiltered sensor elements. The red, green, and blue curves show the responses of the longwave-sensitive, mediumwave-sensitive, and shortwave-sensitive elements respectively.As I mentioned on page 5, the CIE model of color vision involves inte-grating an SPD under the X(), Y(), and Z() color matching func-tions (graphed in Figure 7), producing X, Y, and Z values. To use the TCS230 to estimate color we perform an analogous calculation, but using the TCS230 sensitivity functions instead of the CIE CMFs: We integrate the SPD under the TCS230s sensitivity curves, and produce R, G, and B values. The device R, G, and B values will depend upon several factors: the spectral content of the illuminant, the spectral reflectance of the sample, the spectral attenuation of any intervening optical components (such as the lens), and finally, the spectral response functions of the TCS230. The various spectral phenomena are modelled by computing wavelength-by-wavelength products.Figure 10 TCS230 spectral sensitivities are graphed here. The red, green, and blue channels are graphed in the corresponding colors; the gray line reflects the sensitivity of the clear (unfiltered) channel. Because these responses are different from the CIE standard observer, the values reported by the TCS230 are not colorimetric. However, suitable signal processing yields color information that is sufficiently accurate for many industrial applications. Owing to the fact that the TCS230 is sensitive to infrared light (having wavelengths above 700 nm), and the fact that most light sources produce power in the infrared region, typical applications include an IR cut filter in front of the TCS230. Figure 11 overleaf shows the response of a typical IR cut filter.To form a more accurate estimate of color requires processing the raw TCS230 R, G, and B values through a linear 33 matrix whose coeffi-cients are optimized with respect to the spectrum of the illuminant, the spectral response of intervening optical components, and the response curves of the TCS230. The data processing operation can be represented in matrix form as follows:x=Mt Eq 2The symbol t represents a three-element vector containing the device values captured from a color patch. M represents the 33 color correction matrix that we will apply to these values through matrix multiplication, denoted by the symbol. The symbol x represents the resulting vector of estimated X, Y, Z values.We can use matrix notation to symbolize processing a set of three color patches at once, by arranging the three sets of device values into successive columns of a 33 matrix T. Successive rows of T contain red, green, and blue data respectively. Upon matrix multiplication by M, the columns of the resulting matrix X contain XYZ values of the successive samples; the rows of X contain X, Y, and Z values respec-tively. One equation expresses the mapping of three patches at once:X=MT Eq 3Given a matrix T whose columns contain three sets of device samples, and a matrix X containing the corresponding set of three ideal XYZ triples, there is a unique matrix M that maps from T to X. It is found by computing the matrix inverse of T, then computing the matrix product (by premultiplication) with X:M=X T-1 Eq 4The resulting 33 color correction matrix M exactly maps the each of the chosen three sets of device values to the corresponding set of tris-timulus values. It is not necessary to invert matrices at the time of sensing! The matrix M can be computed in advance, based upon the samples that are expected to be presented to the sensor in the intended application. To process three device values upon sensing a sample, all that is necessary is computation of the matrix product of Equation 3.A color correction matrix that produces good results across more than three samples can be computed through a numerical optimization procedure. When this is done, no particular sample is likely to map exactly to its ideal tristimulus set, but a linear matrix can be constructed that minimizes the error across a range of samples (where the error is measured in a least-squares sense). The color correction operation is still accomplished exactly as in Equation 2.基于TAOS公司的TCS230的颜色感应TAOS公司的TCS230是一个小的、高度集成、8引脚、SOIC封装的色彩传感装置。它以模拟频率的方式输出短波（蓝色）、中波（绿色）、长波（红色）、宽带（白）光功率的事件数量。它可用于各种色彩感应应用领域。该设备的详细资料中可以找到它的数据表。本白皮书详细介绍了色彩感应的概念和使用TCS230参与计算。我们将使用一个光学刺激方案的ColorChecker图表工作，通过检测的色彩数值例子。下图，在图1所示，是由GretagMacbeth生产和分配。图表长约13英寸，9英寸（330毫米230毫米），它包含了64阵列安排24色斑。到5背面图2显示了在图表的每一行四个补丁的光谱反射-即入射光被反射的那部分（相对于一个理想的漫反射）作为波长从350功能，纳米到750纳米。图1 ColorChecker色补丁包含18个和6步灰色系列图2 ColorChecker谱，第一行图3 ColorChecker谱，第二排图4 ColorChecker光谱，第三行 图5 ColorChecker谱，底排（中性系列）图6锥锥光感受器敏感性所示。短波敏感的感光细胞远远低于其他两种类型的敏感。中波和长波的感光细胞的反应有很大的重叠。视觉是不敏感，准确的刺激波长：什么是光功率下atters每个响应曲线综合。色觉简介所谓感光细胞在视网膜视锥细胞是人类色彩视觉负责。内有电磁频谱三种类型的视锥细胞，敏感的长波，中波，短波辐射及约400纳米之间和700纳米。由于锥敏感性在频谱的部分出现红色，绿色和蓝色的很粗糙，色彩科学家记为，以及希腊字母为R，G细胞的类型，和b （为了表示对传感器的R，G，和B将错误建议更密切的对应关系。）的圆锥体的谱反应的估计是在上面绘制图6。在物理世界的光，其特征是光谱功率分布（结构化产品说明）。彩色对象，其特征是反射光谱曲线，如在的ColorChecker的。然而，视觉不敏感，对刺激精确波长：根据现代色彩科学理论，最重要的事情是在每个响应曲线光功率积分。这恰有三种视锥细胞类型导致trichromaticity财产：三个组成部分是必要的和足够的特征颜色。有些人可能会用“感觉到的颜色的眼睛，“但我了CON - Sider的限定词是多余的，充其量，误导在最坏的情况：色彩是由视觉定义，所以没有必要使用合格的短语“因为感觉到的眼睛，“或使用的形容词时可见指颜色。概述Cie的比色法锥细胞，我在图6绘制光谱反应无法在20世纪20年代的研究人员。当时的研究人员使用，如著名的配色实验心理实验，以梳理出的数据。在CIE是国际机构，颜色标准。 In1931，该组织通过了颜色匹配函数记（）和Y（）和z（），在图7绘制。图7 Cie公司1931年2 色彩匹配功能。一个3传感器的相机必须具备以下的光谱响应曲线，或它们的线性组合，以捕捉所有的颜色。然而，实际的考虑作出这一困难。这些分析功能比不上光谱功率分布！加权根据这三个曲线每个物理社民党（即，形成了波长的波长产品），总结的结果，形成了三个数字三倍，记在连续数学的X，Y和Z，三积分需要计算，在离散数学，矩阵产品就足够了。在X，Y和Z tristim-汗国值特征的颜色。它们是线性光量，正比于光学力量，即纳入人类视觉波长的敏感性。 Y值是亮度，这是通常在每平方米坎德拉（光碟米- 2）为单位表示。如果你是测量反射率，反射的三刺激值取决于对光源的光谱特性，其幅度与规模的照明电源。相对亮度的反射亮度的照明亮度的比值，它也被称为亮度因素。图8是绘制各种光源结构化产品说明这里。 A光源，以橙色显示，钨光源是代表，它是在短波力量不足，可能会导致感应蓝色的错误。蓝线图的社民党的日亚白光LED。有一个光谱的蓝色部分高峰：裸时，传感器会举报过度蓝色值。另外四线代表Cie的，D50的，D55和D65的标准光源。在许多应用中，三刺激信号（包括亮度）与照明规模，并应在其他无趣自己。什么是更有趣的是它们之间的比例，所特有的颜色无视亮度。在CIE有标准化的公式1中的保证金射影变换，将其转化为一对的X，Y和Z值的x，y表示颜色的色度坐标无视亮度。这些坐标在二维色度图上绘制合适。x=X/(X+Y+Z) y=Y/(X+Y+Z) 公式1 色度坐标照明一个nonemissive对象必须是为了照明可见。社民党从一照物体反射的波长是按波长的光源产品的社民党和对象的光谱反射率。光线到达之前光源和材料之间的眼睛，相互作用发生在谱域的地方，不是在trichromaticity域。为了准确地需要这些相互作用的光谱模型计算。当应用TCS230，必须注意对光照光谱内容和电位- TiAl金属间的照明和样品被觉察的互动。一般来说，越尖的光谱，就越好。图8图数光源。您的应用程序可能涉及敏感的颜色，在这种情况下，前面的说明适用。然而，一些应用涉及TCS230没有这么多的眼睛所看到的，而是传感在可见光范围内光功率相关的物理参数估计的颜色。在这种应用中，近似的视觉反应可能不是最好的方法：它可能是更有效地采取更直接的方法来估计底层物理过程的参数。色彩检查如何光谱与颜色相关的知识装备，绘制色度坐标，对照明色彩的依赖，我们可以返回的ColorChecker。 GretagMac- Beth没公布或保证的ColorChecker补丁的光谱成分。然而，标称Cie的的X，Y和Z值被公布。在底行的ColorChecker补丁包含中性色，在图5中的神话传说中的数字符号反映十分之一的亮度（长*）值的这些补丁。光谱绘制2和第3页上表示物理波长由波长的反射率的补丁。这些光谱反射已测色仪测量tances称为分光光度计。如果你有机会访问光源具有完全的权力分配，甚至在整个可见光谱，反射率曲线则绘制在这里可以简单地扩展到repre，发送应用程序中的反射率。实践没有光源的光谱分布十分均匀，因此补偿neces-萨利：你必须计算与图表的光谱反射的光源的波长社民党按波长的产品。我们将首先从图表计算在CIE的X，Y和Z值。 （这些值应同意Gretag提供的数字。）然后我们将计算的R，G，B的，将由一TCS230检测值。为了计算Cie公司的X，Y和Z，我们把31 3矩阵代表职能的配色在CIE标准观察者（CMFs），并执行一个有31个光谱响应矩阵