CIELAB color space

The 1976 CIELAB Color Space. Defiaed at the same time as the CIELUV space, the CIELAB space, propedy designated CIE E i , is a nonlinear transformation of the 1931 CIE X, Y, Z space. It also uses the metric lightness coordinate E, together with ... 

The frame-grabbed interferograms with a resolution of 512 pixels by 512 lines are first transformed from RGB to CIELAB color space and they are then converted to the him thickness map using appropriate calibration and a color... 

CIE color system, 7 304. See also Commission Internationale de l clairage (CIE) chromacity diagrams, 7 313-315 standard illuminants, 7 315-316 CIEDE200 color difference equation, 7 322 CIELAB, 7 304 CIELAB Color Space, 7 320 CIELAB color values, of flax fiber, 11 614t Cielab dye nomenclature system, 9 244 CIELAB Metric Color Spaces, 7 320 CIELAB system, 19 428, 451 CIELUV Color Space, 7 319-320 CIE Standard Observer, 7 311-312 Cigarette filters... 

The color difference is finally calculated as the geometrical distance between the two positions in the CIELAB color space ... 

Colors can be defined with the CIELAB color space. All colors are arranged in a circle around a central vertical lightness axis. The center of the hue circle is considered to be neutral gray and saturation is quantified by the distance from the axis. All colors can be defined in the color space by color coordinates [9.25]. 

Color Space system (ASTM 308 Standard) which is widely used in the industry. It provides 3 color readings that occupy the CIELAB color space L, a, and b values. ... 

The usual reference standard is the CIEXYZ color space or CIELAB color space (5,9). From this standard, other color spaces have been developed. 

G. Hoffinarm, CIELab color space, [electronic ] http //www. fho-emden.de/ hoffmann/cielab03022003.pdf, 2008. 

In a uniform color scale, the differences between points plotted in a color space correspond to visual differences between the colors plotted. The CIELab color space is organized in a cube form. The L axis runs from top to bottom. The maximum for L is 100, which represents a perfect reflecting diffuser. The minimum for L is zero, which represents black. The a and b axes have no specific numerical limits. Positive a is red negative a is green positive b is yellow negative b is blue [18]. 

Color measmements were performed on a Minolta CM-3700-d spectrophotometer. Measmements were made in CIELAB color space with illuminant D56, 10° observer and specular component included. 

In color technology and measurement, both types of approaches are used. Color printing, for example, generally employs three colors (usually plus black), and the ever useful CIE system was founded on experiments in which colors were matched by mixtures of three primary colors, often blue, green, and red. Yet transmitted television signals are based on the opponent system, with one intensity and two color-balance signals, as are the modern representations of color, such as the CIELAB and related color spaces based on red-green and yeUow-blue opponent axes. 

The 1976 CIE Metric Color Spaces. Both the CIELUV and CIELAB spaces can have their Cartesian coordinates converted to cylindtical coordinates, called metric or hue-angle coordinates, with E unchanged. These coordinates are designated CIE LYC h and CIE LYC, b, respectively. 

Hunter L,a,b and Other Color Spaces. The CIELAB and CIELUV color spaces were the outgrowth of a large and complex group of interrelated early systems and have replaced essentially all of them except for the 1942 Hunter Y,a,b group of color spaces (3). This was the earliest practical opponent-based system which is still widely used. In this system, for illuminant C and the 2° standard observer ... 

In the CIELAB and CIELUV color spaces, the difference between a batch sample and a reference standard designated with a subscript s, can be designated by its components, eg, AAL = L — L. The three-dimensional total color differences are given by EucHdian geometry as the 1976 CIE lYa b and 1976 CIE lYu Y color difference formulas ... 

There are instances in which one manufacturer may designate a bluish red dye as Red 4B and another manufacturer uses Violet 2R for the same dye. To resolve such a problem the manufacturers pattern leaflets should be consulted. These show actual dyed pieces of cloth so the colors of the dyes in question can be compared directly in the actual appHcation. Alternatively, colors can be specified in terms of color space coordinates. The Cielab system is becoming the standard in this system the color of a dye is defined by three numbers, the L, a, and b coordinates (see Color). 

Color Difference Evaluation. Shade evaluation is comparable in importance to relative strength evaluation for dyes. This is of interest to both dye manufacturer and dye user for purposes of quaUty control. Objective evaluation of color differences is desirable because of the well-known variabihty of observers. A considerable number of color difference formulas that intend to transform the visually nonuniform International Commission on Illumination (CIE) tristimulus color space into a visually uniform space have been proposed over the years. Although many of them have proven to be of considerable practical value (Hunter Lab formula, Friele-MacAdam-Chickering (FMC) formula, Adams-Nickerson formula, etc), none has been found to be satisfactorily accurate for small color difference evaluation. Correlation coefficients for the correlation between average visually determined color difference values and those based on measurement and calculation with a formula are typically of a magnitude of approximately 0.7 or below. In the interest of uniformity of international usage, the CIE has proposed two color difference formulas (CIELAB and CIELUV) one of which (CIELAB) is particularly suitable for appHcation on textiles (see Color). 

An important advantage of the CIELAB system is that the resulting color difference can be split up into component contributions, namely lightness, saturation, and hue, corresponding to the arrangement of the color space ... 

Work within the color community continued for the ideal, uniform color space. In 1976, the CIE recommended a more nearly uniform color space known as L a b with the official designation CIELAB. L a b is an opponent-type color space with rectangular coordinates similar to Hunter L,a,b. The L indicates lightness (0 to 100), the a indicates redness (+) and greenness (-), and the b indicates yellowness (+) and blueness (-). The limits for a and b values are around -80 and +80. The two color scales do not correlate and a color located in L,a,b space will be in a different location in L a b. ... 

There has been a growing interest in the food industry for a color space based on a polar model. In 1976 when CIELAB was adopted, the CIE recommended an alternative color scale known as CIELCH or L C H. Of the three dimensions of color, the hue is the most critical in terms of perceptibility and acceptability for normal color observers. The L C H color space identifies the hue as one of the three dimensions. A color is located using cylindrical coordinates with L being the same as in CIELAB and C and H computed from a and b. The coordinates of CIELCH (also see Fig. F5.1.11) are ... 

Many industrial color applications work with a color spectrophotometer to measure CIELAB color differences. CIELAB works well in specifying the color of an object, but color differences calculated with the formula have limited value for pass/fail decisions. These component color differences (dL, da, db ) are calculated by simply subtracting the L a b values for the standard from the L a b values for the trial. The dL, da, db values should indicate the direction of color difference from the standard (e.g., lighter or darker). They are commonly used to establish the allowable color limits from a standard. However, in applying these delta differences as limits for color acceptability, they should be adjusted for different colors. CIELAB, like Hunter L,a,b, is not a visually uniform color space. The limitations of CIELAB are not well understood throughout industry and the numbers continue to be applied without being adjusted for different colors and products. 

The L a b color space (also know as CIELAB) is presently the most popular color space for measuring object color and is used in many fields. In this color... 

There are other minor nonequivalencies of ISO test procedures compared to ASTM standards, but for color difference the ISO Test Procedure No. 105 is unique. Those who use Colour Measurement Committee (CMC) procedures—particularly CMC 2 1 Lightness to Color ratio—claim that it facilitates a uniform description for acceptability decisions that is better than any other system in existence. These equations permit the use of a single number tolerance, DEcmc, in a nearly uniform color space. The CMC formula is a modification to the perceptibility CIELAB formula. It is fully described elsewhere in this book, but it deserves some brief notice here because, after all, it is an ISO procedure. The CMC developed the basic British Standard No. 6923, Calculation of Small Color Differences. Soon afterward, in 1989, the American Association of Textile Chemists and Colorists (AATCC) adopted AATCC Test Method 173, CMC Calculation of Small Color Differences for Acceptability. Ford Motor Company indicated a preference for using CMC 2 1 ratio color difference for plastics weathering data for plastics interior trim materials. 

CIELAB An internationally accepted color space. CIE stands for Conjxnission Internationale de FEclairage. LAB stands for coordinates 1, a, and b, which are defined as mathematical coordinates in the three-dimensional color space. (Billmeyer, F. W. Saltzman, M. Principles of Color Technology , 2nd ed. Wiley New York, 1981 Chap. 2.)... 

D1N99, trying a different approach In contrast to the formulas stated above this formula tries to keep the calculation of the color difference as simple as in the CIELAB system while changing the color space to give a better conformance to the visual impression. 

The color transitions of series of indicators in the solvents discussed above have been described by the traditional 1931 CIE system x, y, Y) or by the latest color spaces CIELAB (L, a, b ), and CIELUV (L, u, v ), recommended by the CIE. 

Beside visual assessment, the color of an object can be characterized more precisely in terms of mathematical models, which are based on the remission and transmission spectra in the visible light area [6]. The most common CIELAB system, defines a color space and allows one to describe a specific color in terms of L (lightness) and the color coordinates a and b, and color differences or tolerances by related AL, A Ab and a combined AE value. L, a, b, values can be transformed into the probably more convenient terms of L (lightness), h (hue) and c (chroma). Today, colorimetry software is used for color matching and allows very precise calculations of pigment formulations. 

A commonly used and universally accepted system for describing color is the L a b color space, or CIELAB, developed by CIE, the International Commission on Illumination. The color space shown in Figure 111 is a three dimensional sphere comprised of three numerical coordinates ... 

Eq. 3-3), a concept introduced in Section 3.1.5 in the context of cluster analysis. This technique, introduced in 1976, uses the tristimulus values X, Y, and Z as inputs and converts these to the corresponding L, a, and b coordinates in the uniform color space. The distance between two points in the CIELAB system can be calculated as ... 

The values Xn, Yn, and Z are a reference white color and vary with the illumination selected. This color space also has some inherent distortion/ but far less than that of Figure 11.8. The CIELAB system is widely used in forensic analyses to describe color and color differences. 

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