K.M. Lam, Metamerism and colour constancy,Ph.D. thesis, University of Bradford, 1985.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....Quantities R; G; B; and R; G; B; are computed from the tristimulus values of the first and second illuminants, respectively, by multiplying the corresponding XYZ vectors by Mc z. The currently most popular chromatic adaptation transforms are the von Kries CAT [12] the linearized Bradford CAT [13,14], the Sharp CAT [15] and the CMCCAT2000 transform [16] All are based on the von Kries model as described in equation (8) but they apply the white point scaling to different RGB sensors (see Figure 6) i.e. they use different transformation matrices MC T. Recent studies [17] have shown that for ....

....statistically significantly different from CMCCAT2000 at 95 percent confidence. To evaluate if the resulting RGB sensors have good chromatic adaptation transform behavior, Lam s corresponding color data set [18] was used, which was also employed to derive both the Bradford and the Sharp CATs [13,15]. Lam had observers predict the appearance of 58 wool samples under illuminants A and D65. The resulting corresponding color data set has been used extensively to test chromatic adaptation transforms and has been found to be quite stable [16] The Mc T transforms found through the spherical ....

K.M. Lam, "Metamerism and Colour Constancy," Ph.D. Thesis, University of Bradford, 1985.

....for psycho visually derived constant hue data [10] in a log RGB opponent color space. Using this definition of hue constancy, we also calculate the hue behavior of a number of sensors found in the color science and imaging community, such as ROMM [7] ITUBT. R 709 [11] LMS, Sharp [12] Bradford [13], and color ratio stable sensors [14] The hue definition of the log RGB opponent color space is similar to the hue definitions in other color spaces (see part 2) It has been successfully applied to image retrieval applications [8] It is gamma invariant, i.e. the power function usually applied ....

....ROMM sensors. The mean residual error is equal to O. 1686. Figure 7: Hue constancy for the Sharp sensors [12] The mean residual error is equal to 0.1504. Figure 5. Hue constancy for the 709 sensors. The mean residual error is equal to 0.1653. Figure 8: Hue constancy for the Bradford sensors [13]. The mean residual error is equal to 0.1423. Figure 6. Hue constancy for the LMS sensors. The mean residual error is equal to 0.1039. Figure 9. Hue constancy for the sharp sensors that keep color ratios most stable over different illuminants [14] The mean residual error is equal to ....

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K.M. Lam, "Metamerism and Colour Constancy," Ph.D. Thesis, University of Bradford, 1985.

....the corresponding XYZ vectors by Mc T. The currently most popular chromatic adaptation transforms are the von Kries CAT operating on cone responses, derived by the Hunt Pointer Estevez (HPE) linear transform from XYZ color matching functions to relative LMS [11] the linearized Bradford CAT [12,13]; the Sharp CAT [14] and the CMCCAT2000 transform [9] All are based on the von Kries model as described in equation (1) but they apply the white point scaling to different RGB sensors (see Figure 1) i.e. they use different transformation matrices MCA T. CMCCAT2000 has been developed to ....

....scaling to different RGB sensors (see Figure 1) i.e. they use different transformation matrices MCA T. CMCCAT2000 has been developed to supersede CMCCAT97. CMCCAT97 is a chromatic adaptation transform included in the CIECAM97s color appearance model. It is based on the Bradford transform [12], but includes a step to model partial adaptation [15] CMCCAT2000 was developed by optimizing the transformation matrix MCA T SO that the perceptual error of predicted and actual corresponding colors for a number of corresponding color data sets [16] is minimized. The nonlinear correction in the ....

K.M. Lam, Metamerism and Colour Constancy, Ph.D. Thesis, University of Bradford, 1985.

....the data set and color difference metric used. The sharp transform performs equally well as the linearized Bradford transform: there is no statistically significant difference in performance for most data sets. 1. Lam s Experiment In his experiment to derive a chromatic adaptation transform, Lam [1] used 58 dyed wool samples. His main objectives when choosing the colors were that the samples represent a reasonable gamut of chromaticities corresponding to ordinary collections of object colors (see Figure 1) and that the samples have various degrees of color constancy with regard to change of ....

....the sharp and the linearized Bradford transform (Tables 5, 6, and 7) the sharp transform performs either equally well, or better for 2 or 3 out of the 16 data sets, depending on the color difference metric used. Table 1: Characteristics of the corresponding color data sets used in this study [1, 3, 15, 16, 17, 18, 19]. Approx. Illuminant Data Set No. of Samples Test Ref. Sample Size Medium Experimental Method Lam 58 D65 A L Refl. Memory Helson 59 D65 A S Refl. Memory CSAJ 87 D65 A S Refl. Haploscopic Lutchi 43 D65 A S Refl. Magnitude Lutchi D50 44 D65 D50 S Refl. Magnitude Lutchi WF 41 D65 WF S ....

K.M. Lam, "Metamerism and Colour Constancy," Ph.D. Thesis, University of Bradford, 1985.

....Chromatic Adaptation Transform (BFD CAT) A widely used newer chromatic adaptation transform is the Bradford transform. It was empirically derived by Lam from a set of corresponding colors as determined from 58 dyed wool samples with varying color constancy, evaluated under illuminants A and D65 [5]. Because of the varying color constancy of the samples, the experiment was designed so that corresponding colors represented the same appearance under the different illumination sources, and not necessarily the same sample. The original Bradford chromatic adaptation transform is a modified ....

....finding the transform that minimizes the perceptual mapping errors. Luo and Hunt have accumulated several such sets from the literature for the purpose of deriving and evaluating color appearance models and chromatic adaptation transforms [10] They include data sets based on reflective stimuli [5, 11 14], and data sets based on monitor and projected stimuli [15, 16] The characteristics of the 16 corresponding color data sets used for the performance comparison are summarized in Table 1. Table 1: Characteristics of the corresponding color data sets used in this study. Approx. Illuminant Data ....

K.M. Lam, "Metamerism and Colour Constancy," Ph.D. Thesis, University of Bradford, 1985.

.... Sabine Ssstrunk (1, 2) 1) School of Information Systems The University of East Anglia Norwich NR4 7TJ (2) Communication Systems Department Swiss Federal Institute of Technology (EPFL) Lausanne, Switzerland Abstract The Bradford chromatic adaptation transform, empirically derived by Lam [1], models illumination change. Specifically, it provides a means of mapping XYZs under a reference source to XYZs for a target light such that the corresponding XYZs produce the same perceived colour. One implication of the Bradford chromatic adaptation transform is that colour correction for ....

K.M. Lam, "Metamerism and Colour Constancy, " Ph.D. Thesis, University of Bradford, 1985.

....FS FL FC Average surround (20 Y b=100) 3.0 1.0 1.00 Dim surround (1 Y b=100 20) 3.5 1.0 1.15 Dark surround (Y b=100 1) 4.2 1.0 0.95 TABLE I Table 1: Values of parameters FS , FL and FC The use of the LLAB space needs two steps. The rst one is a BFD chromatic adaptation transform [41]. It is used to convert tristimulus values X s Y s Z s of the surface under any source illuminant to tristimulus values X r Y r Z r under the reference illuminant D6500. The second step is a computation, modi ed with regard to the color space CIELab1976 color space, of the following perceived ....

K. M. Lam, Metamerism and colour constancy, Ph.D. thesis, University of Bradford, 1985.

....is valid for comparing colors in a complex scene. Second, sensitivity to color differences depends on the color of the background or adaptation state of the eye, which can be changed by ambient illumination. To this end, a variety of Chromatic Adaptation Transforms (CAT) have been developed [7, 8]. CATs take into account the ability of the eye to adapt to the spectral content of the illumination in the scene. In the case of digital color cameras, the image processing firmware in the cameras generally have white balance modules incorporated in them for this purpose [9] In the development ....

K.M. Lam, Metamerism and colour constancy, Ph.D. thesis, University of Bradford, 1985.

....of what is currently available. Various aspects of the model can be traced to work of (in alphabetical order) Bartleson, Breneman, Fairchild, Estevez, Hunt, Lam, Luo, Nayatani, Rigg, Seim, and Valberg among others. Examples of these contributions include the Bradford chromatic adaptation transform (Lam, 1985; Luo, 1997) a different exponent on the short wavelength response (Nayatani et al. 1982) partial adaptation factors (Fairchild, 1996; Nayatani, 1997) cone responsivities (Estevez; see Hunt and Pointer, 1985) a hyperbolic response function (Seim and Valberg, 1986) redness greenness and ....

Lam, K.M., (1985), Metamerism and colour constancy, Ph.D. Thesis, University of Bradford.

....as a matrix transform of the colour matching functions, and appear to be sharpened : they are sensitive to smaller bands of the visible spectrum. Yet, Bradford sensors were not derived using spectral sharpening. Rather, they were the result of fitting psychophysical corresponding colour data [2]. In this paper, we use spectral sharpening to investigate Bradford sensors. Our first result is to show that there exist three intervals of the visible spectrum with respect to which spectral sharpening delivers sensitivity curves which are close to the Bradford sensors. We observe, however, that ....

K.M. Lam. Metamerism and colour constancy. PhD thesis, University of Bradford, 1995.

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K.M. Lam, Metamerism and colour constancy,Ph.D. thesis, University of Bradford, 1985.

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K. M. Lam, "Metamerism and colour constancy," Ph.D. Thesis, University of Bradford, 1985.

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K.M. Lam, "Metamerism and Colour Constancy," University of Bradford (1985)

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