tailieunhanh - Digital video quality vision models and metrics phần 3

Cuối cùng, Chương 7 kết luận cuốn sách với một triển vọng phát triển đầy hứa hẹn trong lĩnh vực đánh giá chất lượng video. Tầm nhìn Thấy là tin nhìn là quan trọng nhất của các giác quan của chúng ta | Figure Approximations of achromatic a and chromatic b spatio-temporal contrast sensitivity functions Kelly 1979b Burbeck and Kelly 1980 Kelly 1983 . COLOR PERCEPTION 25 COLOR PERCEPTION In its most general form light can be described by its spectral power distribution. The human visual system however uses a much more compact representation of color which will be discussed in this section. Color Matching Color perception can be studied by the color-matching experiment Brainard 1995 . It is the foundation of color science and has many applications. In the color-matching experiment the observer views a bipartite field half of which is illuminated by a test light the other half by an additive mixture of a certain number of primary lights. The observer is asked to adjust the intensities of the primary lights to match the appearance of the test light. It is not a priori clear that it will be possible for the observer to make a match when the number of primaries is small. In general however observers are able to establish a match using only three primary lights. This is referred to as the trichromacy of human color vision. Trichromacy implies that there exist lights with different spectral power distributions that cannot be distinguished by a human observer. Such physically different lights that produce identical color appearance are called metamers. As was first established by Grassmann 1853 photopic color matching satisfies homogeneity and superposition and can thus be analyzed using linear systems theory. Assume the test light is known by N samples of its spectral distribution expressed as vector x. The color-matching experiment can then be described by t Cx where t is a three-dimensional vector whose coefficients are the intensities of the three primary lights found by the observer to visually match x. They are also referred to as the tristimulus coordinates of the test light. The rows of matrix C are made up of N samples of the so-called .

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