Digital video quality vision models and metrics phần 6

Những tính năng này đã được lựa chọn theo kinh nghiệm từ một số ứng cử viên để mang lại sự tương quan tốt nhất với dữ liệu chủ quan. Đầu tiên, ngang và thẳng đứng cạnh các bộ lọc nâng cao được áp dụng để tạo điều kiện tính toán gradient trong giai đoạn khai thác tính năng. | MODELS AND METRICS as inputs. After their conversion to the appropriate perceptual color space each of the resulting three components is subjected to a spatio-temporal filter bank decomposition yielding a number of perceptual channels. They are weighted according to contrast sensitivity data and subsequently undergo contrast gain control for pattern masking. Finally the sensor differences are combined into a distortion measure. Color Space Conversion The color spaces used in many standards for coding visual information . PAL NTSC JPEG or MPEG already take into account certain properties of the human visual system by coding nonlinear color difference components instead of linear RGB color primaries. Digital video is usually coded in Y C B CR space where Y encodes luminance CB the difference between the blue primary and luminance and CR the difference between the red primary and luminance. The PDM on the other hand relies on the theory of opponent colors for color processing which states that the color information received by the cones is encoded as white-black red-green and blue-yellow color difference signals see section . Conversion from Y CBCR to opponent color space requires a series of transformations as illustrated in Figure . Y CBCR color space is defined in Figure Color space conversion from component video Y C B CR to opponent color space. ITU-R Rec. . Using 8 bits for each component Y is coded with an offset of 16 and an amplitude range of 219 while CB and CR are coded with an offset of 128 and an amplitude range of 112. The extremes of the coding range are reserved for synchronization and signal processing headroom which requires clipping prior to conversion. Nonlinear R G B values in the range 0 1 are then computed from 8-bit Y CBCR as follows Poynton 1996 R0 G0 B0 219 1 0 0 Y0 16 . CB - 128 C0 CR 128 1 1 1 PERCEPTUAL DISTORTION METRIC 85 Each of the resulting three components undergoes a .