sản xuất bằng cách đi qua các tài liệu tham khảo qua một bộ lọc thấp qua thời gian. Một báo cáo về hiệu suất của các số liệu DVQ được đưa ra bởi Watson et al. (1999). Wolf và Pinson (1999) đã phát triển một thước đo chất lượng video (VQM) sử dụng thông tin tham khảo giảm trong các hình thức của các tính năng ở mức độ thấp được chiết xuất từ các khối không thơi gian của các trình tự. | 64 VIDEO QUALITY produced by passing the reference through a temporal low-pass filter. A report of the DVQ metric s performance is given by Watson et al. 1999 . Wolf and Pinson 1999 developed another video quality metric VQM that uses reduced reference information in the form of low-level features extracted from spatio-temporal blocks of the sequences. These features were selected empirically from a number of candidates so as to yield the best correlation with subjective data. First horizontal and vertical edge enhancement filters are applied to facilitate gradient computation in the feature extraction stage. The resulting sequences are divided into spatio-temporal blocks. A number of features measuring the amount and orientation of activity in each of these blocks are then computed from the spatial luminance gradient. To measure the distortion the features from the reference and the distorted sequence are compared using a process similar to masking. This metric was one of the best performers in the latest VQEG FR-TV Phase II evaluation see section . Finally Tan et al. 1998 presented a measurement tool for MPEG video quality. It first computes the perceptual impairment in each frame based on contrast sensitivity and masking with the help of spatial filtering and Sobel-operators respectively. Then the PSNR of the masked error signal is calculated and normalized. The interesting part of this metric is its second stage a cognitive emulator that simulates higher-level aspects of perception. This includes the delay and temporal smoothing effect of observer responses the nonlinear saturation of perceived quality and the asymmetric behavior with respect to quality changes from bad to good and vice versa. This metric is one of the few models targeted at measuring the temporally varying quality of video sequences. While it still requires the reference as input the cognitive emulator was shown to improve the predictions of subjective SSCQE MOS data. METRIC .
