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Frame skipping in low bit video coding could significantly reduce the visual quality of reconstructed video. At the same time, if the complexity of the video sequence remains high for a long period, then driving up the long term average bit rate, the only resort of MPEG-4 Q2 rate control algorithm results in using a high quantization scale, which shows a poor visual quality of the reconstructed video. This paper analyzes the main causes of frame skipping in current MPEG-4 frame rate control scheme, and presents a new rate control algorithm based on the quadratic R-D model over a CBR channel. Key features of the present work are. 1) the bits allocated to each P-frame or B-frame are in proportion to its distance from the end of this GOP, i.e. more bits are allocated to the frames that are nearer to their reference Ⅰ -frame: 2) the target buffer level is changeable in the GOP, at the end of each GOP( five P-frames or B-frames), the target buffer level is linearly reduced from 1/2 to 1/4 of buffer size, to other frames, the target buffer level is set to 1/2 of buffer size: 3 ) a selective and judicious use of the reduced resolution mode, in addition to a modulation of the quantization scale parameter, is to control the average long term bit rate. Experimental results with different video sequences of varied complexity, encoded at low bit rates show better efficacy of the proposed algorithm than MPEG-4 Q2 rate control scheme, and the experimental results also show that the improved algorithm has significantly reduced the number of frame skipping, increased the overall PSNR, and improved the perceptual quality. 相似文献
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根据人的视觉规律,白天可看到各种景物的五颜六色和丰富的细节变化,而到了夜晚由于人眼对夜暗分辩率较低,所看到的景物几乎都成了灰色。为此,在拍摄过程中必须针对夜晚的"景色"特征,准确把握拍摄的色彩基调,从而使人们观看时在视觉和心里上的感受与夜间事件现场的情绪和气氛相吻合,犹如身临其境。一、准确选定夜间的色彩基调,提高电视画面的艺术感染力把握好夜间拍摄的色彩,首先应选定景象的基本色 相似文献
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CCD是数码相机最为核心的部件,其功能是把透过镜头的光线捕获并转换为电子信号。由CCD的性能来决定数码影像的质量的因素主要有:CCD尺寸、像素数、单位像素大小、文件传输和读出方式、CCD虑镜颜色。 相似文献
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为了把具有线性相位的IIR滤波器通过给合构成多通道非均匀最大抽取滤波器组,可以将综合滤波器与相应的分析滤波器取为相似,用他们之间的适当的同相与反相关系抵消抽取时产生的混叠,而对组合延时特性则采用最小平方误差和Remez算法优化逼近一个恒定数值,可使所得设计结果近似实现完全重构。IIR滤波器可采用具有近似线性相位的通用参数滤波器。 相似文献
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