This paper presents an overview of the transform and quantization designs in H.264. Unlike the popular 8 8 discrete cosine transform used in previous standards, the 4 4 transforms in H.264 can be computed exactly in integer arithmetic, thus avoiding inverse transform mismatch problems. The new transforms can also be computed without multiplications, just additions and shifts, in 16-bit arithmetic, thus minimizing computational complexity, especially for low-end processors. By using short tables, the new quantization formulas use multiplications but avoid divisions.

Figure 1: Image reproduced adaptively for low ambient light (dark room scenario -left) and high ambient light (sunlight scenario -right). The display adaptive tone mapping can account for screen reflections when generating images that optimize visible contrast. AbstractWe propose a tone mapping operator that can minimize visible contrast distortions for a range of output devices, ranging from e-paper to HDR displays. The operator weights contrast distortions according to their visibility predicted by the model of the human visual system. The distortions are minimized given a display model that enforces constraints on the solution. We show that the problem can be solved very efficiently by employing higher order image statistics and quadratic programming. Our tone mapping technique can adjust image or video content for optimum contrast visibility taking into account ambient illumination and display characteristics. We discuss the differences between our method and previous approaches to the tone mapping problem.

We propose a tone mapping operator that can minimize visible contrast distortions for a range of output devices, ranging from e-paper to HDR displays. The operator weights contrast distortions according to their visibility predicted by the model of the human visual system. The distortions are minimized given a display model that enforces constraints on the solution. We show that the problem can be solved very efficiently by employing higher order image statistics and quadratic programming. Our tone mapping technique can adjust image or video content for optimum contrast visibility taking into account ambient illumination and display characteristics. We discuss the differences between our method and previous approaches to the tone mapping problem.

Backlight dimming is a dominant method for power reduction in LCDs. Image processing with a simple boost and clip can compensate for such dimming-restoring image brightness. We propose a low complexity approach which replaces hard clipping with smooth roll-off to reduce clipping artifacts. An additional high-quality approach uses a two-channel spatial-frequency decomposition to preserve highlight detail attenuated by the roll-off. Image quality is improved and power savings can be increased by more-aggressive backlight dimming. FIGURE 3 -Tone-scale backlight compensation.FIGURE 5 -Two-channel BP block diagram.FIGURE 4 -Two MFP tone scales.

In this paper, we investigate how to adapt different parameters in H.263 source coding, transport processing and error concealment to optimize end-to-end video quality at different bitrates and packet loss rates for H.323-based packet video. First, different intra coding patterns are compared and we show that the contiguous rectangle or square block pattern offers the best performance in terms of video quality in the presence of packet loss. Second, the optimal intra coding frequency is found for different bitrates and packet loss rates. The optimal number of GOB headers to be inserted in the source coding is then determined. The effect of transport processing strategies such as packetization and retransmission is also examined. For packetization, the impact ofpacket size and the effect ofmacroblock segmentation to picture quality are investigated. Finally, we show that the dejitter buffering delay can be used to the advantage for packet loss recovery with video retransmission without incurring any extra delay.