Mobile Receiver Design Increases The Resolution
When compressing a video sequence, modern techniques achieve high compression ratios by removing image details (high-frequency information), producing a degradation of the decoded image. This degradation is negligible for high bit rates but can result in unbearable quality where bit rates are very low and compression ratios must therefore be high. Sometimes the lost information can be recovered from frames that occur shortly before or after the one that is degraded. This is known as super-resolution (SR) but its high computational load usually prevents real-time implementation of the process. Moreover, such algorithms are designed in such a way that a feasible implementation would require a huge re-design effort.
Although several algorithms for SR have been proposed (a comprehensive classification is provided by Borman1), all lack a practicable real-time implementation: for those who know the field, this even includes the Segall2 and Gunturk3 compression environments. Here, we jointly consider the algorithm specification and the system design as a whole process, where the restrictions imposed by the platform are taken into account by the algorithm from the first design steps. Our aim is to contribute towards research in low-cost and high-performance multimedia devices. To this end, we propose a mobile system for real-time video reception over the Digital Audio Broadcast4 (DAB) network, using programmable logic devices (PLDs) with embedded microprocessors as the target technology. As the data rate of DAB is limited to 1.8432Mbs?1, the bandwidth of the encoded sequence must be drastically reduced, decreasing the quality due to compression losses.
The system works with a typical ITU-R 601 (750??576 pixels) video signal, as can be seen in Figure 1. The sequence is pre-processed to get QCIF (Quarter Common Interface Format, designed for teleconferencing) frame size (176??144 pixels) and to extract some image characteristics that will keep important information for the XSR process. The down-sampled sequence is encoded using the MPEG-4 standard, delivering a reduced bandwidth bitstream. Next, a MPEG-2 transport stream (TS) is generated to be transmitted over IP (internet protocol) tunnelling through the DAB network. Alternately, and for testing purposes, the IP datagrams can be coded in the receiver data interface (RDI) and transmitted through an optical link (IEC-958). On reception, the user selects the channel identifier, which enables the data containing the MPEG-4 bitstream to be decoded. After decoding, an XSR process increases the resolution to CIF (352??288 pixels) size, where a LCD-display is used for visualization.