Takao Toi

A subband coding technique for image compression in single CCD cameras with Bayer color filter arrays

This paper presents a subband coding technique suitable for image compression in a single CCD camera with a Bayer color filter array (CFA). In it, we have applied a SSKF (symmetric short kernel filter) both horizontally and vertically to red and blue color signals, and a two dimensional perfect reconstruction filter to green color signals. Here, we compare this technique to two other image compression methods: DPCM and the Hadamard transform, each of which also allows an output signal from the CCD in a color camera to be compressed directly with simple logic circuitry and is suitable for use in low cost video conference cameras. Simulation results demonstrate that the subband coding offers the best quality (27-30 dB) with a compression ratio of approximately 2 bit/pel.

Stream applications on the dynamically reconfigurable processor

Dynamically reconfigurable processor (DRP) developed by NEC Electronics is a coarse grain reconfigurable processor that selects a data path from the on-chip repository of sixteen circuit configurations, or contexts, to implement different logic on one single DRP chip. Several stream applications have been implemented on the DRP-1, the first prototype chip, and evaluation results are presented. By pipelining the executions, DRP-1 outperformed Pentium III/4, embedded CPU MIPS64, and Texas Instruments DSP TMS320C67J3 in some stream application examples. We also present programming techniques applicable on dynamically reconfigurable processors and discuss their feasibility in boosting system performance.

Optimizing time and space multiplexed computation in a dynamically reconfigurable processor

One of the characteristics of our coarse-grained dynamically reconfigurable processor is that it uses the same operational resource for both control-intensive and dataintensive code segments. We maximize throughput from the knowledge of high-level synthesis under timing constraints. Because the optimal clock speeds for both code segments are different, a dynamic frequency control is introduced to shorten the total execution time. A state transition controller (STC) that handles the control step can change the clock speed for every cycle. For control-intensive code segments, the STC delay is shortened by a rollback mechanism, which looks ahead to the next control step and rolls back if a different control step is actually selected. For the data-intensive code segments, the delay is shortened by fully synchronized synthesis. Experimental results show that throughputs have increased from 18% to 56% with the combination of these optimizations. A chip was fabricated with our 40-nm low-power process technology.

High-level Synthesis Challenges for Mapping a Complete Program on a Dynamically Reconfigurable Processor

This paper presents a high-level synthesizer to map a complete program efficiently on a dynamically reconfigurable processor (DRP). Initially, we introduce our DRP architecture, which is suitable for control-intensive programs since it has a stand-alone finite state machine that switches “contexts” consisting of many processing elements (PEs). Then, we propose three new techniques optimized for our DRP. Firstly, we explain how synthesized control steps are mapped onto the contexts. Several control steps are combined as a context to utilize PEs efficiently since each control step does not require the same amount of operational units. Secondly, we describe a modulo scheduling algorithm for loop pipelining, considering both spatial and time dimensions of our DRP. Lastly, we explain a scheduling technique to optimize clock frequency, which can take advantage of multiplexer, wire and routing switch delays. We have demonstrated a JPEG-based image decoder example to evaluate our methods. Experimental results show that high area efficiency is achieved by balancing the number of PEs between contexts. Despite an overall increase in performance on pipelining of 3.6 times that without pipelining, the number of operational units increased by a factor of 2.2. The clock frequency is maximized with accurate delay estimation.

Color signal processing technique for single-chip CCD cameras that employ CPUs with SIMD instruction sets

This paper presents a color signal processing technique for use in single-chip CCD cameras that have CPUs employing SIMD (single instruction multiple data) instruction sets for signal processing. With it, the processing time can be reduced to a half that of conventional techniques. Color space conversion is performed before color interpolation, rather than after, and as a vector operation; this reduces the number of required multiply-operations to 3 or 4, depending on the number of colors being used, as opposed to 9 for conventional 3 by 3 matrix processing.