Improvements to the triangulation range-sensing technique are described. The improvements greatly increase the range-data collection rate, while simultaneously providing for improved data integrity and a low-cost implementation. These benefits are achieved by using some unique abilities of the charge-injection-device image sensor. A laser-based investigation system has been built around a personal computer and used to evaluate the effectiveness of the improvements. Range data results are shown for the proposed application of printed-circuit board inspection.>

An investigation is conducted of the effects of various source statistics and buffer management algorithms for a buffer of fixed size, and an algorithm that provides particularly robust rate-distortion performance for a wide range of stationary sources is described. The performance of this scheme, which is referred to as the adaptive entropy-coded quantizer (AECQ), is compared to that of conventional adaptive pulse code modulation (APCM) operating at the same fixed channel transmission rate. Experimental results indicate that the AECQ can provide considerably improved performance and more robust operation than APCM. The relative sensitivity of the AECQ to scale mismatch is directly related to the rather simple memoryless feedback control strategy employed. This might be remedied by alternative choices of the memoryless feedback control function or by introducing memory. The former is much easier to implement and/or analyze than the latter.>

Buffer underflow and overflow problems associated with entropy coding are completely eliminated by effectively imposing reflecting walls at the buffer endpoints. Synchronous operation of the AECQ (adaptive entropy-coded quantizer) encoder and decoder is examined in detail, and it is shown that synchronous operation is easily achieved without side information. A method is developed to explicitly solve for the buffer-state probability distribution and the resulting average distortion when memoryless buffer-state feedback is used as well as when the source is stationary and memoryless. This method is then used as a tool in the design of low-distortion AECQ systems, with particular attention given to developing source scale-invariant distortion performance. It is shown that the introduction of reflecting buffer walls in a properly designed AECQ system results in a very small rate-distortion performance penalty and that the resulting AECQ system can be an extremely simple and effective solution to the stationary memoryless source-coding problem for a wide range of source types. Operation with nonstationary sources is also examined.>

The authors describe the theory and performance of a particular adaptive entropy-coded quantization (AECQ) scheme used in conjunction with 2-D DPCM (differential pulse code modulation) and operating on real-world image sources. The resulting system, called 2-D DPCM/AECQ, is described in detail and its performance illustrated on a typical real-world image. The system makes use of an adaptive buffer-control strategy to modify the DPCM quantizer characteristics on the basis of the buffer occupancy state. This adaptive buffer-state feedback is used to control the average rate of the variable-length entropy-coded quantizer code words at the input to the buffer, to allow interfacing to a fixed-rate transmission or storage channel. Image coding results demonstrate, both objectively and subjectively, that achievable performance is close to that predicted on the basis of rate-distortion considerations even for reasonably small buffer sizes.>