KEYWORDS: Optical correlators, Binary data, Image filtering, Optical filters, Signal to noise ratio, Optical signal processing, Computer simulations, Systems modeling, Digital filtering, Digital imaging
Binary phase-only synthetic discriminant functions are constructed with a variation of the Jared and Ennis relaxation algorithm and their performance is evaluated on an optical correlator. The correlation responses required in the algorithm can be obtained numerically or experimentally, but the filters constructed by these two different methods are not the same. Reasons for these differences are considered and the usefulness of the resultant filters is investigated.
The speed at which one or more targets can be recognized in a time-sequencing rotation-invariant binary phase-only filter (BPOF) optical recognition system can be improved significantly by integrating sequential correlation responses and using the integrated peak responses as inputs to the same statistical correlation plane filter (CPF) used for individual sequential correlation responses. Since commercially available BPOFs can be written at very high frame rates (350 frames per second), more than 10 correlation responses can be integrated during the frame time of an output camera operating at video rates. Therefore, the use of of integrated rather than individual sequential correlation responses reduces the processing time by a factor of 10 or more if the same standard video rate camera is used at the correlation plane. This paper presents results obtained using a prototype time-integrating BPOF correlator to achieve near real-time rotation-invariant recognition of both single and multiple targets in a noisy and cluttered input scene.
Two cameras used as output transducers in a time-sequenced templet-matching optical correction system are compared. One camera, a charge-injection device (CID) camera, is equipped with an image intensifier, automatic gain control (AGC), and a standard video output, while the second camera is a charge-coupled device (CCD) camera without an intensifier or AGC but with a computer interface custom-designed to use the camera's digital output. The cameras are used at the output of the optical correlator in order to integrate high frame-rate time-sequenced output correlation responses derived from binary phase-only filters. It is concluded that an image intensifier is the most important feature to have in a CCD or CID camera because the use of it results in a shorter integration time.
With the advent of high speed spatial light modulators, it is possible to write binary phase-only filters (BPOFs) faster than standard video rates. However, an optical correlation system which uses a camera operating at standard video rates to capture output correlation responses is limited to a maximum filter rate of 60 Hertz. This paper examines the use of a charge injection device (CID) camera to speed up the processing time of a BPOF-based rotation-invariant optical correlation system. Having integrating capabilities, the CID camera can integrate several output correlation plane responses during the frame time of the camera. In this paper, the performance of an integrating correlator is presented. The influence of factors such as the input image noise density, the number of integrated correlation responses, and the size of ternary low-frequency blocks on correlation responses are explored.
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