On-Line Interactivte Computer Processing of Acoustic Images
An interactive on-line computer image processing system designed for use in acoustic image restoration and enhancement has been developed. Signals from a Bragg-diffraction ultrasonic imager have been accessed on-line by a minicomputer and digitized. Signal and noise can be measured quantitatively, and digital restoration and enhancement techniques can be employed to minimize the effects of the different kinds of noise which influence image quality.
Systematic noise has been removed by employing two different approaches: 1) band rejection filtering and 2) subtractive background compensation. Results of their relative performance will be presented in this paper. Much of this noise is time-invariant and stems from the background insonification of the sound veil. Because of its time-invariant nature, time averaging is of little or no value, as has been shown in experiment.
Speckle noise, which is present in all coherent imaging systems, has been effectively reduced by neighborhood averaging. A similar type of interference phenomenon, also common to all coherent imaging systems, is known as “ringing” and has been studied using this system. Ringing, due to sharp cutoffs in the spatial frequency domain of the images, has been significantly reduced by using windowing techniques.
KeywordsSpatial Frequency Systematic Noise Acoustic Image Aluminum Block Neighborhood Average
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