Abstract
Acoustic holography is a transmissionโbased ultrasound imaging method that uses optical image reconstruction and provides a larger field of view than pulseโecho ultrasound imaging. A focus parameter controls the position of the focal plane along the optical axis, and the images obtained contain defocused content from objects not near the focal plane. Moreover, it is not always possible to bring all objects of interest into simultaneous focus. In this article, digital image processing techniques are presented to (1) identify a โbest focusedโ image from a sequence of images taken with different focus settings and (2) simultaneously focus every pixel in the image through fusion of pixels from different frames in the sequence. Experiments show that the threeโdimensional image information provided by acoustic holography requires positionโdependent filtering for the enhancement step. It is found that filtering in the spatial domain is more computationally efficient than in the frequency domain. In addition, spatial domain processing gives the best performance. ยฉ 2002 Wiley Periodicals, Inc. Int J Imaging Syst Technol 12, 101โ111, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.10017