Imaging geophysical data—taking the viewer into account

Abstract

AbstractA common way of presenting geophysical data from two‐dimensional sources is as a grey‐scale image. Some theoretical background to discrete image representation is described, and the deleterious effects of inappropriate (too sparse) sampling and display of such images discussed in an archaeological context. In high‐quality images, such as magazine illustrations or digital television, the sampling densities can be sufficiently high to avoid the appearance of artefacts. Geophysical images in contrast are often sampled at very low densities; if the effective area of each sample is significantly less than the sample spacing, then the classic effect called ‘aliasing’ in communication engineering, caused by the violation of Nyquist's criterion, will be seen. Knowledge of the sensor's footprint can be used to select an appropriate sample density, and so minimize this source of distortion. To maximize the visibility of what may be low‐contrast structures immersed in a high level of background noise, it is helpful also to consider the bandpass nature of the spatial frequency response of the human visual system. The non‐linear phenomenon of visual masking is shown to influence the choice on presentation methods. Copyright © 2004 John Wiley & Sons, Ltd.