Aliasing and Reconstruction Distortion in Digital Intermediates

In this paper we address two types of artifacts associated with the image sampling and reconstruction process, namely, aliasing and reconstruction distortion. Aliasing is an artifact that results from sampling a continuous signal at too low a spatial rate relative to the input frequency content. Shannon's sampling theorem states that discrete sampling of a signal at a uniform rate higher than twice the highest frequency in the signal, called the Nyquist rate, will allow a perfect reconstruction of the original continuous signal. However, image displays do not reconstruct images according the ideal reconstruction equation, and in many cases, the display uses nothing more than a sample-and-hold reconstruction. It has long been known that non-ideal reconstruction can lead to distortion of the image data at frequencies below the Nyquist rate. Proper recognition of the distinction between aliasing and reconstruction errors can mean the difference between accepting and avoiding artifacts. With more and more film passing through the digital intermediate process, maintaining image quality is a high priority for artists and engineers alike. This paper discusses the causes of aliasing and reconstruction distortion and how to distinguish between them. We also discuss the implications for digital intermediate scanning and recording as well as the implications for digital cinema projection.

Published

2005-11

Content type

Original Research

DOI

10.5594/M00402

ISBN

978-1-61482-942-3