Digital Airborne Camera by Rainer Sandau

Author:Rainer Sandau
Language: eng
Format: epub
Publisher: Springer Netherlands, Dordrecht

4.2.13 Ideal Optical Transfer Function

From the consideration of the physics of optical systems that led to the term “spatial bandwidth” product, we know that every optical system necessarily acts as a “spatial filter”, that is, it can only transmit an object of a specific size with a finite spatial bandwidth. This means that finer object details can only be transmitted with reduced contrast. There is a spatial frequency at which the contrast transmitted is so small that it is lost in the noise on the film or in the electronics. If a test image with known initial contrast is chosen as the object, this cut-off frequency is also given as a spatial “resolution” for this initial contrast.

Well corrected optical systems can be described as “linear” light intensity transfer systems and can therefore be characterised by a transfer function similar to electronics: this is called the OTF (Optical Transfer Function). The spatial intensity spectrum of our object, e.g. a city landscape, is then multiplied by the OTF for the optical system, resulting in the spectrum present at the sensor’s position. As the OTF has a cut-off frequency, the aerial image spectrum at the sensor, prior to its recording by the film or the CCDs, is already reduced in resolution and contrast. In principle, therefore, we lose information during imaging. The Fourier transform of the OTF is also called the “incoherent” point spread function that defines how blurred an object point appears on the sensor.

In the case of diffraction-limited imaging it is found that

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.