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A von Orelli

Publications and source records attributed to A von Orelli.

3 recordsLinked to original sources
PubMed1999

High-definition true-colour television for use in minimally invasive medical procedures.

Endoscopes are key elements in the application of minimally invasive medical procedures. Thereby, image quality, ease of application and safety are of decisive importance for the user. This communication is primarily concerned with aspects relating to image quality. Standard television technology is presently used in endoscopes for image presentation purposes. It is however shown, that the inherent optical quality of most endoscopes exceeds the performance of standard TV. Accordingly, a special purpose advanced digital television system exhibiting true colour performance has been developed. Since endoscopic images usually are circular, its aspect ratio is quadratic with a spatial resolution of 1000 x 1000 pixels. It has furthermore a temporal resolution of 1 to 30 Hz noninterlaced and a contrast resolution of 56.6 dB. The design and performance of the system is documented.

Endoscopes↗
PubMedDate not supplied

Passive autofocusing for digital endoscopic imaging systems.

An autofocus is a desirable feature of an endoscope, because it relieves the user from performing a task which can be automated and thereby prevents unnecessary interruptions in the work to be performed. Autofocusing is in general best achieved by an active system, i.e., on the basis of a distance measurement. Yet, in handheld medical endoscopes such a method is unsuited because of the added weight associated with the necessary electromechanical components. Autofocusing should rather be performed passively, furthermore, in applications which are particularly critical with respect to safety, e.g., in the eye, a stable and reliable operation in real time and without interruption is necessary. Passive autofocus strategies applied to date and known to the authors lead however to algorithms which are either too slow for a real time implementation and/or are influenced by the structure of the object which is to be brought into focus. Accordingly, a new autofocus procedure has been developed which exhibits a stable and reliable operation in real time under all circumstances of interest. It is based on the squared differences of the intensity of adjacent points in both dimensions of a plane image (Square Plane Sum Modulus Difference, SPSMD) and as such particularly suitable for digital camera systems and real-time needs (typically, 30 evaluations per second on an image of 1024 x 1024 pixels). The SPSMD criterion is more sensitive, has a larger SNR than other focus criteria known to the authors and exhibits in particular no secondary extrema which could adversely affect proper focusing. As it includes intensity differences in both (perpendicular) directions in the image plane, it is essentially independent of image structures.

Endoscopes↗