A European 640 x 486 PtSi camera for infrared reflectography

In this contribution we describe and evaluate the AIM 640P camera for Infrared reflectography. It is demonstrated that infrared reflectograms with high resolution and low geometric distortion can be acquired with this 640 x 486 pixel computer controlled Platinum Silicide camera system. The on-board 14 bit Analogue-to-Digital converter captures IR images in 16,384 grey-scales, compared to 256 with normal 8 bit AD-converters. This accuracy makes it possible to utilise the complete dynamic range, without the influence of gain and offset parameters during the examination. An internal Stirling cooler cools the detector to 85K thus avoiding the use of liquid nitrogen. This new European digital IRR system was evaluated and compared to a conventional vidicon system. The image quality of both systems was quantified through the experimental determination of the Modulation Transfer Function (MTF) for which a new experimental method was developed. In addition several paintings were reexamined with teh PtSi system for comparative purposes. Results from thes comparative studies demonstrate that the AIM 640P provides sharper (higher resolution) digital reflectograms with substantially decreased image distortion and a higher dynamic range.