Multiresolution denoising of CCD thermal images for improved spatial temperature resolution

This paper deals with the enhancement of CCD- (charge-coupled device) based thermal images by applying multiresolution image denoising methods. The main focus of this experimental work lies in the attempt to determine and visualize the surface temperature of heated metal parts in the temperature range of approx. 300°C to 500°C. The aim is measurement of the temperature distribution of metallic objects at the lower physical limits of silicon based detectors at a very high spatial resolution. It is shown that the examined filter methods lead to an improved spatial temperature resolution (NETD, noise equivalent temperature difference) that is highly reproducible. A precondition for correct application of these denoising filters is an exact noise characterization of the imaging system. This noise characterization is based on the 'Photon Transfer Technique' which clearly demonstrates the Poisson characteristic to be the determining factor of the image formation process, i.e. the random nature of photon emission and detection is the dominant source of noise in the imaging system presented. Based on these results, examples for density and intensity estimates of Poisson noise images with multiresolution methods (wavelets, platelets) are presented, showing the improved image quality and temperature resolution after the denoising process.