A new frequency processing algorithm based on multi-resolution analysis
Daisuke Kaji, Chieko Sato, Akiko Kano, Hisanori Tsuchino · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2003
The purpose of this study was to develop a new frequency processing algorithm based on multiresolution analysis, a common method of signal analysis, and thus to improve the diagnostic image quality of digital x-ray imaging systems such as computed radiography (CR). The newly developed algorithm, termed 'hybrid processing', has three unique features. First, the original image is decomposed into plural frequency bands, and each frequency component is weighted and added back to the original image. Second, at the decomposition stage, rather than employ a conventional simple averaging filter, a binomial filter is used to create unsharp images. Third, an enhancement characteristic is established for each unsharp image based on a smooth compensation function predetermined by the density and contrast of the unsharp image. Hybrid processing was applied to approximately 500 clinical CR images, including images of the chest, abdomen, and extremities. Image decomposition, and the weighting and re-addition of its frequency components produced optimal renditions from low through high frequencies. Further, the binomial filter provided smooth frequency response with a reasonably short processing time. Combined with the enhancement characteristic established for each unsharp image, the binomial filter effectively reduced unfavorable noise enhancement and such artifacts as overshoot and undershoot.