Light photon equalization and its application to X-ray film digitization.

The principle of light photon equalization (LPE) is to modulate the light source during X-ray film digitization so that the dynamic range of the transmitted light into a photo-detector can be precisely controlled to obtain improved signal-to-noise ratio (SNR). The modulation of the light source is derived from a smoothed image of the original digitized image. The final output digital image is reconstructed by convoluting the modulation function with the resultant LPE image. The LPE was implemented in a laser film digitizer as a prototype. The results shows that, although the dynamic range of X-ray films is about 10(4):1, the range of the transmission light into a photo detector was reduced to 10(2):1 with this technique. Also the SNR improved by a maximum factor of five in the lung area of a digitized chest radiograph.