Automatic correction of exposure problems in photo printer

In this paper we consider a problem of automatic enhancement of amateur photos in photo printer. The purpose of correction consists of making photos more pleasant for an observer. The photos with various exposure problems and with poorly distinguishable details in shadow areas are analyzed. Our approach is based on contrast stretching and alpha-blending of both brightness of the initial image and estimations of reflectance. For obtaining reflectance estimation a simplified illumination model is used. The luminance is estimated using bilateral filter. Reflectance is estimated using heuristic functions of ratio between brightness of the initial image and estimation of luminance. The correction parameters are chosen adoptively based on histogram analysis. Noise suppression and some sharpening occur during correction. The time and memory optimization issues are considered. Look-up tables and recursive separable bilateral filter are applied to speed up the algorithm. The quality of the algorithm is evaluated by surveying of observer's opinions and by comparisons with already existing software and hardware solutions for local shadow correction. The proposed algorithm was implemented into firmware of Samsung dye-sublimation compact photo printer.