A method for processing digital image data is proposed wherein a step of processing digital image data comprises or realizes a sub-step of image improvement with respect to said digital image data which uses or which is based on a process of re-mapping together with a process of dithering. The converter also including a circuit adapted to turn on and off the at least one transistor. Squaraine nucleus, Nile Red nucleus, benzodioxazole nucleus, coumarin nucleus or aza coumarin nucleus dyes are disclosed that exhibit a fluorescence emission of at least about 575 nm.