The handheld image processing device has a data receiver that is configured to receive reference encoded image data. The data includes a reference code value that is encoded by an external encoding system. The reference sign value represents a reference gray level, which is selected using a reference gray scale display function based on human visual perceptual non-linearities adapted to spatial frequencies at various light levels. Yes. The image processing device also includes a data converter configured to access a code mapping between the reference code value and the device specific code value of the image processing device. The device specific code value is configured to produce a gray level specific to the image processing device. Based on the code mapping, the data converter is configured to transcode the reference encoded image data into device specific image data encoded with the device specific code value.