To provide a device and method for improving perceptual nonlinearity-based image data exchange across different display capabilities.SOLUTION: A handheld image processor has a data receiver that is configured to receive reference encoded image data. The data includes reference code values, which are encoded by an external coding system. The reference code values represent reference gray levels, which are selected using a reference grayscale display function based on perceptual non-linearity of human vision adapted at different light levels to spatial frequencies. The image processor also has a data converter that is configured to access a code mapping between the reference code values and device-specific code values of the image processor. The device-specific code values are configured to produce gray levels that are specific to the image processor. Based on the code mapping, the data converter is configured to transcode the reference encoded image data into device-specific image data, which is encoded with the device-specific code values.SELECTED DRAWING: Figure 5