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This paper presents a low-power encoding technique, called chromatic encoding, for the digital visual interface standard (DVI), a digital serial video interface. Chromatic encoding reduces power consumption by minimizing the transition counts on the DVI. This technique relies on the notion of tonal locality, i.e., the observation - first made in this paper - that the signal differences between adjacent pixels in images follow a Gaussian distribution. Based on this observation, an optimal code assignment is performed to minimize the transition counts. Furthermore, the three-color channels of the DVI may be reciprocally encoded to achieve even more power saving. The idea is that given the signal values from the three-color channels, one or two of these channels are encoded by reciprocal differences with a number of redundant bits used to indicate the selection. The channel selection problem is formulated as a minimum spanning tree problem and solved accordingly. The proposed technique requires only three redundant bits for each 24-bit pixel. Experimental results show up to a 75% power reduction in the DVI.