Blending-weight diffusion for image colourisation

An image colourisation method based on diffusion of colour-blending weights is presented. The authors propose to use reciprocal function for smoothness measurement to determine the priority order of colour propagation in image colourisation. The reciprocal measurement can improve the recent exponential-measurement-based propagation, which has a trend towards being greedy for smooth pixels, and is likely to cause wrong boundaries nearby the object juncture joining the grey levels without significant difference. In addition, the proposed method uses the blending-weight diffusion instead of the direct propagation of chrominance values. By doing so, it can respond quickly to the user demand for stroke editing. Experimental results show that compared with the exponential-measurement-based propagation, the proposed method filled colours more precisely in the positions representing real object surfaces, and saved 85.92% of computation time for adding a stroke and 98.60% for deleting a stroke, to an illustrative image. Compared with two conventional techniques which also implement-blending weights, this method can provide the blending weights for acceptable colourisation by using the economical strokes which positions are less constrained and which sizes are reduced.