  Compared to color images captured by conventional RGB cameras, monochrome
images usually have better signal-to-noise ratio (SNR) and richer textures due
to its higher quantum efficiency. It is thus natural to apply a mono-color
dual-camera system to restore color images with higher visual quality. In this
paper, we propose a mono-color image enhancement algorithm that colorizes the
monochrome image with the color one. Based on the assumption that adjacent
structures with similar luminance values are likely to have similar colors, we
first perform dense scribbling to assign colors to the monochrome pixels
through block matching. Two types of outliers, including occlusion and color
ambiguity, are detected and removed from the initial scribbles. We also
introduce a sampling strategy to accelerate the scribbling process. Then, the
dense scribbles are propagated to the entire image. To alleviate incorrect
color propagation in the regions that have no color hints at all, we generate
extra color seeds based on the existed scribbles to guide the propagation
process. Experimental results show that, our algorithm can efficiently restore
color images with higher SNR and richer details from the mono-color image
pairs, and achieves good performance in solving the color bleeding problem.
