Colorization of Freehand Line Drawings Using Reference Images

Abstract

We present a colorization method for freehand line drawings. The proposed method is implemented on a tablet PC and the system displays a photograph with low contrast on a drawing area as a reference image. As the user sketches a scene, the system paints it with colors in the reference image. Colorization is accomplished by Delaunay triangulation for the set of sampling points on the sketch lines, calculating an average color in each triangle on the reference image, and filling the color in each triangle. As the above naive procedure makes a mosaic image, we lastly apply smoothing of color between neighboring triangles whose shared side is not laid on any sketch line.