Decomposing Time-lapse Paintings into Layers

The creation of a painting, in the physical world or digitally, is a process that occurs over time. Later strokes cover earlier strokes, and strokes painted at a similar time are likely to be part of the same object. In the final painting, this temporal history is lost, and a static arrangement of color is all that remains. The rich literature for interacting with image editing history cannot be used. To enable these interactions, we present a set of techniques to decompose a time lapse video of a painting (defined generally to include pencils, markers, etc.) into a sequence of translucent "stroke" images. We present translucency-maximizing solutions for recovering physical (Kubelka and Munk layering) or digital (Porter and Duff "over" blending operation) paint parameters from before/after image pairs. We also present a pipeline for processing real-world videos of paintings capable of handling long-term occlusions, such as the painter's hand and its shadow, color shifts, and noise.