Pigment-based recoloring of watercolor paintings

The color palette used by an artist when creating a painting is an important tool for expressing emotion, directing attention, and more. However, choosing a palette is an intricate task that requires considerable skill and experience. In this work, we introduce a new tool designed to allow artists to experiment with alternative color palettes for existing watercolor paintings. This could be useful for generating alternative renditions for an existing painting, or for aiding in the selection of a palette for a new painting, related to an existing one. Our tool first estimates the original pigment-based color palette used to create the painting, and then decomposes the painting into a collection of pigment channels, each corresponding to a single palette color. In both of these tasks, we employ a version of the Kubelka-Munk model, which predicts the reflectance of a given mixture of pigments. Each channel in the decomposition is a piecewise-smooth map that specifies the concentration of one of the colors in the palette across the image. Another estimated map specifies the total thickness of the pigments across the image. The mixture of these pigment channels, also according to the Kubelka-Munk model, reconstructs the original painting. The artist is then able to manipulate the individual palette colors, obtaining results by remixing the pigment channels at interactive rates.