An image processing circuit for multi-illumination white balance with thumbnail processing. The image processing circuit determines a set of initial weights for a source pixel in a thumbnail image by determining component values for multiple color channels of the source pixel. The image processing circuit determines a set of weights for the source pixel in a weight map for the thumbnail image. Each weight in the set of weights is determined based on corresponding initial weights from the set of initial weights. Each weight in the set of weights represents an intensity level of a respective chrominance class of multiple chrominance classes for the source pixel. The image processing circuit applies the set of weights to values of the color channels of the source pixel to generate color component values of the color channels of a target pixel in a target thumbnail image.