1. A method of automatically controlling focus of a camera comprising: characterizing an image sensor included in the camera by obtaining a plurality of images of a color testing target in controlled illumination conditions, comprising: obtaining a set of values in a color space based on a response by the image sensor to a corresponding one of a plurality of color testing targets, each of the plurality of color testing targets having a different reflectance spectrum; obtaining a set of values based on a correlation between a reflectance spectrum of a training surface and a combination of reflectance spectra of the plurality of color testing targets; and based on the correlation, obtaining a predicted response of the image sensor to the training surface; obtaining an image scene with the image sensor included in the camera; identifying one or more regions of the image scene including skin tone pixels by using the characterization of the image sensor; and automatically controlling focus of the camera based on the identified one or more regions.