1. A method performed by data processing apparatus, the method comprising: establishing a combination of color space component values weighted to generate skin-tone bias; converting color data associated with an image to skin-tone-biased luminance data in accordance with the established combination to generate a color-converted image; establishing a target region of the color-converted image that potentially contains at least a portion of a face; establishing an inset region inside the established target region, the inset region being sized to include a predetermined fraction of the target region; normalizing a luminance variance of the inset region to obtain a normalization scale; normalizing a luminance variance of the target region based on the obtained normalization scale; and detecting a face within the established target region using the established inset region.