1. A method for estimating illumination of an image captured by a digital system, the method comprising: computing, with the digital system, ground truth white balance gains for each training image of a plurality of training images; clustering, with the digital system, the training images into reference illumination classes based on the ground truth white balance gains; deriving, with the digital system, feature vectors for each training image in each reference illumination class; training, with the digital system, an illumination classifier based on the feature vectors, wherein classification parameters for each reference illumination class are determined; computing, with the digital system, a feature vector for the image; identifying, with the digital system, at least one best reference illumination class for the image from the reference illumination classes using the feature vector for the image, the illumination classifier, and the classification parameters corresponding to each reference illumination class; computing, with the digital system, information for further processing of the image based on the at least one best reference illumination class, wherein the information is at least one selected from a group consisting of color temperature and white balance gains; and performing, with the digital system, further processing on the image based on the information.