1. A method of re-identifying an object in a test image, the method comprising the steps of: a computer determining brightness transfer functions (BTFs) between respective pairs of training images captured by first and second cameras; the computer determining respective measures of similarity between the first test image and each of the training images captured by the first camera; based on the measures of similarity, the computer determining weights of the training images captured by the first camera, the weights corresponding to the BTFs; the computer determining a weighted brightness transfer function (WBTF) by weighting the BTFs by the corresponding weights and combining the weighted BTFs; based on the WBTF, the computer transforming the first test image to better match one of the training images captured by the second camera; the computer identifying another test image, captured by the second camera, that is closer in appearance to the transformed test image than other test images captured by the second camera; and the computer designating an object in the identified test image as a re-identification of the object in the first test image.