Automatic white balance of captured images can be performed based on a gray world assumption. One aspect relates to an apparatus comprising a collection module and a processor. The collection module is configured to accumulate (a) red/green and blue/green color ratio values of a plurality of pixels in a captured image for each cluster of a plurality of clusters and (b) a number of pixels having red/green and blue/green color ratios associated with each cluster, the clusters comprising daylight, fluorescent, incandescent, and a outdoor green zone. The processor is configured to determine which cluster has a highest accumulated number of pixels, and use the cluster with the highest accumulated number of pixels to perform white balancing for the captured image.