1. A processor-implemented method for processing image data using an image processing apparatus, the image processing apparatus comprising at least one processor for processing documents containing image data comprising a plurality of pixels, the method comprising the following acts implemented by the at least one processor: receiving image data of a document comprising a plurality of pixels; determining a billable count of color pixels in the received image data by: determining a first count of color pixels in the image data in device independent space by applying a neutral page determination algorithm to the received image data, the determined first count comprising counting at least a number of true color pixels and fuzzy color pixels in the received image data; converting the plurality of pixels of the image data into device dependent space; determining a second count of color pixels for marking in the device dependent image data; transforming the determined first and second counts of color pixels, and determining a minimum of the two transformed pixel counts, wherein the determining of the billable count of color pixels further comprises: comparing the number of true color pixels from the applied neutral page determination algorithm to a predetermined threshold, and, if the comparison is greater, the transforming comprising applying a first transformation using the number of true color pixels therein, and using this first transformation result in the minimum calculation, and determining the minimum using the first transformation result, else, the transforming comprising applying a second transformation without using of the number of true color pixels, and using this second transformation result in the minimum calculation, and determining the minimum using the second transformation result.