Disclosed herein is a method and system for determining a billing structure for outputting documents using an image processing apparatus. If image data of the document includes color pixels, a billing structure is determined based on an estimated total color pixel count. The color pixels of the image data are counted in a device independent space and the total color pixel count of the image data to be output in a device dependent space is estimated. Based on the estimation, a billing structure is chosen. Processing and determining a billing structure based on image data in the device independent space avoids charging a customer for color print job when only a small amount of color pixels are printed. It also encourages determining charges independently of the marking engine or output device.