introducing capacity surface to estimate watermarking capacity

one of the most important parameters in evaluating a watermarking algorithm is its capacity. generally, watermarking capacity is expressed by bits per pixel (bpp) unit measure. but this measure does not show what the side effects would be on image quality, watermark robustness and capacity. in this paper we propose a three dimensional measure named capacity surface which shows the effects of capacity on visual quality and robustness. by this measure we can objectively find the amount of degradation and robustness for different capacities. our experimental results are compatible with the previous related works in this field (about 20% tolerance) while provide more flexibility for capacity estimation in different conditions.