What is disclosed is a decoding method for retrieving information bits encoded in a printed image comprising the steps of first receiving an input electronic image as a scanned version of the printed image. A region of interest in the image is then extracted and, for that region, an amount of K colorant present, denoted K.sub.H; is obtained. Further, a color value is generated therefrom and the GCR used for encoding that region is determined using K.sub.H and the obtained color value. Encoded information bits are retrieved therefrom based on the determined GCR. The estimated K.sub.H is preferably evaluated conditional to a capacity signal K.sub.L and a luminance signal L. From the obtained data, values of K.sub.H, K.sub.L, and L, are derived wherein K.sub.H is estimated from a high resolution scan, and K.sub.L and L are estimated from a down-scaled image, respectively. The capacity signal K.sub.L and the luminance signal L are derived from the obtained color value. Further, the capacity signal, K.sub.L is derived by first applying a suitable operator S to reduce the image from scanner resolution to the watermark resolution and then converting the obtained color values to CMY estimates such that K.sub.L=min(C,M,Y) Alternatively, K-capacity is derived from the amount, K.sub.L, y, comprises first converting the obtained color values to CMY estimates and applying a suitable operator S to reduce the image from scanner resolution to the watermark resolution such that K.sub.L=min(S(C),S(M),S(Y)); wherein L is described by a linear combination of scan signals RGB, such that L=k.sub.1S(R)+k.sub.2S(G)+k.sub.3S(B). The value of K.sub.H is determined by first converting the obtained color values to CMY estimates. The estimates determine K-colorant amount at each pixel such that: K=min(C,M,Y). A suitable operator S is applied to reduce the image from scanner resolution to the watermark resolution.