Fast and accurate color measurement devices would have benefitted printing in general and specifically commercial and industrial printing presses, however, such devices are expensive and are therefore not always available. On the other hand, a scanner is cheap and available in most print services providers, and is sometimes even integrated in the output paper path of commercial presses, e.g. the HP7500 press. It is commonly agreed that scanners are not color measurement devices - certainly not accurate ones. This paper shows feasibility of providing printer output spectrum estimation using a scanner as the measuring device. Such a method could further be used for colorimetry and color characterization. To do that we need to estimate the color specification of a scanner - or - the mapping function from the spectrum to the scanner measurements, which we will consequently invert. Unlike traditional methods that ignore the printing process, we propose to use the printer color model as a prior knowledge to perform accurate spectrum estimation. The applicability generality and high quality of the proposed method are demonstrated on two different printing processes: a Thermal Inkjet printer and an LEP (HP Indigo) press.