1. A computerized method for evaluating a patent document, comprising: in a computer having a digital processor configured to perform the following: (a) introducing one or more patent indices, characterizing different aspects of the patent document and contributing to a quality of the patent document, the quality of the patent document being associated with a monetary value of the patent document, each patent index having a single numerical value and being defined on a bounded interval for said each patent index, having respective minimal and maximal values; (b) performing a non-linear transformation of said patent indices into a Patent Quality (PQ) index, which characterizes the quality of the patent document by a single numerical value, said Patent Quality index being defined on a bounded interval for the Patent Quality index having respective PQ min and PQ max values; said transformation: being continuous, monotonous with respect to each said one or more patent indices; being non-linear with respect to at least one of said one or more patent indices; wherein said patent indices and said non-linear transformation are chosen so as to satisfy the following: tending of any one of said patent indices substantially to a respective minimal value, results in said Patent Quality index tending substantially to one of the following, independent of values of other patent indices: the PQ min ; the PQ max ; wherein said non-linear transformation has a parameter of non-linearity expressed as a real number; wherein said non-linear transformation is a single-valued transformation providing a single numerical value for the PQ index for any parameter of non-linearity; and (c) visualizing the quality of the patent document by using a color coding providing a correspondence between the single numerical value of Patent Quality index and a color formed by a mixture of one or more wavelengths of a visible part of light spectrum.