A stain degree determination apparatus comprising: a feature extracting unit which extracts a plurality of feature information items from an image information containing an inherent variation, a separating unit which separates the plurality of feature information items extracted from the image information by the feature extracting unit into a component of the inherent variation and a residual component other than the above component, and a determining unit which extracts a component of a stain variation indicating a stain degree in the image information from the residual component obtained by the separating unit and determines a stain degree in the image information based on a magnitude of the extracted stain variation component, wherein the image information is image information obtained by reading a printed matter on which a pattern is printed, the inherent variation is a printing variation caused by a variation in printing for the printed matter, and the stain variation is a variation in a stain caused on the printed matter by an external factor, and wherein the separating unit transforms a set of the plurality of feature information items into a first partial vector containing the inherent variation component and a plurality of other residual components, and the determining unit transforms a set of the plurality of residual components into a second partial vector containing a stain variation component and a component other than the preceding component and determines the stain degree in the image information as the magnitude of the stain variation component in the second partial vector, wherein the apparatus further comprises a first learning unit which generates a first transformation matrix to transform a set of the plurality of feature information items in the image information into the inherent variation component and a plurality of other residual components by main component analysis for a set of a plurality of feature information items in an image information containing no stain, wherein the apparatus further comprises a second learning unit which generates a second transformation matrix to transform a residual component obtained by removing the inherent variation component from a set of the plurality of feature information items in an image information containing a stain into a stain variation component and a component other than the preceding component, wherein the plurality of feature information items extracted by the feature extracting unit are color image information. a feature extracting unit which extracts a plurality of feature information items from an image information containing an inherent variation, a separating unit which separates the plurality of feature information items extracted from the image information by the feature extracting unit into a component of the inherent variation and a residual component other than the above component, and a determining unit which extracts a component of a stain variation indicating a stain degree in the image information from the residual component obtained by the separating unit and determines a stain degree in the image information based on a magnitude of the extracted stain variation component, wherein the image information is image information obtained by reading a printed matter on which a pattern is printed, the inherent variation is a printing variation caused by a variation in printing for the printed matter, and the stain variation is a variation in a stain caused on the printed matter by an external factor, and wherein the separating unit transforms a set of the plurality of feature information items into a first partial vector containing the inherent variation component and a plurality of other residual components, and the determining unit transforms a set of the plurality of residual components into a second partial vector containing a stain variation component and a component other than the preceding component and determines the stain degree in the image information as the magnitude of the stain variation component in the second partial vector, wherein the apparatus further comprises a first learning unit which generates a first transformation matrix to transform a set of the plurality of feature information items in the image information into the inherent variation component and a plurality of other residual components by main component analysis for a set of a plurality of feature information items in an image information containing no stain, wherein the apparatus further comprises a second learning unit which generates a second transformation matrix to transform a residual component obtained by removing the inherent variation component from a set of the plurality of feature information items in an image information containing a stain into a stain variation component and a component other than the preceding component, wherein the plurality of feature information items extracted by the feature extracting unit are color image information.