Abstract: Methods and apparatus, including computer program products, implementing and using techniques for digital rights management. In one aspect, a method is provided. The method includes receiving an electronic document, where the electronic document includes one or more content items, a set of usage rights defining one or more features to be enabled when the document is read by an electronic document reader, and a stored representation. The method further includes generating a representation of invariant content items of the electronic document, comparing the generated representation with the stored representation, and enabling features corresponding to the set of usage rights in the electronic document only if the generated representation and the stored representation are identical, where the features are features performed by the electronic document reader on the electronic document.

Abstract: Methods, systems, and apparatus, including computer program products, for determining a complexity value for a subregion of an electronic document page that includes one or more objects. In one aspect, a method includes dividing a subregion of an electronic document page into a plurality of cells, where the electronic document page includes one or more objects, the objects include one or more transparent objects, the subregion includes at least part of a transparent object, and each cell has an associated cell counter. The method includes, for each object partly or completely located in the subregion, identifying cells that are overlapped by the object, and increasing the associated cell counter for each of the identified cells. The method includes summing all cell counters associated with all cells in the subregion to determine a complexity value for the subregion.

Abstract: Methods and apparatus, including computer program products, implementing and using techniques for establishing trust in an electronic document. An electronic document is received. State dependent content in the electronic document is identified. The state dependent content is content that is renderable to have a several appearances. The electronic document is presented to a user, which includes disclosing the presence of any identified state dependent content in the electronic document.

Abstract: Methods and apparatus, including computer program products, implementing and using techniques for establishing trust in an electronic document. An electronic document is received. State dependent content in the electronic document is identified. The state dependent content is content that is renderable to have a several appearances. The electronic document is presented to a user, which includes disclosing the presence of any identified state dependent content in the electronic document.

Abstract: Methods and apparatus, including computer program products, implementing and using techniques for digital rights management. An electronic document containing one or more content items is provided along with a set of usage rights. The set of usage rights defines one or more features to be enabled when the electronic document is processed in an electronic document reader. A representation of a set of content items of the electronic document that are invariant to operations of the features in the set of usage rights is generated, and a digital signature authorizing the set of usage rights is provided. An electronic document and an electronic document reader are also described.

Abstract: Methods and apparatus, including computer program products, implementing and using techniques for rendering an electronic document page that includes one or more objects. It is determined whether any object of the one or more objects on the document page is a transparent object. If a transparent object is found, the document page is divided into a plurality of subregions. For each subregion, a set of one or more opaque object components is generated for any object having a location in the subregion. The document page is rendered, including separately rendering each of the plurality of subregions.

Abstract: The invention features a method, system, and computer program product. A source bitmap image, a destination bitmap image, a source image feature outline surrounding a source region of the source bitmap image, and a destination image feature outline surrounding a destination region of the destination bitmap image are received. A point-to-point correspondence between the source image feature outline and the destination image feature outline is generated, such that the point-to-point correspondence defines a reshaping of the source image feature outline. An interpolation surface is calculated interpolating an area of the source bitmap image that includes the source region. The interpolation surface is reshaped using the point-to-point correspondence.

Abstract: Edges are detected in a raster image and generate parametric curves from the detected edges. The parametric curves are used to render a scaled version of the raster image. Some embodiments may allow edge locations within a raster image to retain a satisfactory level of sharpness when the raster image is scaled to a larger size.

Abstract: Methods and apparatus, including computer program products, implementing and using techniques for establishing trust in an electronic document. An electronic document is received. State dependent content in the electronic document is identified. The state dependent content is content that is renderable to have a several appearances. The electronic document is presented to a user, which includes disclosing the presence of any identified state dependent content in the electronic document.

Abstract: Methods and apparatus, including computer program products, implementing and using techniques for document authentication. An electronic document is presented to a user. The electronic document has data representing a signed state and a current state. A disallowed difference between the signed state and the current state is detected, based on one or more rules that are associated with the electronic document. A digital signature associated with the electronic document is invalidated in response to the detecting.