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                                                    358
            CHAPTER 4                                                                      Graphics




                    TABLE 4.45 Additional entries specific to a type 1 form dictionary
KEY              TYPE           VALUE

Type             name           (Optional) The type of PDF object that this dictionary describes; if present,
                                must be XObject for a form XObject.

Subtype          name           (Required) The type of XObject that this dictionary describes; must be Form
                                for a form XObject.

FormType         integer        (Optional) A code identifying the type of form XObject that this dictionary
                                describes. The only valid value defined at the time of publication is 1. Default
                                value: 1.

BBox             rectangle      (Required) An array of four numbers in the form coordinate system (see
                                above), giving the coordinates of the left, bottom, right, and top edges,
                                respectively, of the form XObject’s bounding box. These boundaries are used
                                to clip the form XObject and to determine its size for caching.

Matrix           array          (Optional) An array of six numbers specifying the form matrix, which maps
                                form space into user space (see Section 4.2.3, “Transformation Matrices”).
                                Default value: the identity matrix [ 1 0 0 1 0 0 ].

Resources        dictionary     (Optional but strongly recommended; PDF 1.2) A dictionary specifying any
                                resources (such as fonts and images) required by the form XObject (see Sec-
                                tion 3.7, “Content Streams and Resources”).
                                In PDF 1.1 and earlier, all named resources used in the form XObject must be
                                included in the resource dictionary of each page object on which the form
                                XObject appears, regardless of whether they also appear in the resource dic-
                                tionary of the form XObject. It can be useful to specify these resources in the
                                form XObject’s resource dictionary as well, to determine which resources are
                                used inside the form XObject. If a resource is included in both dictionaries, it
                                should have the same name in both locations.
                                In PDF 1.2 and later versions, form XObjects can be independent of the
                                content streams in which they appear, and this is strongly recommended
                                although not required. In an independent form XObject, the resource dictio-
                                nary of the form XObject is required and contains all named resources used
                                by the form XObject. These resources are not promoted to the outer content
                                stream’s resource dictionary, although that stream’s resource dictionary refers
                                to the form XObject.

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