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        SECTION 7.5                                              Specifying Transparency in PDF



        KEY                        RESTRICTION

        Width                      If a Matte entry (see Table 7.12, below) is present, must be the
                                   same as the Width value of the parent image; otherwise inde-
                                   pendent of it. Both images are mapped to the unit square in
                                   user space (as are all images), regardless of whether the sam-
                                   ples coincide individually.

        Height                     Same considerations as for Width.

        ColorSpace                 Required; must be DeviceGray.

        BitsPerComponent           Required.

        Intent                     Ignored.

        ImageMask                  Must be false or absent.

        Mask                       Must be absent.

        SMask                      Must be absent.

        Decode                     Default value: [ 0 1 ].

        Interpolate                Optional.

        Alternates                 Ignored.

        Name                       Ignored.

        StructParent               Ignored.

        ID                         Ignored.

        OPI                        Ignored.


                       TABLE 7.12 Additional entry in a soft-mask image dictionary
KEY     TYPE           VALUE

Matte   array          (Optional; PDF 1.4) An array of component values specifying the matte color with
                       which the image data in the parent image has been preblended. The array consists of n
                       numbers, where n is the number of components in the color space specified by the
                       ColorSpace entry in the parent image’s image dictionary; the numbers must be valid
                       color components in that color space. If this entry is absent, the image data is not
                       preblended.

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