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                                                   340
          CHAPTER 4                                                                       Graphics




                     TABLE 4.39 Additional entries specific to an image dictionary
KEY                TYPE           VALUE

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

Subtype            name           (Required) The type of XObject that this dictionary describes; must be
                                  Image for an image XObject.

Width              integer        (Required) The width of the image, in samples.

Height             integer        (Required) The height of the image, in samples.

ColorSpace         name or        (Required for images, except those that use the JPXDecode filter; not allowed
                   array          for image masks) The color space in which image samples are specified; it
                                  can be any type of color space except Pattern.
                                  If the image uses the JPXDecode filter, this entry is optional:
                                  • If ColorSpace is present, any color space specifications in the JPEG2000
                                    data are ignored.
                                  • If ColorSpace is absent, the color space specifications in the JPEG2000
                                    data are used. The Decode array is also ignored unless ImageMask is
                                    true.

BitsPerComponent   integer        (Required except for image masks and images that use the JPXDecode filter)
                                  The number of bits used to represent each color component. Only a single
                                  value may be specified; the number of bits is the same for all color compo-
                                  nents. Valid values are 1, 2, 4, 8, and (in PDF 1.5) 16. If ImageMask is true,
                                  this entry is optional, and if specified, its value must be 1.
                                  If the image stream uses a filter, the value of BitsPerComponent must be
                                  consistent with the size of the data samples that the filter delivers. In par-
                                  ticular, a CCITTFaxDecode or JBIG2Decode filter always delivers 1-bit sam-
                                  ples, a RunLengthDecode or DCTDecode filter delivers 8-bit samples, and
                                  an LZWDecode or FlateDecode filter delivers samples of a specified size if
                                  a predictor function is used.
                                  If the image stream uses the JPXDecode filter, this entry is optional and ig-
                                  nored if present. The bit depth is determined in the process of decoding
                                  the JPEG2000 image.

Intent             name           (Optional; PDF 1.1) The name of a color rendering intent to be used in
                                  rendering the image (see “Rendering Intents” on page 260). Default value:
                                  the current rendering intent in the graphics state.

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