An image object. This will be an /XObject dictionary in the document. This
includes description and data. The diectionary includes:
Type: | (name, Optional) The type of PDF object
that this dictionary describes; if present, must be /XObject for an image
XObject.
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Subtype: | (name, Required) The type of XObject that this dictionary describes; must
be /Image for an image /XObject.
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Width: | (integer, Required) The width of the image, in samples.
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Height: | (integer, Required) The height of the image, in samples.
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ColorSpace: | (name or array, Required for images, except those that use the /JPXDecode
filter; not allowed 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.
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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
components. 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 particular, a
CCITTFaxDecode or JBIG2Decode filter always delivers 1-bit samples, 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 ignored if present. The bit depth is determined
in the process of decoding the JPEG2000 image.
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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 230). Default value: the current rendering intent in the
graphics state.
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ImageMask: | (boolean, Optional) A flag indicating whether the image is to be treated as
an image mask (see Section 4.8.5, “Masked Images”). If this flag is true,
the value of /BitsPerComponent must be 1 and Mask and /ColorSpace should
not be specified; unmasked areas are painted using the current nonstroking
color. Default value: false.
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Mask: | (stream or array, Optional except for image masks; not allowed for image
masks; PDF 1.3) An image XObject defining
an image mask to be applied to this image (see “Explicit Masking” on page
321), or an array specifying a range of colors to be applied to it as a
color key mask (see “Color Key Masking” on page 321). If ImageMask is true,
this entry must not be present. (See implementation note 51 in Appendix H.)
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Decode: | (array, Optional) An array of numbers describing how to map image samples
into the range of values appropriate for the image’s color space (see
“Decode Arrays” on page 314). If ImageMask is true, the array must be
either [0 1] or [1 0]; otherwise, its length must be twice the number of
color components required by ColorSpace. If the image uses the JPXDecode
filter and ImageMask is false, Decode is ignored. Default value: see
“Decode Arrays” on page 314.
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Interpolate: | (boolean, Optional) A flag indicating whether image interpolation is to be
performed (see “Image Interpolation” on page 316).
Default value: false.
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Alternates: | (array, Optional; PDF 1.3) An array of
alternate image dictionaries for this image (see “Alternate Images” on page
317). The order of elements within the array has no significance. This
entry may not be present in an image XObject that is itself an alternate
image.
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SMask: | (stream, Optional; PDF 1.4) A subsidiary
image XObject defining a soft-mask image (see “Soft-Mask Images” on page
522) to be used as a source of mask shape or mask opacity values in the
transparent imaging model. The alpha source parameter in the graphics state
determines whether the mask values are interpreted as shape or opacity. If
present, this entry overrides the current soft mask in the graphics state,
as well as the image’s Mask entry, if any. (However, the other transparency
related graphics state parameters—blend mode and alpha constant—remain in
effect.) If SMask is absent, the image has no associated soft mask
(although the current soft mask in the graphics state may still apply).
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SMaskInData: | (integer, Optional for images that use the JPXDecode filter, meaningless
otherwise; PDF 1.5) A code specifying how
soft-mask information (see “Soft-Mask Images” on page 522) encoded with
image samples should be used: (0) If present, encoded soft-mask image
information should be ignored. (1) The image’s data stream includes encoded
soft-mask values. An application can create a soft-mask image from the
information to be used as a source of mask shape or mask opacity in the
transparency imaging model. (2) The image’s data stream includes color
channels that have been preblended with a background; the image data also
includes an opacity channel. An application can create a soft-mask image
with a Matte entry from the opacity channel information to be used as a
source of mask shape or mask opacity in the transparency model.
- If this entry has a nonzero value, SMask should not
be specified. See also Section 3.3.8, “JPXDecode Filter.” Default value: 0.
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Name: | (name, Required in PDF 1.0; optional
otherwise) The name by which this image XObject is referenced in the
XObject subdictionary of the current resource dictionary (see Section
3.7.2, “Resource Dictionaries”). Note: This entry is obsolescent and its
use is no longer recommended. (See implementation note 52 in Appendix H.)
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StructParent: | (integer, Required if the image is a structural content item; PDF 1.3) The integer key of the image’s entry
in the structural parent tree (see “Finding Structure Elements from Content
Items” on page 797).
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ID: | (string, Optional; PDF 1.3; indirect
reference preferred) The digital identifier of the image’s parent Web
Capture content set (see Section 10.9.5, “Object Attributes Related to Web Capture”).
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OPI: | (dictionary, Optional; PDF 1.2) An OPI
version dictionary for the image (see Section 10.10.6, “Open Prepress
Interface (OPI)”). If ImageMask is true, this entry is ignored.
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Metadata: | (stream, Optional; PDF 1.4) A metadata
stream containing metadata for the image (see Section 10.2.2, “Metadata
Streams”).
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OC: | (dictionary, Optional; PDF 1.5) An optional
content group or optional content membership dictionary (see Section 4.10,
“Optional Content”), specifying the optional content properties for this
image XObject. Before the image is processed, its visibility is determined
based on this entry. If it is determined to be invisible, the entire image
is skipped, as if there were no Do operator to invoke it.
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