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SECTION 4.3 Graphics State
KEY TYPE DESCRIPTION
AIS boolean (Optional; PDF 1.4) The alpha source flag (“alpha is shape”), specifying
whether the current soft mask and alpha constant are to be interpreted as
shape values (true) or opacity values (false).
TK boolean (Optional; PDF 1.4) The text knockout flag, which determines the behavior of
overlapping glyphs within a text object in the transparent imaging model (see
Section 5.2.7, “Text Knockout”).
Example 4.1 shows two graphics state parameter dictionaries. In the first, auto-
matic stroke adjustment is turned on, and the dictionary includes a transfer func-
tion that inverts its value, f (x) = 1 − x. In the second, overprint is turned off, and
the dictionary includes a parabolic transfer function, f (x) = (2x − 1) 2, with a sam-
ple of 21 values. The domain of the transfer function, [ 0.0 1.0 ], is mapped to
[ 0 20 ], and the range of the sample values, [ 0 255 ], is mapped to the range of
the transfer function, [ 0.0 1.0 ].
Example 4.1
10 0 obj % Page object
<< /Type /Page
/Parent 5 0 R
/Resources 20 0 R
/Contents 40 0 R
>>
endobj
20 0 obj % Resource dictionary for page
<< /ProcSet [ /PDF /Text ]
/Font << /F1 25 0 R >>
/ExtGState << /GS1 30 0 R
/GS2 35 0 R
>>
>>
endobj
30 0 obj % First graphics state parameter dictionary
<< /Type /ExtGState
/SA true
/TR 31 0 R
>>
endobj
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