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                                            289
    SECTION 4.6                                                                Patterns



    defining graphical figures whose colors are to be specified separately each time
    they are used. Specifically, the restriction applies in these circumstances:

    • In any glyph description that uses the d1 operator (see Section 5.5.4, “Type 3
      Fonts”)
    • In the content stream of an uncolored tiling pattern (see “Uncolored Tiling Pat-
      terns” on page 298)

    In these circumstances, the following actions cause an error:

    • Invoking any of the following operators:
        CS                        scn                      K
        cs                        G                        k
        SC                        g                        ri
        SCN                       RG                       sh
        sc                        rg


    • Invoking the gs operator with any of the following entries in the graphics state
      parameter dictionary:

        TR                        BG                       UCR
        TR2                       BG2                      UCR2
        HT


    • Painting an image. However, painting an image mask (see “Stencil Masking” on
      page 350) is permitted because it does not specify colors; instead, it designates
      places where the current color is to be painted.


4.6 Patterns

    When operators such as S (stroke), f (fill), and Tj (show text) paint an area of the
    page with the current color, they ordinarily apply a single color that covers the
    area uniformly. However, it is also possible to apply “paint” that consists of a re-
    peating graphical figure or a smoothly varying color gradient instead of a simple
    color. Such a repeating figure or smooth gradient is called a pattern. Patterns are
    quite general, and have many uses; for example, they can be used to create various
    graphical textures, such as weaves, brick walls, sunbursts, and similar geometrical
    and chromatic effects. (See implementation note 50 in Appendix H.)

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