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SECTION 4.6                                                                  Patterns



difference arises because the two color spaces are not linear relative to each other.
Shadings are rendered according to the following rules:

• If ColorSpace is a device color space different from the native color space of the
  output device, color values in the shading are converted to the native color
  space using the standard conversion formulas described in Section 6.2, “Con-
  versions among Device Color Spaces.” To optimize performance, these conver-
  sions may take place at any time (before or after any interpolation on the color
  values in the shading). Thus, shadings defined with device color spaces may
  have color gradient fills that are less accurate and somewhat device-dependent.
  (This does not apply to axial and radial shadings—shading types 2 and 3—be-
  cause those shading types perform gradient fill calculations on a single variable
  and then convert to parametric colors.)
• If ColorSpace is a CIE-based color space, all gradient fill calculations are per-
  formed in that space. Conversion to device colors occurs only after all interpo-
  lation calculations have been performed. Thus, the color gradients are device-
  independent for the colors generated at each point.
• If ColorSpace is a Separation or DeviceN color space and the specified colo-
  rants are supported, no color conversion calculations are needed. If the speci-
  fied colorants are not supported (so that the space’s alternate color space must
  be used), gradient fill calculations are performed in the designated Separation
  or DeviceN color space before conversion to the alternate space. Thus, non-
  linear tint transformation functions are accommodated for the best possible
  representation of the shading.
• If ColorSpace is an Indexed color space, all color values specified in the shading
  are immediately converted to the base color space. Depending on whether the
  base color space is a device or CIE-based space, gradient fill calculations are
  performed as stated above. Interpolation never occurs in an Indexed color
  space, which is quantized and therefore inappropriate for calculations that as-
  sume a continuous range of colors. For similar reasons, an Indexed color space
  is not allowed in any shading whose color values are generated by a function;
  this rule applies to any shading dictionary that contains a Function entry.

Shading Types

In addition to the entries listed in Table 4.28, all shading dictionaries have entries
specific to the type of shading they represent, as indicated by the value of their

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