Named color database resources

(Required) a procedure to determine if this colorant should be replaced by this resource, and to obtain its solid color equivalent. The procedure is called with the NCD and the name of the colorant in question on the operand stack (as a string or name).

If this colorant is not to be replaced, the procedure should remove both operands and return false:

NCD colorant -> Lookup -> false

If this colorant is to be replaced, two approaches are supported:

Variant 1:

If all colorants to be replaced by this NCD will use the same color space for the replacement, then define the ColorSpace entry in the NCD as described above, and return an array of color values for the solid of the colorant being replaced in that color space and true on the operand stack:

NCD colorant -> Lookup -> [ solid-color-values ] true

The array must include the correct number of color values, in the correct range, for the ColorSpace specified in the NCD. As an example, if ColorSpace is [ /DeviceCMYK] , then the color value array returned for a bright red colorant might be [ 0 1 1 0 ].

This array must be unique to each call to Lookup. The means of obtaining the solid colors is not defined, but some methods are in Named color lookup examples.

If this variant is used, TintTransform must be defined in the NCD; see below.

Variant 2:

Alternatively, the Lookup procedure can dynamically select or construct the color space in which the values are returned and include the color space and tint transform in a dictionary that is returned with true:

NCD colorant -> Lookup -> dict true

The returned dictionary may contain a ColorSpace entry, exactly as described above; if ColorSpace is not defined in the returned dictionary then it must be defined in the NCD itself. TintTransform must be defined in the returned dictionary; any TintTransform defined in the NCD is ignored.

The TintTransform in the returned dictionary must be a complete procedure, exactly as would be used as the fourth element of a color space array. It must accept a single value and return a set of color values suitable for the selected ColorSpace. An example of such a tint transform for a DeviceCMYK ColorSpace:

{
  [ 0.0 0.8 0.8 0.3 ]
  {1 index mul exch } forall pop% the tint
} bind

Procedure, required either in the NCD or in the dictionary returned by Lookup, but note that the values must be structured differently for Variants 1 and 2 above.

Variant 1:

In the case where the Lookup procedure returns an array a color values, a TintTransform procedure must be defined in the NCD. In this case the procedure must consume a color value for the spot being replaced, and the array of color values as returned by Lookup.

tint [solid_1 ... solid_N] -> TintTransform -> tint_1 ... tint_N

An example might be:

/TintTransform {
  {
    1 index mul exch
  } forall pop
} bind

Variant 2:

In the case where the Lookup procedure returns a dictionary in which TintTransform is defined, any TintTransform defined in the NCD is ignored.

(Optional) An integer, name, string, or null.

Default: null.

Subject to the following caveats, after extracting the named color's equivalent value from the resource, the color is passed directly to the /NextDevice transform with the matching ID, see ID in setreproduction. Any transforms before this in the color pipeline are bypassed. In a color configuration with several /NextDevice transforms, this allows resources to have their colors processed by the most appropriate /NextDevice transform. For example, if there are several CMYK /NextDevice transforms in the pipeline each with different printing conditions.

The ID key only has effect if the ColorSpace of the resource is /DeviceCMYK, /DeviceRGB, /DeviceGray, /DeviceN, or /Separation; otherwise, it is ignored.

If an ID key is present and not null, setreproduction must be configured with a /NextDevice dictionary containing a matching ID value; see Illustrations of controlled merging of spots with color pipelines. Otherwise, an error is thrown. The matching /NextDevice may be configured at any position in a color pipeline with many /NextDevice transforms.

All of the colorants present in the ColorSpace entry must be accepted by the matching /NextDevice (that is, the input colorants of the matching /NextDevice must be a non-strict superset of the resource's ColorSpace. An error is thrown if one or more of the colorants of the resource aren't accepted by the /NextDevice.

For the purpose of ID matching, names and strings are considered equivalents.

It is important that a tint of 0 should map to no ink, and that a tint of 1 should map to the solid color. Failure to observe these restrictions may result in artifacts when spots are used in transparency jobs and when OverprintPreview is active.