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Black preservation

This page applies to Harlequin v13.1r0 and later; both Harlequin Core and Harlequin MultiRIP.

Color managing black usually results in a non-pure color that could be undesirable for text or linework. Black preservation is used for preserving black channel values across color transforms, both with and without color management. There are two distinct types of black preservation: 100% black and black tint, which applies to all black values. The specific details of each is described in the subsections for each, while features common to both are described in this section. It is possible to have both methods enabled at the same time.

Black preservation only applies to black linework and text objects (that is, it does not apply to images or shadings). More specifically, black preservation does not apply to Picture and Shading objects (see Object types). The definition of a black object is an object painted in one of these allowed color spaces and with restrictions on the allowed color values supplied by the job, before color management:

  • /DeviceCMYK with color values of 0 0 0 k,
  • /DeviceRGB with color values of r g b where r = g = b,
  • /DeviceGray with any color value,
  • /CalRGB with color values of r g b where r = g = b,
  • /CalGray with any color value,
  • /ICCBased when the device space of the ICC profile is one of CMYK, RGB, Gray, with color values the same as for the corresponding device space,
  • /Separation when the colorant name is Black or Gray, not treated as a spot (see below), with any color value,
  • /DeviceN when one of the components is Black or Gray, not treated as a spot (see below), and all other components have a color value = 0,
  • /Indexed, when the base space is one of the above,
  • Uncolored /Pattern, when the underlying space of the uncolored pattern is one of the above,

with the common feature of requiring a device-like color space that represents a pure process black. 100% black preservation has the additional restriction of requiring a solid black.

For /Separation and /DeviceN color spaces, Gray will be treated as a spot if the ProcessColorModel (PCM) is /DeviceCMYK, and both Black and Gray may be a spot if the PCM is /DeviceN. If treated as a spot, black preservation will not be applied. Neither Black nor Gray will be treated as a spot if the PCM is /DeviceRGB or /DeviceGray.

Black preservation is implemented using this method on black objects:

  • The black is removed from the color values.
  • Color convert using the same color transform that would be used without black preservation.
  • The black is merged back into the resulting color.

This method is used because it avoids overprinted black objects knocking out when the color-managed white of the page lays down ink (for example, in an emulation workflow where a proofing device is emulating the color of newsprint).

The color space of the output device must be one of /DeviceCMYK, /DeviceRGB or /DeviceGray, or is a /DeviceN space that has a black colorant (that is, it cannot be a /DeviceN space without a black colorant).

Black preservation can be controlled for specific object types and color models (see Alternate CMMs: CMM custom color spaces). An example of use would be for preserving black for only black text, not linework. A more specific example would be for only RGB black text, with non-RGB text color managed normally.

Black preservation works with OverprintPreview (see PDF/X Color), when black objects overprint other objects. With OverprintPreview, objects are first rendered into the implicit page group, after which the original objects are represented as pixels in the page group’s backdrop. When a black object touches a pixel, black preservation is applied to the color transform of that pixel to the output space with the same method used for objects.

Black preservation is only applied to opaque objects; it is not applied when transparency effects are active. Black preservation is applied to opaque objects within opaque transparency groups.

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