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BlackInformation Structure

Contains information for device models that have a black color channel.

Syntax

typedef struct _BlackInformation {
  BOOL  bBlackOnly;
  FLOAT blackWeight;
} BlackInformation;

Members

bBlackOnly

An indicator whether the source color contains only black. This value can only be true if both of the following apply:

  • the source device has a black channel
  • the PRESERVEBLACK flag is set to true. This flag is in the dwFlags parameter of a Color Management Module (CMM) transform function.
blackWeight

A value between 0.0 and 1.0 that indicates the relative amount of black to use in the output. A value of 0.0 means that no black is used; a value of 1.0 means that the maximum amount of black is used.

Remarks

If the source device does not support a black channel, then WCS sets bBlackOnly to FALSE.

If bBlackOnly is TRUE, then WCS generates an output device control value where, at most, the black channel will be non-zero. This only happens if the BlackPreservation flag was set in WCS. Note that in such cases, the device model may not be providing the closest colorimetric match to the supplied value.

Black preservation is only performed when both the source and destination devices support a black channel. If black is being preserved with these devices, then for each source device control value, where all channels other than the black channel are zero, the bBlackOnly flag is TRUE. Note that this means that a value where all channels are zero will also set bBlackOnly to TRUE.

blackWeight gives us information about the device control values used in the source device.

  • For source devices with a black channel, blackWeight is set to the black value.
  • For source devices without a black channel, the black weight is computed using a combination of color purity and relative lightness.

    Color purityis defined as (maxColorant - minColorant)/maxColorant

    Relative lightness is defined as (the lightness of the color in appearance space - minimum lightness of destination device) / (maximum lightness of destination device - minimum lightness of destination device)

    For RGB devices, blackWeight = (1 - colorPurity) * (1 - relativeLightness)

    For CMYK devices, blackWeight = colorPurity * (1 - relativeLightness)

    WCS is responsible for initializing the BlackInformation structure.

If bBlackOnly is FALSE, then the baseline device models for devices with a black channel will use the blackWeight to guide the creation of a colorimetrically appropriate output pixel value. For CMYK devices, blackWeight provides WCS's initial estimation of a K value and it searches for C, M, and Y values that will lead to the correct colorimetry. If it does not find a match, it adjusts the K value and searches again.

You can set plug-ins to either support or ignore the BlackInformation.

Requirements

Minimum supported client

Windows Vista

Minimum supported server

Windows Server 2008

Header

WcsPlugIn.h

See Also

Basic Color Management Concepts
Structures

 

 

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Build date: 11/16/2010

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