rfc2879.txt

RFC 的详细文档！

   -  ASN.1 identifier associated with this feature tag:

        1.3.6.1.8.1.9

   -  Summary of the media features indicated:

        This feature is used to indicate differential horizontal and
        vertical resolution capability.  In the absence of this
        feature, horizontal and vertical resolutions are presumed to
        be the same.

        When this feature tag is specified, any declared resolution
        (dpi) is presumed to apply to the horizontal axis, and the
        vertical resolution is obtained by dividing that declared
        resolution by the resolution ratio.

        The value of this feature is a pure number, since it
        represents the ratio of two resolution values.

   -  Values appropriate for use with this feature tag:

        Rational (>0)

   -  The feature tag is intended primarily for use in the following
      applications, protocols, services, or negotiation mechanisms:

        Internet fax, and other print or display applications that
        must handle differential horizontal and vertical resolution
        values.

   -  Examples of typical use:

        The following example describes a fax resolution of 204 dpi
        horizontally by 391 dpi vertically:

        (& (dpi=204) (dpi-xyratio=204/391) )





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   -  Related standards or documents:

        The memo "Media Features for Display, Print, and Fax" [3]
        describes a feature (dpi) for measuring document resolution.

   -  Interoperability considerations:

        When interoperating with an application that does not
        recognize the differential resolution feature, resolution
        matching may be performed on the basis of the horizontal
        resolution only, so aspect ratio information may be lost.

   -  Related feature tags:

        dpi                   [3]
        size-x                [this document]
        size-y                [this document]

   -  Intended usage:

        Internet fax

   -  Author/Change controller:

        IETF

A.3 Color levels

   -  Media Feature tag name(s):

        color-levels

   -  ASN.1 identifier associated with this feature tag:

        1.3.6.1.8.1.10

   -  Summary of the media features indicated:

        This feature tag is used to indicate a number of different
        image data pixel color values.

        When mapped (palletized) color is used, this is generally
        different from the number of different colors that can be
        represented through the color mapping function.

        This feature tag is used in conjunction with a 'color' feature
        having a value other than 'Binary'.




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   -  Values appropriate for use with this feature tag:

        Integer  (>=2)

   -  The feature tag is intended primarily for use in the following
      applications, protocols, services, or negotiation mechanisms:

        Color image printing or display applications where the data
        resource used may depend upon color handling capabilities of
        the recipient.

   -  Examples of typical use:

        To describe recipient capabilities:
        (& (color=limited) (color-levels<=6) )
        (& (color=grey)    (color-levels<=64) )
        (& (color=mapped)  (color-levels<=240) )
        (& (color=full)    (color-levels<=16777216) )

        To describe capabilities used by a document:
        (& (color=limited) (color-levels=4) )
        (& (color=grey)    (color-levels=48) )
        (& (color=mapped)  (color-levels=100) )
        (& (color=full)    (color-levels=32768) )

   -  Related standards or documents:

        The memo "Media Features for Display, Print, and Fax" [3]
        describes a feature (color) for indicating basic color
        capabilities.

   -  Interoperability considerations:

        The actual number of color values used by a document does not,
        in general, exactly match the number that can be handled by a
        recipient.  To achieve a feature match, at least one must be
        declared as an inequality (i.e. not both as equalities).

        It is recommended that a recipient declares the number of
        color values that it can handle as an inequality (<=), and a
        data resource declares the number of colors that it uses with
        an equality, as shown in the examples above.









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   -  Security considerations:

      - Privacy concerns, related to exposure of personal information:
           Where feature matching is used to select content applicable
           to the physical abilities of a user, unusual values for this
           feature tag might give an indication of a user's restricted
           abilities.

   -  Related feature tags:

        color                 [3]
        color-space           [this document]

   -  Intended usage:

        Internet fax
        Color image scanning/rendering applications

   -  Author/Change controller:

        IETF

A.4 Color space

   -  Media Feature tag name(s):

        color-space

   -  ASN.1 identifier associated with this feature tag:

        1.3.6.1.8.1.11

   -  Summary of the media features indicated:

        This feature indicates a color space.

        A color space value provides two types of information:
        o  the color model used to represent a color value, including
           the number of color components
        o  a mapping between color values and their physical
           realizations

        Device color space values are defined for applications where
        the general color representation used is significant, but
        exact color rendering is left to the device used.  Device
        color spaces defined here have values of the form 'Device-
        xxx'.




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        Calibrated color space values are provided for use with a
        rendering system that is calibrated with respect to some
        indicated definition, and capable of processing device-
        independent color information accordingly.

   -  Values appropriate for use with this feature tag:

        Token

        Device color      Device-RGB   (device dependent RGB)
        spaces:           Device-CMY   (device dependent CMY)
                          Device-CMYK  (device dependent CMYK)

        Calibrated color  CIELAB       (per T.42 [9])
        space:

                          (may be extended by further registrations)

        'Color-space=CIELAB' indicates the CIE L*a*b* colour space,
        using CIED50 illuminant and its perfectly diffuse reflecting
        white point (per T.42 [9]).

   -  The feature tag is intended primarily for use in the following
      applications, protocols, services, or negotiation mechanisms:

        Color image printing and display applications where the data
        resource used may depend upon color handling capabilities of
        the recipient.

        Scanning applications where the data transferred may depend
        upon the image generation capabilities of the originator.

   -  Examples of typical use:

        To describe rendering or scanning capabilities:

        (color-space=[Device-RGB,CIELAB])

        To describe capabilities assumed by a document for which
        approximate color reproduction is required:

        (color-space=Device-RGB)

        To describe capabilities assumed by a document for which exact
        color reproduction is required:

        (color-space=CIELAB)




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   -  Related standards or documents:

        CIELAB color space is defined in [19]

        CIELAB use for fax is described in ITU T.42 [9]

   -  Interoperability considerations:

        A color-handling receiver should indicate any appropriate
        device color space capability, in addition to any calibrated
        color spaces that it may support.

        Calibrated color spaces are intended to be used when precise
        color matching is required;  otherwise, if applicable, a
        device color space (color-space=Device-xxx) should be
        indicated.

        Documents for which exact color matching is not important
        should indicate a device color space capability, if
        applicable.

        These principles allow sender/receiver feature matching to be
        achieved when exact color matching is not required.

   -  Security considerations:

      - Privacy concerns, related to exposure of personal information:
           Where feature matching is used to select content applicable
           to the physical abilities of a user, unusual values for this
           feature tag might give an indication of a user's restricted
           abilities.

      - Denial of service concerns related to consequences of
        specifying incorrect values:
           Failure to indicate a generic color space capability for a
           device may lead to failure to match color space for an
           application or document that does not require an exact color
           match.

   -  Related feature tags:

        color                 [3]

   -  Related media types or data formats:

        TIFF-FX               [7]





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   -  Intended usage:

        Internet fax
        Color image scanning/rendering applications

   -  Author/Change controller:

        IETF

A.5 CIELAB color illuminant

   -  Media Feature tag name(s):

        color-illuminant

   -  ASN.1 identifier associated with this feature tag:

        1.3.6.1.8.1.29

   -  Summary of the media features indicated:

        This feature indicates a color illuminant.  This has the
        effect of modifying the color space calibration to reflect the
        use of different sources of illumination.

        A color-illuminant value would normally be used only with a
        calibrated color space.

   -  Values appropriate for use with this feature tag:

        Token

        CIELAB illuminant D50
        values:           D65
                          D75
                          SA
                          SC
                          F2
                          F7
                          F11

        Defined by color  CTnnnn wh