Content      ..     3      4      5      6     ..

ISO 32000-1 Document management — Portable document format — Part 1: PDF 1.7 - page 5

Table 70 - Rendering Intents

Name

Description

AbsoluteColorimetric

Colours shall be represented solely with respect to the

light source; no correction shall be made for the output

medium’s white point (such as the colour of unprinted

paper). Thus, for example, a monitor’s white point, which

is bluish compared to that of a printer’s paper, would be

reproduced with a blue cast. In-gamut colours shall be

reproduced exactly; out-of-gamut colours shall be mapped

to the nearest value within the reproducible gamut.

NOTE 1

This style of reproduction has the advantage

of providing exact colour matches from one

output medium to another. It has the

disadvantage of causing colours with Y

values between the medium’s white point and

1.0 to be out of gamut. A typical use might be

for logos and solid colours that require exact

reproduction across different media.

RelativeColorimetric

Colours shall be represented with respect to the

combination of the light source and the output medium’s

white point (such as the colour of unprinted paper). Thus,

a monitor’s white point can be reproduced on a printer by

simply leaving the paper unmarked, ignoring colour

differences between the two media. In-gamut colours shall

be reproduced exactly; out-of-gamut colours shall be

mapped to the nearest value within the reproducible

gamut.

NOTE 2

This style of reproduction has the advantage

of adapting for the varying white points of

different

output media. It has the

disadvantage of not providing exact colour

matches from one medium to another. A

typical use might be for vector graphics.

Saturation

Colours shall be represented in a manner that preserves

or emphasizes saturation. Reproduction of in-gamut

colours may or may not be colourimetrically accurate.

NOTE 3

A typical use might be for business graphics,

where saturation is the most important

attribute of the colour.

Perceptual

Colours shall be represented in a manner that provides a

pleasing perceptual appearance. To preserve colour

relationships, both in-gamut and out-of-gamut colours

shall be generally modified from their precise colourimetric

values.

NOTE 4

A typical use might be for scanned images.

8.6.6

Special Colour Spaces

8.6.6.1

General

Special colour spaces add features or properties to an underlying colour space. There are four special colour

space families: Pattern, Indexed, Separation, and DeviceN.

155

The alternateSpace parameter shall be an array or name object that can be any device or CIE-based colour

space but shall not be another special colour space (Pattern, Indexed, Separation, or DeviceN). When the

colour space is set to a DeviceN space, if any of the component names in the colour space do not correspond

to a colorant available on the device, the conforming reader shall perform subsequent painting operations in

the alternate colour space specified by this parameter.

For NChannel colour spaces, the components shall be evaluated individually; that is, only the ones not present

on the output device shall use the alternate colour space.

The tintTransform parameter shall specify a function (see 7.10, "Functions") that is used to transform the tint

values into the alternate colour space. It shall be called with n tint values and returns m colour component

values, where n is the number of components needed to specify a colour in the DeviceN colour space and m is

the number required by the alternate colour space.

NOTE 4

Painting in the alternate colour space may produce a good approximation of the intended colour when only

opaque objects are painted. However, it does not correctly represent the interactions between an object and its

backdrop when the object is painted with transparency or when overprinting (see 8.6.7, "Overprint Control") is

enabled.

The colour component name None, which may be present only for DeviceN colour spaces that do not have the

NChannel subtype, indicates that the corresponding colour component shall never be painted on the page, as

in a Separation colour space for the None colorant. When a DeviceN colour space is painting the named

device colorants directly, colour components corresponding to None colorants shall be discarded. However,

when the DeviceN colour space reverts to its alternate colour space, those components shall be passed to the

tint transformation function, which may use them as desired.

A DeviceN colour space whose component colorant names are all None shall always discard its output, just

the same as a Separation colour space for None; it shall never revert to the alternate colour space. Reversion

shall occur only if at least one colour component (other than None) is specified and is not available on the

device.

The optional attributes parameter shall be a dictionary (see Table 71) containing additional information about

the components of colour space that conforming readers may use. Conforming readers need not use the

alternateSpace and tintTransform parameters, and may instead use custom blending algorithms, along with

other information provided in the attributes dictionary if present. (If the value of the Subtype entry in the

attributes dictionary is NChannel, such information shall be present.) However, alternateSpace and

tintTransform shall always be provided for conforming readers that want to use them or do not support PDF 1.6.

Table 71 - Entries in a DeviceN Colour Space Attributes Dictionary

Key

Type

Value

Subtype

name

(Optional; PDF 1.6) A name specifying the preferred treatment for the

colour space. Values shall be DeviceN or NChannel. Default value:

DeviceN.

161

Table 71 - Entries in a DeviceN Colour Space Attributes Dictionary (continued)

Key

Type

Value

Colorants

dictionary

(Required if Subtype is NChannel and the colour space includes spot

colorants; otherwise optional) A dictionary describing the individual

colorants that shall be used in the DeviceN colour space. For each entry in

this dictionary, the key shall be a colorant name and the value shall be an

array defining a Separation colour space for that colorant (see 8.6.6.4,

"Separation Colour Spaces"). The key shall match the colorant name

given in that colour space.

This dictionary provides information about the individual colorants that

may be useful to some conforming readers. In particular, the alternate

colour space and tint transformation function of a Separation colour space

describe the appearance of that colorant alone, whereas those of a

DeviceN colour space describe only the appearance of its colorants in

combination.

If Subtype is NChannel, this dictionary shall have entries for all spot

colorants in this colour space. This dictionary may also include additional

colorants not used by this colour space.

Process

dictionary

(Required if Subtype is NChannel and the colour space includes

components of a process colour space, otherwise optional; PDF 1.6) A

dictionary (see Table 72) that describes the process colour space whose

components are included in this colour space.

MixingHints

dictionary

(Optional; PDF 1.6) A dictionary (see Table 73) that specifies optional

attributes of the inks that shall be used in blending calculations when used

as an alternative to the tint transformation function.

A value of NChannel for the Subtype entry indicates that some of the other entries in this dictionary are

required rather than optional. The Colorants entry specifies a colorants dictionary that contains entries for all

the spot colorants in the colour space; they shall be defined using individual Separation colour spaces. The

Process entry specifies a process dictionary (see Table 72) that identifies the process colour space that is

used by this colour space and the names of its components. It shall be present if Subtype is NChannel and the

colour space has process colour components. An NChannel colour space shall contain components from at

most one process colour space.

For colour spaces that have a value of NChannel for the Subtype entry in the attributes dictionary (see

Table 71), the following restrictions apply to process colours:

•

There may be colour components from at most one process colour space, which may be any device or

CIE-based colour space.

•

For a non-CMYK colour space, the names of the process components shall appear sequentially in the

names array, in the normal colour space order (for example, Red, Green, and Blue). However, the names

in the names array need not match the actual colour space names (for example, a Red component need

not be named Red).The mapping of names is specified in the process dictionary (see Table 72 and

discussion below), which shall be present.

•

Definitions for process colorants should not appear in the colorants dictionary. Any such definition shall be

ignored if the colorant is also present in the process dictionary. Any component not specified in the process

dictionary shall be considered to be a spot colorant.

•

For a CMYK colour space, a subset of the components may be present, and they may appear in any order

in the names array. The reserved names Cyan, Magenta, Yellow, and Black shall always be considered

to be process colours, which do not necessarily correspond to the colorants of a specific device; they need

not have entries in the process dictionary.

•

The values associated with the process components shall be stored in their natural form (that is,

subtractive colour values for CMYK and additive colour values for RGB), since they shall be interpreted

162

directly as process values by consumers making use of the process dictionary. (For additive colour spaces,

this is the reverse of how colour values are specified for DeviceN, as described above in the discussion of

the names parameter.)

The MixingHints entry in the attributes dictionary specifies a mixing hints dictionary (see Table 73) that

provides information about the characteristics of colorants that may be used in blending calculations when the

actual colorants are not available on the target device. Conforming readers need not use this information.

Table 72 - Entries in a DeviceN Process Dictionary

KEY

TYPE

VALUE

ColorSpace

name or

(Required) A name or array identifying the process colour space, which

array

may be any device or CIE-based colour space. If an ICCBased colour

space is specified, it shall provide calibration information appropriate for

the process colour components specified in the names array of the

DeviceN colour space.

Components

array

(Required) An array of component names that correspond, in order, to the

components of the process colour space specified in ColorSpace. For

example, an RGB colour space shall have three names corresponding to

red, green, and blue. The names may be arbitrary (that is, not the same as

the standard names for the colour space components) and shall match

those specified in the names array of the DeviceN colour space, even if all

components are not present in the names array.

Table 73 - Entries in a DeviceN Mixing Hints Dictionary

Key

Type

Value

Solidities

dictionary

(Optional) A dictionary specifying the solidity of inks that shall be used in

blending calculations when used as an alternative to the tint

transformation function. For each entry, the key shall be a colorant

name, and the value shall be a number between 0.0 and 1.0. This

dictionary need not contain entries for all colorants used in this colour

space; it may also include additional colorants not used by this colour

space.

A value of 1.0 simulates an ink that completely covers the inks beneath;

a value of 0.0 simulates a transparent ink that completely reveals the

inks beneath. An entry with a key of Default specifies a value that shall

be used by all components in the associated DeviceN colour space for

which a solidity value is not explicitly provided. If Default is not present,

the default value for unspecified colorants shall be 0.0; conforming

readers may choose to use other values.

If this entry is present, PrintingOrder shall also be present.

PrintingOrd

array

(Required if Solidities is present) An array of colorant names,

er

specifying the order in which inks shall be laid down. Each component in

the names array of the DeviceN colour space shall appear in this array

(although the order is unrelated to the order specified in the names

array). This entry may also list colorants unused by this specific

DeviceN instance.

163

Table 73 - Entries in a DeviceN Mixing Hints Dictionary (continued)

Key

Type

Value

DotGain

dictionary

(Optional) A dictionary specifying the dot gain of inks that shall be used

in blending calculations when used as an alternative to the tint

transformation function. Dot gain (or loss) represents the amount by

which a printer’s halftone dots change as the ink spreads and is

absorbed by paper.

For each entry, the key shall be a colorant name, and the value shall be

a function that maps values in the range 0 to 1 to values in the range 0

to 1. The dictionary may list colorants unused by this specific DeviceN

instance and need not list all colorants. An entry with a key of Default

shall specify a function to be used by all colorants for which a dot gain

function is not explicitly specified.

Conforming readers may ignore values in this dictionary when other

sources of dot gain information are available, such as ICC profiles

associated with the process colour space or tint transformation functions

associated with individual colorants.

Each entry in the mixing hints dictionary refers to colorant names, which include spot colorants referenced by

the Colorants dictionary. Under some circumstances, they may also refer to one or more individual process

components called Cyan, Magenta, Yellow, or Black when DeviceCMYK is specified as the process colour

space in the process dictionary. However, applications shall ignore these process component entries if they can

obtain the information from an ICC profile.

NOTE 5

The mixing hints subdictionaries (as well as the colorants dictionary) may specify colorants that are not used in

any given instance of a DeviceN colour space. This allows them to be referenced from multiple DeviceN

colour spaces, which can produce smaller file sizes as well as consistent colour definitions across instances.

For consistency of colour, conforming readers should follow these guidelines:

•

The conforming reader shall apply either the specified tint transformation function or invoke the same

alternative blending algorithm for all DeviceN instances in the document.

NOTE 6

When the tint transformation function is used, the burden is on the conforming writer to guarantee that the

individual function definitions chosen for all DeviceN instances produce similar colour appearances throughout

the document.

•

Blending algorithms should produce a similar appearance for colours when they are used as separation

colours or as a component of a DeviceN colour space.

EXAMPLE 3

This example shows a DeviceN colour space consisting of three colour components named Orange,

Green, and None. In this example, the DeviceN colour space, object 30, has an attributes dictionary

whose Colorants entry is an indirect reference to object 45 (which might also be referenced by attributes

dictionaries of other DeviceN colour spaces). tintTransform1, whose definition is not shown, maps three

colour components (tints of the colorants Orange, Green, and None) to four colour components in the

alternate colour space, DeviceCMYK. tintTransform2 maps a single colour component (an orange tint) to

four components in DeviceCMYK. Likewise, tintTransform3 maps a green tint to DeviceCMYK, and

tintTransform4 maps a tint of PANTONE 131 to DeviceCMYK.

30 0 obj

% Colour space

[

/DeviceN

[ /Orange /Green /None ]

/DeviceCMYK

tintTransform1

<< /Colorants 45 0 R >>

]

endobj

164

/Length 13

>>

stream

{ 0 exch }

endstream

endobj

Nonzero overprint mode shall apply only to painting operations that use the current colour in the graphics state

when the current colour space is DeviceCMYK (or is implicitly converted to DeviceCMYK; see 8.6.5.7, "Implicit

Conversion of CIE-Based Colour Spaces"). It shall not apply to the painting of images or to any colours that are

the result of a computation, such as those in a shading pattern or conversions from some other colour space. It

also shall not apply if the device’s native colour space is not DeviceCMYK; in that case, source colours shall be

converted to the device’s native colour space, and all components participate in the conversion, whatever their

values.

NOTE 2

This is shown explicitly in the alternate colour space and tint transformation function of the DeviceN colour

space (see EXAMPLE 3 in 8.6.6, "Special Colour Spaces").

See 11.7.4, "Overprinting and Transparency", for further discussion of the role of overprinting in the transparent

imaging model.

8.6.8

Colour Operators

Table 74 lists the PDF operators that control colour spaces and colour values. Also colour-related is the

graphics state operator ri, listed in Table 57 and discussed under 8.6.5.8, "Rendering Intents". Colour operators

may appear at the page description level or inside text objects (see Figure 9 in Annex L).

Table 74 - Colour Operators

Operands

Operator

Description

name

CS

(PDF 1.1) Set the current colour space to use for stroking operations. The

operand name shall be a name object. If the colour space is one that can

be specified by a name and no additional parameters (DeviceGray,

DeviceRGB, DeviceCMYK, and certain cases of Pattern), the name may

be specified directly. Otherwise, it shall be a name defined in the

ColorSpace subdictionary of the current resource dictionary (see 7.8.3,

"Resource Dictionaries"); the associated value shall be an array

describing the colour space (see 8.6.3, "Colour Space Families").

The names DeviceGray, DeviceRGB, DeviceCMYK, and Pattern

always identify the corresponding colour spaces directly; they never refer

to resources in the ColorSpace subdictionary.

The CS operator shall also set the current stroking colour to its initial

value, which depends on the colour space:

In a DeviceGray, DeviceRGB, CalGray, or CalRGB colour space, the

initial colour shall have all components equal to 0.0.

In a DeviceCMYK colour space, the initial colour shall be

[0.0

0.0 0.0 1.0 ].

In a Lab or ICCBased colour space, the initial colour shall have all

components equal to 0.0 unless that falls outside the intervals specified

by the space’s Range entry, in which case the nearest valid value shall be

substituted.

In an Indexed colour space, the initial colour value shall be 0.

In a Separation or DeviceN colour space, the initial tint value shall be 1.0

for all colorants.

In a Pattern colour space, the initial colour shall be a pattern object that

causes nothing to be painted.

name

cs

(PDF 1.1) Same as CS but used for nonstroking operations.

171

Table 74 - Colour Operators (continued)

Operands

Operator

Description

c

SC

(PDF 1.1) Set the colour to use for stroking operations in a device, CIE-

1… cn

based (other than ICCBased), or Indexed colour space. The number of

operands required and their interpretation depends on the current

stroking colour space:

For DeviceGray, CalGray, and Indexed colour spaces, one operand

shall be required (n = 1).

For DeviceRGB, CalRGB, and Lab colour spaces, three operands shall

be required (n = 3).

For DeviceCMYK, four operands shall be required (n = 4).

c

SCN

(PDF 1.2) Same as SC but also supports Pattern, Separation, DeviceN

1… cn

c

name

SCN

and ICCBased colour spaces.

1… cn

If the current stroking colour space is a Separation, DeviceN, or

ICCBased colour space, the operands c₁… c_n shall be numbers. The

number of operands and their interpretation depends on the colour space.

If the current stroking colour space is a Pattern colour space, name shall

be the name of an entry in the Pattern subdictionary of the current

resource dictionary

(see

7.8.3, "Resource Dictionaries"). For an

uncoloured tiling pattern (PatternType = 1 and PaintType = 2), c₁… c_n

shall be component values specifying a colour in the pattern’s underlying

colour space. For other types of patterns, these operands shall not be

specified.

c

sc

(PDF 1.1) Same as SC but used for nonstroking operations.

1… cn

c

scn

(PDF 1.2) Same as SCN but used for nonstroking operations.

1… cn

c

name

scn

1… cn

gray

G

Set the stroking colour space to DeviceGray (or the DefaultGray colour

space; see 8.6.5.6, "Default Colour Spaces") and set the gray level to use

for stroking operations. gray shall be a number between 0.0 (black) and

1.0 (white).

gray

g

Same as G but used for nonstroking operations.

r g b

RG

Set the stroking colour space to DeviceRGB (or the DefaultRGB colour

space; see 8.6.5.6, "Default Colour Spaces") and set the colour to use for

stroking operations. Each operand shall be a number between

0.0

(minimum intensity) and 1.0 (maximum intensity).

r g b

rg

Same as RG but used for nonstroking operations.

c m y k

K

Set the stroking colour space to DeviceCMYK (or the DefaultCMYK

colour space; see 8.6.5.6, "Default Colour Spaces") and set the colour to

use for stroking operations. Each operand shall be a number between 0.0

(zero concentration) and 1.0 (maximum concentration). The behaviour of

this operator is affected by the overprint mode (see 8.6.7, "Overprint

Control").

c m y k

k

Same as K but used for nonstroking operations.

Invoking operators that specify colours or other colour-related parameters in the graphics state is restricted in

certain circumstances. This restriction occurs when defining graphical figures whose colours shall be specified

separately each time they are used. Specifically, the restriction applies in these circumstances:

•

In any glyph description that uses the d1 operator (see 9.6.5, "Type 3 Fonts")

•

In the content stream of an uncoloured tiling pattern (see 8.7.3.3, "Uncoloured Tiling Patterns")

172

8.7.2

General Properties of Patterns

A pattern dictionary contains descriptive information defining the appearance and properties of a pattern. All

pattern dictionaries shall contain an entry named PatternType, whose value identifies the kind of pattern the

dictionary describes: type 1 for a tiling pattern or type 2 for a shading pattern. The remaining contents of the

dictionary depend on the pattern type and are detailed in the sub-clauses on individual pattern types.

All patterns shall be treated as colours; a Pattern colour space shall be established with the CS or cs operator

just like other colour spaces, and a particular pattern shall be installed as the current colour with the SCN or

scn operator (see Table 74).

A pattern’s appearance is described with respect to its own internal coordinate system. Every pattern has a

pattern matrix, a transformation matrix that maps the pattern’s internal coordinate system to the default

coordinate system of the pattern’s parent content stream (the content stream in which the pattern is defined as

a resource). The concatenation of the pattern matrix with that of the parent content stream establishes the

pattern coordinate space, within which all graphics objects in the pattern shall be interpreted.

NOTE 1

If a pattern is used on a page, the pattern appears in the Pattern subdictionary of that page’s resource

dictionary, and the pattern matrix maps pattern space to the default (initial) coordinate space of the page.

Changes to the page’s transformation matrix that occur within the page’s content stream, such as rotation and

scaling, have no effect on the pattern; it maintains its original relationship to the page no matter where on the

page it is used. Similarly, if a pattern is used within a form XObject (see 8.10, "Form XObjects"), the pattern

matrix maps pattern space to the form’s default user space (that is, the form coordinate space at the time the

form is painted with the Do operator). A pattern may be used within another pattern; the inner pattern’s matrix

defines its relationship to the pattern space of the outer pattern.

NOTE 2

PostScript allows a pattern to be defined in one context but used in another. For example, a pattern might be

defined on a page (that is, its pattern matrix maps the pattern coordinate space to the user space of the page)

but be used in a form on that page, so that its relationship to the page is independent of each individual

placement of the form. PDF does not support this feature; in PDF, all patterns shall be local to the context in

which they are defined.

8.7.3

Tiling Patterns

8.7.3.1

General

A tiling pattern consists of a small graphical figure called a pattern cell. Painting with the pattern replicates the

cell at fixed horizontal and vertical intervals to fill an area. The effect is as if the figure were painted on the

surface of a clear glass tile, identical copies of which were then laid down in an array covering the area and

trimmed to its boundaries. This process is called tiling the area.

The pattern cell can include graphical elements such as filled areas, text, and sampled images. Its shape need

not be rectangular, and the spacing of tiles can differ from the dimensions of the cell itself. When performing

painting operations such as S (stroke) or f (fill), the conforming reader shall paint the cell on the current page as

many times as necessary to fill an area. The order in which individual tiles (instances of the cell) are painted is

unspecified and unpredictable; figures on adjacent tiles should not overlap.

The appearance of the pattern cell shall be defined by a content stream containing the painting operators

needed to paint one instance of the cell. Besides the usual entries common to all streams (see Table 5), this

stream’s dictionary may contain the additional entries listed in Table 75.

Table 75 - Additional Entries Specific to a Type 1 Pattern Dictionary

Key

Type

Value

Type

name

(Optional) The type of PDF object that this dictionary describes; if

present, shall be Pattern for a pattern dictionary.

PatternType

integer

(Required) A code identifying the type of pattern that this dictionary

describes; shall be 1 for a tiling pattern.

174

Table 75 - Additional Entries Specific to a Type 1 Pattern Dictionary (continued)

Key

Type

Value

PaintType

integer

(Required) A code that determines how the colour of the pattern cell

shall be specified:

a) Coloured tiling pattern. The pattern’s content stream shall specify

the colours used to paint the pattern cell. When the content

stream begins execution, the current colour is the one that was

initially in effect in the pattern’s parent content stream. This is

similar to the definition of the pattern matrix; see 8.7.2, "General

Properties of Patterns".

b) Uncoloured tiling pattern. The pattern’s content stream shall not

specify any colour information. Instead, the entire pattern cell is

painted with a separately specified colour each time the pattern is

used. Essentially, the content stream describes a stencil through

which the current colour shall be poured. The content stream

shall not invoke operators that specify colours or other colour-

related parameters in the graphics state; otherwise, an error

occurs (see 8.6.8, "Colour Operators"). The content stream may

paint an image mask, however, since it does not specify any

colour information (see 8.9.6.2, "Stencil Masking").

TilingType

integer

(Required) A code that controls adjustments to the spacing of tiles

relative to the device pixel grid:

a) Constant spacing. Pattern cells shall be spaced

consistently—that is, by a multiple of a device pixel. To achieve

this, the conforming reader may need to distort the pattern cell

slightly by making small adjustments to XStep, YStep, and the

transformation matrix. The amount of distortion shall not exceed 1

device pixel.

b) No distortion. The pattern cell shall not be distorted, but the

spacing between pattern cells may vary by as much as 1 device

pixel, both horizontally and vertically, when the pattern is painted.

This achieves the spacing requested by XStep and YStep on

average but not necessarily for each individual pattern cell.

c) Constant spacing and faster tiling. Pattern cells shall be spaced

consistently as in tiling type

1 but with additional distortion

permitted to enable a more efficient implementation.

BBox

rectangle

(Required) An array of four numbers in the pattern coordinate system

giving the coordinates of the left, bottom, right, and top edges,

respectively, of the pattern cell’s bounding box. These boundaries

shall be used to clip the pattern cell.

XStep

number

(Required) The desired horizontal spacing between pattern cells,

measured in the pattern coordinate system.

YStep

number

(Required) The desired vertical spacing between pattern cells,

measured in the pattern coordinate system.

NOTE

XStep and YStep may differ from the dimensions of the

pattern cell implied by the BBox entry. This allows tiling

with irregularly shaped figures.

XStep and YStep may be either positive or negative but shall not be

zero.

Resources

dictionary

(Required) A resource dictionary that shall contain all of the named

resources required by the pattern’s content stream

(see

7.8.3,

"Resource Dictionaries").

Matrix

array

(Optional) An array of six numbers specifying the pattern matrix (see

8.7.2, "General Properties of Patterns"). Default value: the identity

matrix [ 1 0 0 1 0 0 ].

175

0.5 0.2 1.0 /P1 scn

% Change nonstroking colour

50 50 m

% Start new path

175 50 l

% Construct triangular path

112.5 158.253 l

b

% Close, fill, and stroke path

endstream

endobj

8.7.4

Shading Patterns

8.7.4.1

General

Shading patterns (PDF 1.3) provide a smooth transition between colours across an area to be painted,

independent of the resolution of any particular output device and without specifying the number of steps in the

colour transition. Patterns of this type shall be described by pattern dictionaries with a pattern type of 2.

Table 76 shows the contents of this type of dictionary.

Table 76 - Entries in a Type 2 Pattern Dictionary

Key

Type

Value

Type

name

(Optional) The type of PDF object that this dictionary describes; if

present, shall be Pattern for a pattern dictionary.

PatternType

integer

(Required) A code identifying the type of pattern that this dictionary

describes; shall be 2 for a shading pattern.

Shading

dictionary

(Required) A shading object (see below) defining the shading pattern’s

or stream

gradient fill. The contents of the dictionary shall consist of the entries in

Table 78 and those in one of Tables 79 to 84.

Matrix

array

(Optional) An array of six numbers specifying the pattern matrix (see

8.7.2, "General Properties of Patterns"). Default value: the identity

matrix [ 1 0 0 1 0 0 ].

ExtGState

dictionary

(Optional) A graphics state parameter dictionary (see 8.4.5, "Graphics

State Parameter Dictionaries") containing graphics state parameters to

be put into effect temporarily while the shading pattern is painted. Any

parameters that are so specified shall be inherited from the graphics

state that was in effect at the beginning of the content stream in which

the pattern is defined as a resource.

The most significant entry is Shading, whose value shall be a shading object defining the properties of the

shading pattern’s gradient fill. This is a complex “paint” that determines the type of colour transition the shading

pattern produces when painted across an area. A shading object shall be a dictionary or a stream, depending

on the type of shading; the term shading dictionary is used generically throughout this sub-clause to refer to

either a dictionary object or the dictionary portion of a stream object. (Those shading objects that are streams

are specifically identified as such in the descriptions of particular shading types; unless otherwise stated, they

are understood to be simple dictionaries instead.)

By setting a shading pattern as the current colour in the graphics state, a PDF content stream may use it with

painting operators such as f (fill), S (stroke), Tj (show text), or Do (paint external object) with an image mask to

paint a path, character glyph, or mask with a smooth colour transition. When a shading is used in this way, the

geometry of the gradient fill is independent of that of the object being painted.

8.7.4.2

Shading Operator

When the area to be painted is a relatively simple shape whose geometry is the same as that of the gradient fill

itself, the sh operator may be used instead of the usual painting operators. sh accepts a shading dictionary as

an operand and applies the corresponding gradient fill directly to current user space. This operator does not

181

require the creation of a pattern dictionary or a path and works without reference to the current colour in the

graphics state. Table 77 describes the sh operator.

NOTE

Patterns defined by type 2 pattern dictionaries do not tile. To create a tiling pattern containing a gradient fill,

invoke the sh operator from within the content stream of a type 1 (tiling) pattern.

Table 77 - Shading Operator

Operands

Operator

Description

name

sh

(PDF 1.3) Paint the shape and colour shading described by a shading

dictionary, subject to the current clipping path. The current colour in the

graphics state is neither used nor altered. The effect is different from that of

painting a path using a shading pattern as the current colour.

name is the name of a shading dictionary resource in the Shading

subdictionary of the current resource dictionary

(see

7.8.3, "Resource

Dictionaries"). All coordinates in the shading dictionary are interpreted

relative to the current user space. (By contrast, when a shading dictionary is

used in a type 2 pattern, the coordinates are expressed in pattern space.) All

colours are interpreted in the colour space identified by the shading

dictionary’s ColorSpace entry (see Table 78). The Background entry, if

present, is ignored.

This operator should be applied only to bounded or geometrically defined

shadings. If applied to an unbounded shading, it paints the shading’s

gradient fill across the entire clipping region, which may be time-consuming.

8.7.4.3

Shading Dictionaries

A shading dictionary specifies details of a particular gradient fill, including the type of shading to be used, the

geometry of the area to be shaded, and the geometry of the gradient fill. Various shading types are available,

depending on the value of the dictionary’s ShadingType entry:

•

Function-based shadings (type 1) define the colour of every point in the domain using a mathematical

function (not necessarily smooth or continuous).

•

Axial shadings (type 2) define a colour blend along a line between two points, optionally extended beyond

the boundary points by continuing the boundary colours.

•

Radial shadings (type 3) define a blend between two circles, optionally extended beyond the boundary

circles by continuing the boundary colours. This type of shading is commonly used to represent three-

dimensional spheres and cones.

•

Free-form Gouraud-shaded triangle meshes (type 4) define a common construct used by many three-

dimensional applications to represent complex coloured and shaded shapes. Vertices are specified in free-

form geometry.

•

Lattice-form Gouraud-shaded triangle meshes (type 5) are based on the same geometrical construct as

type 4 but with vertices specified as a pseudorectangular lattice.

•

Coons patch meshes (type 6) construct a shading from one or more colour patches, each bounded by four

cubic Bézier curves.

•

Tensor-product patch meshes (type 7) are similar to type 6 but with additional control points in each patch,

affording greater control over colour mapping.

NOTE 1

Table 78 shows the entries that all shading dictionaries share in common; entries specific to particular shading

types are described in the relevant sub-clause.

NOTE 2

The term target coordinate space, used in many of the following descriptions, refers to the coordinate space

into which a shading is painted. For shadings used with a type 2 pattern dictionary, this is the pattern

182

coordinate space, discussed in 8.7.2, "General Properties of Patterns". For shadings used directly with the sh

operator, it is the current user space.

Table 78 - Entries Common to All Shading Dictionaries

Key

Type

Value

ShadingType

integer

(Required) The shading type:

1 Function-based shading

2 Axial shading

3 Radial shading

4 Free-form Gouraud-shaded triangle mesh

5 Lattice-form Gouraud-shaded triangle mesh

6 Coons patch mesh

7 Tensor-product patch mesh

ColorSpace

name or

(Required) The colour space in which colour values shall be

array

expressed. This may be any device, CIE-based, or special colour

space except a Pattern space. See 8.7.4.4, "Colour Space: Special

Considerations" for further information.

Background

array

(Optional) An array of colour components appropriate to the colour

space, specifying a single background colour value. If present, this

colour shall be used, before any painting operation involving the

shading, to fill those portions of the area to be painted that lie outside

the bounds of the shading object.

NOTE

In the opaque imaging model, the effect is as if the

painting operation were performed twice: first with the

background colour and then with the shading.

NOTE

The background colour is applied only when the shading

is used as part of a shading pattern, not when it is painted

directly with the sh operator.

BBox

rectangle

(Optional) An array of four numbers giving the left, bottom, right, and

top coordinates, respectively, of the shading’s bounding box. The

coordinates shall be interpreted in the shading’s target coordinate

space. If present, this bounding box shall be applied as a temporary

clipping boundary when the shading is painted, in addition to the

current clipping path and any other clipping boundaries in effect at that

time.

AntiAlias

boolean

(Optional) A flag indicating whether to filter the shading function to

prevent aliasing artifacts.

NOTE

The shading operators sample shading functions at a rate

determined by the resolution of the output device.

Aliasing can occur if the function is not smooth—that is, if

it has a high spatial frequency relative to the sampling

rate. Anti-aliasing can be computationally expensive and

is usually unnecessary, since most shading functions are

smooth enough or are sampled at a high enough

frequency to avoid aliasing effects. Anti-aliasing may not

be implemented on some output devices, in which case

this flag is ignored.

Default value: false.

Shading types 4 to 7 shall be defined by a stream containing descriptive data characterizing the shading’s

gradient fill. In these cases, the shading dictionary is also a stream dictionary and may contain any of the

standard entries common to all streams (see Table 5). In particular, shall include a Length entry.

In addition, some shading dictionaries also include a Function entry whose value shall be a function object

(dictionary or stream) defining how colours vary across the area to be shaded. In such cases, the shading

183

continuous range of colours. For similar reasons, an Indexed colour space shall not be used in any

shading whose colour values are generated by a function; this rule applies to any shading dictionary that

contains a Function entry.

8.7.4.5

Shading Types

8.7.4.5.1 General

In addition to the entries listed in Table 78, all shading dictionaries have entries specific to the type of shading

they represent, as indicated by the value of their ShadingType entry. The following sub-clauses describe the

available shading types and the dictionary entries specific to each.

8.7.4.5.2 Type 1 (Function-Based) Shadings

In Type 1 (function-based) shadings, the colour at every point in the domain is defined by a specified

mathematical function. The function need not be smooth or continuous. This type is the most general of the

available shading types and is useful for shadings that cannot be adequately described with any of the other

types. Table 79 shows the shading dictionary entries specific to this type of shading, in addition to those

common to all shading dictionaries (see Table 78).

This type of shading shall not be used with an Indexed colour space.

Table 79 - Additional Entries Specific to a Type 1 Shading Dictionary

Key

Type

Value

Domain

array

(Optional) An array of four numbers [ x_min x_max y_min y_max ] specifying

the rectangular domain of coordinates over which the colour function(s)

are defined. Default value: [ 0.0 1.0

0.0 1.0 ].

Matrix

array

(Optional) An array of six numbers specifying a transformation matrix

mapping the coordinate space specified by the Domain entry into the

shading’s target coordinate space.

NOTE

To map the domain rectangle [ 0.0 1.0

0.0 1.0 ] to a 1-inch

square with lower-left corner at coordinates (100, 100) in

default user space, the Matrix value would be

[72

0 0 72 100 100 ].

Default value: the identity matrix [ 1

0 0 1 0 0 ].

Function

function

(Required) A 2-in, n-out function or an array of n 2-in, 1-out functions

(where n is the number of colour components in the shading dictionary’s

colour space). Each function’s domain shall be a superset of that of the

shading dictionary. If the value returned by the function for a given colour

component is out of range, it shall be adjusted to the nearest valid value.

The domain rectangle (Domain) establishes an internal coordinate space for the shading that is independent of

the target coordinate space in which it shall be painted. The colour function(s) (Function) specify the colour of

the shading at each point within this domain rectangle. The transformation matrix (Matrix) then maps the

domain rectangle into a corresponding rectangle or parallelogram in the target coordinate space. Points within

the shading’s bounding box (BBox) that fall outside this transformed domain rectangle shall be painted with the

shading’s background colour (Background); if the shading dictionary has no Background entry, such points

shall be left unpainted. If the function is undefined at any point within the declared domain rectangle, an error

may occur, even if the corresponding transformed point falls outside the shading’s bounding box.

8.7.4.5.3 Type 2 (Axial) Shadings

Type 2 (axial) shadings define a colour blend that varies along a linear axis between two endpoints and extends

indefinitely perpendicular to that axis. The shading may optionally be extended beyond either or both endpoints

185

by continuing the boundary colours indefinitely. Table 80 shows the shading dictionary entries specific to this

type of shading, in addition to those common to all shading dictionaries (see Table 78).

This type of shading shall not be used with an Indexed colour space.

Table 80 - Additional Entries Specific to a Type 2 Shading Dictionary

Key

Type

Value

Coords

array

(Required) An array of four numbers [ x₀ y₀ x₁ y₁ ] specifying the starting

and ending coordinates of the axis, expressed in the shading’s target

coordinate space.

Domain

array

(Optional) An array of two numbers [ t₀ t₁ ] specifying the limiting values of

a parametric variable t. The variable is considered to vary linearly

between these two values as the colour gradient varies between the

starting and ending points of the axis. The variable t becomes the input

argument to the colour function(s). Default value: [ 0.0 1.0 ].

Function

function

(Required) A 1-in, n-out function or an array of n 1-in, 1-out functions

(where n is the number of colour components in the shading dictionary’s

colour space). The function(s) shall be called with values of the

parametric variable t in the domain defined by the Domain entry. Each

function’s domain shall be a superset of that of the shading dictionary. If

the value returned by the function for a given colour component is out of

range, it shall be adjusted to the nearest valid value.

Extend

array

(Optional) An array of two boolean values specifying whether to extend

the shading beyond the starting and ending points of the axis,

respectively. Default value: [ false false ].

The colour blend shall be accomplished by linearly mapping each point (x, y) along the axis between the

endpoints (x₀ , y₀ ) and (x₁ , y₁ ) to a corresponding point in the domain specified by the shading dictionary’s

Domain entry. The points (0, 0) and (1, 0) in the domain correspond respectively to (x₀ , y₀ ) and (x₁ , y₁ ) on the

axis. Since all points along a line in domain space perpendicular to the line from (0, 0) to (1, 0) have the same

colour, only the new value of x needs to be computed:

(

x₁

-

x₀

)

×

(

x x₀

)

+

(

y₁

-

y₀

)

×

(

y y₀

)

x′

= ------------------------------------------------------------------------------------------------------

(x

-

x₀

)²

+

(

y₁

-

y₀

)²

1

The value of the parametric variable t is then determined from x ¢ as follows:

•

For 0

£ x ¢ £ 1, t = t₀ + (t₁ - t₀ )

¥ x ¢.

•

For x ¢ < 0, if the first element of the Extend array is true, then t = t₀ ; otherwise, t is undefined and the

point shall be left unpainted.

•

For x ¢ > 1, if the second element of the Extend array is true, then t = t₁ ; otherwise, t is undefined and the

point shall be left unpainted.

The resulting value of t shall be passed as input to the function(s) defined by the shading dictionary’s Function

entry, yielding the component values of the colour with which to paint the point (x, y).

NOTE

Figure L.10 in Annex L shows three examples of the use of an axial shading to fill a rectangle and display text.

The area to be filled extends beyond the shading’s bounding box. The shading is the same in all three cases,

except for the values of the Background and Extend entries in the shading dictionary. In the first example, the

shading is not extended at either end and no background colour is specified; therefore, the shading is clipped

to its bounding box at both ends. The second example still has no background colour specified, but the

shading is extended at both ends; the result is to fill the remaining portions of the filled area with the colours

186

defined at the ends of the shading. In the third example, the shading is extended at both ends and a

background colour is specified; therefore, the background colour is used for the portions of the filled area

beyond the ends of the shading.

8.7.4.5.4 Type 3 (Radial) Shadings

Type 3 (radial) shadings define a colour blend that varies between two circles. Shadings of this type are

commonly used to depict three-dimensional spheres and cones. Shading dictionaries for this type of shading

contain the entries shown in Table 81, as well as those common to all shading dictionaries (see Table 78).

This type of shading shall not be used with an Indexed colour space.

Table 81 - Additional Entries Specific to a Type 3 Shading Dictionary

Key

Type

Value

Coords

array

(Required) An array of six numbers

[x₀ y₀ r₀ x₁ y₁ r₁ ] specifying the

centres and radii of the starting and ending circles, expressed in the

shading’s target coordinate space. The radii r₀ and r₁ shall both be

greater than or equal to 0. If one radius is 0, the corresponding circle shall

be treated as a point; if both are 0, nothing shall be painted.

Domain

array

(Optional) An array of two numbers [ t₀ t₁ ] specifying the limiting values of

a parametric variable t. The variable is considered to vary linearly

between these two values as the colour gradient varies between the

starting and ending circles. The variable t becomes the input argument to

the colour function(s). Default value: [ 0.0

1.0 ].

Function

function

(Required) A 1-in, n-out function or an array of n 1-in, 1-out functions

(where n is the number of colour components in the shading dictionary’s

colour space). The function(s) shall be called with values of the

parametric variable t in the domain defined by the shading dictionary’s

Domain entry. Each function’s domain shall be a superset of that of the

shading dictionary. If the value returned by the function for a given colour

component is out of range, it shall be adjusted to the nearest valid value.

Extend

array

(Optional) An array of two boolean values specifying whether to extend

the shading beyond the starting and ending circles, respectively. Default

value: [ false false ].

The colour blend is based on a family of blend circles interpolated between the starting and ending circles that

shall be defined by the shading dictionary’s Coords entry. The blend circles shall be defined in terms of a

subsidiary parametric variable

t

-

t₀

s

= --------------

t

-

t₀

1

which varies linearly between 0.0 and 1.0 as t varies across the domain from t₀ to t₁ , as specified by the

dictionary’s Domain entry. The centre and radius of each blend circle shall be given by the following parametric

equations:

x_c(s)

=

x₀

+

s

×

(

x₁

–

x₀

)

y_c(s)

=

y₀

+

s

×

(

y₁

–

y₀

)

r(s)

=

r₀

+

s

×

(

r₁

–

r₀

)

Each value of s between 0.0 and 1.0 determines a corresponding value of t, which is passed as the input

argument to the function(s) defined by the shading dictionary’s Function entry. This yields the component

values of the colour with which to fill the corresponding blend circle. For values of s not lying between 0.0 and

187

12 0 obj

% Second subfunction

<<

/FunctionType 2

/Domain [ 0.0 1.0 ]

/C0 [ 0.929 0.357 1.000 0.298 ]

/C1 [ 0.941 0.400 1.000 0.102 ]

/N 1.374

>>

endobj

EXAMPLE 2

This example shows how each leaf shown in Figure L.14 in Annex L is drawn as a path and then filled

with the shading (where the name Sh1 is associated with object 5 by the Shading subdictionary of the

current resource dictionary; see 7.8.3, "Resource Dictionaries").

316.789 140.311 m

% Move to start of leaf

303.222 146.388 282.966 136.518 279.122 121.983 c

% Curved segment

277.322 120.182 l

% Straight line

285.125 122.688 291.441 121.716 298.156 119.386 c

% Curved segment

336.448 119.386 l

% Straight line

331.072 128.643 323.346 137.376 316.789 140.311 c

% Curved segment

W n

% Set clipping path

q

% Save graphics state

27.7843 0.0000 0.0000 -27.7843 310.2461 121.1521 cm

% Set matrix

/Sh1 sh

% Paint shading

Q

% Restore graphics state

8.7.4.5.5 Type 4 Shadings (Free-Form Gouraud-Shaded Triangle Meshes)

Type 4 shadings (free-form Gouraud-shaded triangle meshes) are commonly used to represent complex

coloured and shaded three-dimensional shapes. The area to be shaded is defined by a path composed entirely

of triangles. The colour at each vertex of the triangles is specified, and a technique known as Gouraud

interpolation is used to colour the interiors. The interpolation functions defining the shading may be linear or

nonlinear. Table 82 shows the entries specific to this type of shading dictionary, in addition to those common to

all shading dictionaries (see Table 78) and stream dictionaries (see Table 5).

Table 82 - Additional Entries Specific to a Type 4 Shading Dictionary

Key

Type

Value

BitsPerCoordinate

integer

(Required) The number of bits used to represent each vertex

coordinate. The value shall be 1, 2, 4, 8, 12, 16, 24, or 32.

BitsPerComponent

integer

(Required) The number of bits used to represent each colour

component. The value shall be 1, 2, 4, 8, 12, or 16.

BitsPerFlag

integer

(Required) The number of bits used to represent the edge flag for

each vertex (see below). The value of BitsPerFlag shall be 2, 4, or

8, but only the least significant 2 bits in each flag value shall be

used. The value for the edge flag shall be 0, 1, or 2.

Decode

array

(Required) An array of numbers specifying how to map vertex

coordinates and colour components into the appropriate ranges of

values. The decoding method is similar to that used in image

dictionaries (see 8.9.5.2, "Decode Arrays"). The ranges shall be

specified as follows:

[x_min x_max y_min y_max c_1,min c_1,max

… c_n,min c_n,max ]

Only one pair of c values shall be specified if a Function entry is

present.

189

Table 82 - Additional Entries Specific to a Type 4 Shading Dictionary (continued)

Key

Type

Value

Function

function

(Optional) A 1-in, n-out function or an array of n 1-in, 1-out functions

(where n is the number of colour components in the shading

dictionary’s colour space). If this entry is present, the colour data for

each vertex shall be specified by a single parametric variable rather

than by n separate colour components. The designated function(s)

shall be called with each interpolated value of the parametric

variable to determine the actual colour at each point. Each input

value shall be forced into the range interval specified for the

corresponding colour component in the shading dictionary’s

Decode array. Each function’s domain shall be a superset of that

interval. If the value returned by the function for a given colour

component is out of range, it shall be adjusted to the nearest valid

value.

This entry shall not be used with an Indexed colour space.

Unlike shading types 1 to 3, types 4 to 7 shall be represented as streams. Each stream contains a sequence of

vertex coordinates and colour data that defines the triangle mesh. In a type 4 shading, each vertex is specified

by the following values, in the order shown:

f x y c₁… c_n

where

f is the vertex’s edge flag (discussed below)

x and y are its horizontal and vertical coordinates

c₁… c_n are its colour components

All vertex coordinates shall be expressed in the shading’s target coordinate space. If the shading dictionary

includes a Function entry, only a single parametric value, t, shall be specified for each vertex in place of the

colour components c₁… c_n .

The edge flag associated with each vertex determines the way it connects to the other vertices of the triangle

mesh. A vertex v_a with an edge flag value f_a = 0 begins a new triangle, unconnected to any other. At least two

more vertices (v_b and v_c ) shall be provided, but their edge flags shall be ignored. These three vertices define a

triangle (v_a , vb , vc ), as shown in Figure 24.

f_a=0

(Start new triangle)

Previous

v_a

triangle

v_b

v_c

Figure 24 - Starting a New Triangle in a Free-form Gouraud-shaded Triangle Mesh

190

Subsequent triangles shall be defined by a single new vertex combined with two vertices of the preceding

triangle. Given triangle (v_a , vb , vc ), where vertex v_a precedes vertex v_b in the data stream and v_b precedes v_c ,

a new vertex v_d can form a new triangle on side v_bc or side v_ac , as shown in Figure 25. (Side v_ab is assumed to

be shared with a preceding triangle and therefore is not available for continuing the mesh.) If the edge flag is

f_d = 1 (side vbc ), the next vertex forms the triangle (v_b , v_c , v_d ); if the edge flag is f_d = 2 (side v_ac ), the next

vertex forms the triangle (v_a , v_c , v_d ). An edge flag of f_d = 0 starts a new triangle, as described above.

f_d =0

f_d =1

f_d =2

v_a

v_a

v_a

v_d

One new

vertex

v_b

v_c

v_b

v_c

v_b

v_c

v_d

One new

Three new

vertex

v_d

vertices

v_e

v_f

Figure 25 - Connecting Triangles in a Free-form Gouraud-shaded Triangle Mesh

Complex shapes can be created by using the edge flags to control the edge on which subsequent triangles are

formed.

EXAMPLE

Figure 26 shows two simple examples. Mesh 1 begins with triangle 1 and uses the following edge flags to

draw each succeeding triangle:

1

(

f_a = f_b = f_c

=

0

)

7

(

f_i

=

2

)

2

(

f_d

=

1

)

8

(

f_j

=

2

)

3

(

f_e

=

1

)

9

(

f_k

=

2

)

4

(

f_f

=

1

)

10

(

f_l

=

1

)

5

(

f_g

=

1

)

11

(fm

=

1

)

6

(fh

=

1

)

Mesh 2 again begins with triangle 1 and uses the following edge flags:

1

(

f_a = f_b = f_c

=

0

)

4

(

f_f

=

2

)

2

(

f_d

=

1

)

5

(

f_g

=

2

)

3

(

f_e

=

2

)

6

(

f_h

=

2

)

The stream shall provide vertex data for a whole number of triangles with appropriate edge flags; otherwise, an

error occurs.

191

v_a

v_c

v_e

v_g

v_a

v_c

v_h

v_h = v_a

1

3

5

1

2

v_d

4

v_f

6

6

v_b

2

v_b

v_h

v_g

v_d

v_m

v_k

11

9

7

5

3

v_m = v_b

10

8

4

v_l

v_j

v_i

v_f

v_e

v_k = v_d

Mesh 1

Mesh 2

Figure 26 - Varying the Value of the Edge Flag to Create Different Shapes

The data for each vertex consists of the following items, reading in sequence from higher-order to lower-order

bit positions:

•

An edge flag, expressed in BitsPerFlag bits

•

A pair of horizontal and vertical coordinates, expressed in BitsPerCoordinate bits each

•

A set of n colour components (where n is the number of components in the shading’s colour space),

expressed in BitsPerComponent bits each, in the order expected by the sc operator

Each set of vertex data shall occupy a whole number of bytes. If the total number of bits required is not divisible

by 8, the last data byte for each vertex is padded at the end with extra bits, which shall be ignored. The

coordinates and colour values shall be decoded according to the Decode array in the same way as in an image

dictionary (see 8.9.5.2, "Decode Arrays").

If the shading dictionary contains a Function entry, the colour data for each vertex shall be specified by a

single parametric value t rather than by n separate colour components. All linear interpolation within the triangle

mesh shall be done using the t values. After interpolation, the results shall be passed to the function(s)

specified in the Function entry to determine the colour at each point.

8.7.4.5.6 Type 5 Shadings (Lattice-Form Gouraud-Shaded Triangle Meshes)

Type 5 shadings (lattice-form Gouraud-shaded triangle meshes) are similar to type 4, but instead of using free-

form geometry, their vertices are arranged in a pseudorectangular lattice, which is topologically equivalent to a

rectangular grid. The vertices are organized into rows, which need not be geometrically linear (see Figure 27).

(i, j)

(i, j+1)

(i+1, j)

(i+1, j+1)

Ideal lattice

Pseudorectangular lattice

Figure 27 - Lattice-form Triangle Meshes

192

Content      ..     3      4      5      6     ..