Abstract
This Working Draft is a primer for use of the Scalable Vector Graphics (SVG) Language
for color managed workflows. It explains the technical background and gives guidelines
on how to use the SVG Color specification with SVG 1.2 Tiny and SVG 1.2 Full modules.
It is purely informative and has no conformance statements.
Status of This Document
This section describes the status of this document at the time of its publication.
Other documents may supersede this document. A list of current W3C publications
and the latest revision of this technical report can be found in the
W3C technical reports index at http://www.w3.org/TR/.
This document is a First Public Working Draft. It defines features of SVG specific to color management.
It is a draft in progress; some descriptions in this document may be incomplete.
This document shows the current thoughts of the SVG Working Group on the use of
SVG for printing and should not yet be considered stable. There is an accompanying
SVG Color 1.2, Part 2: Language that lists the ways
SVG Color may be used.
This document has been produced by the W3C
SVG Working Group as part of the W3C
Graphics Activity within the Interaction
Domain. The Working Group expects to advance this Working Draft to Recommendation
Status.
We explicitly invite comments on this specification. Please send them to
[email protected] (archives).
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Publication as a Working Draft does not imply endorsement by the
W3C Membership. This is a draft document and may be updated, replaced
or obsoleted by other documents at any time. It is inappropriate to cite this document
as other than work in progress.
This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. This document is informative only. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.
How to read this document and give feedback
The main purpose of this document is to encourage public feedback. The best way
to give feedback is by sending an email to
[email protected]. Please identify in the subject line of your message
the part of the specificationto which your comment refers (e.g "Print compositing"
or "Print render formats"). If you have comments on multiple areas of this document,
then it is preferable to send several separate comments.
The public are welcome to comment on any aspect in this document, but there are
a few areas in which the SVG Working Group are explicitly requesting feedback. These
areas are noted in place within this document like this.
Table of Contents
1
Introduction
Because of its scalable, geometric nature, SVG is inherently suited to both print
and screen output. The same colors can be output, using an ICC-based color managed
workflow on the printer and an sRGB fallback approximation on screen. This has been
true since SVG 1.0, and so SVG has been used in print workflows (for example, in
combination with XSL FO) as well as on screen.
It is common in cross-media publishing to design content which will be used both
online and in print media. This specification gives guidance on how to create such
content and how to indicate that it has been adapted to improve its color capability.
2
Color specification
SVG Color allows color to be specified in a number of ways. All of the sRGB color
syntaxes from SVG Print 1.2 are supported. The ICC-based color syntax from SVG 1.1
Full is also supported, and unlike SVG 1.1 rendering this feature is not optional. New to the SVG Color specification, ICC named
colors and device colors are supported as well: their
syntax is defined below.
2.1
sRGB colors
As with SVG Tiny 1.2, colors may be specified in the sRGB colorspace without providing
a color profile. This color space, which uuses the chromaticities of a standard
TV broadcast monitor and viewing conditions typical of an office environment, has
a reduced gamut suitable for minimising banding on 'real world' colors at the expense
of being unable to directly represent highly saturated colors. A number of equivalent
syntactic forms are supported, as
defined in SVG Tiny 1.2:
<circle cx="200" cy="135" r="20" fill="#3b3"/>
<circle cx="240" cy="135" r="20" fill="#33bb33"/>
<circle cx="200" cy="175" r="20" fill="rgb(51,187,51)"/>
<circle cx="240" cy="175" r="20" fill="rgb(20%,73.333%,20%)"/>
2.2
ICC colors
Since SVG 1.0, SVG has contained functionality for use of ICC color profiles which
define colors in a different color space than sRGB. This functionality has been
available since SVG 1.0 but for the most part has not been well understood. SVP
Print tightens the conformance criteria for using ICC colors.
For example, it is possible to specify all objects in terms of an ICC color space
such as SWOP CMYK and the SVG renderer perform all rendering of the objects entirely
in the SWOP CMYK space followed by color correction for a printer target CMYK. This
render workflow would never require conversion into and out of sRGB.
In the case where opacity is used and objects overlap a render device must use the
supplied sRGB fallback color in order to composite objects together.
The implication of this is that it is possible to use a fully colormanaged workflow (using
SVG 1.0 onwards) that supports a full CMYK pipeline via the use of ICC profiles.
Such an SVG render device must also be capable of handling a switch into the fallback
render color space (sRGB) for the overlapping portions of objects with transparency.
An implementation may determine the areas of an object to render in object's ICC
color and those areas to render in its sRGB fallback by doing object intersection
calculations as a pre-render step. An implementation could alternatviely decide
render color choice on a pixel by pixel basis during rasterisation. Such behaviour
is implementation specific and can lead to varying rendering results from different
implementations at the borders of overlapping areas when using ICC colors.
2.3
Named color
SVG Color introduces the ability to use so-called 'named' or 'spot' colors. Named
colors are used in many print applications and are supported in SVG Print through
the use of ICC named color profiles. For color managed displays, the desired color may be accurately simulated. Non color managed user agents will use the sRGB fallback value.
2.3.1
Use of the ICC named color syntax
The paint specifiers for fill and stroke include the icc-named-color
keyword. This may be used to look up colors by their name. For example in graphic
arts workflows it is common to use Pantone®
color names for specifying paint on objects. The icc-named-color
keyword may be used for such workflows.
2.3.2
ICC named color profile management
An SVG 1.2 file may specify ICC named color profiles via use of the
color-profile element.
The ICC specification indicates that named color profiles must contain a PCS (Profile
Connection Space) representation and can optionally contain a device representation
for each named color. An implementation may support device representations of ICC
named colors, however that support is device specific and should be managed outside
of the SVG file itself by use of some form of job ticket information.
2.4
CIE LAB color specification
SVG Color allows any visible color to be directly specified in the standard,
device-independent CIE L*ab color space. Both the cartestian (L*ab)
and polar (L*CHab) forms are supported. The latter has the advantage that
chroma and hue are more intuitive to specify than the abstract a and b axes.
2.4
Device color specification
Occasionally, it is necessary to specify non-colormanaged colors in terms of the
eventual device colorants. An example would be the creation of registration marks,
or tint bars of pure ink for quality control purposes.
3
References
- CRC
- C.S. McCamy, H. Marcus, J.G. Davidson, “A Color-Rendition Chart,” J. Appl. Phot. Eng., Vol. 2, No. 3, Summer 1976, pp. 95-99, Society of Photographic Scientists and Engineers (now called “The Society for Imaging Science and Technology (IS&T)”)
- SVG12
-
Scalable Vector Graphics (SVG) 1.2 Specification, Dean Jackson
editor, W3C, 27 October 2004 (Working Draft). See
http://www.w3.org/TR/2004/WD-SVG12-20041027/
- SVG12Reqs
-
SVG 1.1/1.2/2.0 Requirements, Dean Jackson editor, W3C, 22 April
2002 (Working Draft). See
http://www.w3.org/TR/2002/WD-SVG2Reqs-20020422/
- [SVGColor]
- SVG Color ,
Chris Lilley, Anthony Grasso, eds. World Wide Web
Consortium, 01 October 2009.
Latest version available at: http://www.w3.org/TR/SVGColor12