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Vector Images#

Edited by Kieron Niven#

Section 1: Introduction to Vector Images#

Section 2: Creating Vector Images#

Section 3: Archiving Vector Images#

Bibliography and Further Reading#


3.1 Deciding what to archive

      • Selection and retention
      • preservation intervention points / file and data lifecycles (specific to guide, will also be covered generically)

3.2deciding how to archive

      • archiving strategies (migration (to new format, to 'basic' format), emulation, refreshment)?
      • significant properties
      • file types

JISC Digital Preservation Programme: Study on the Significant Properties of Vector Images

All from AHDS Guide

Significant Characteristics

Vector graphics programmes are often used as a convenience for creating high quality line drawings or illustrations and represent a final product or the source for a hardcopy version. When this is the case then a bitmap version will probably be suitable for preservation and the depositor should be asked to export the graphic to a suitable format and size (see the Bitmap (raster) image Preservation Handbook).

Illustrator files will probably have been created as page illustrations and therefore a tiff (or png) export of the file will be an adequate format for preservation, and jpeg or png suitable for presentation. If the vector content is significant then the files should be converted to svg. Illustrator files .cdr is a proprietary format and not suitable for preservation. CorelDraw files will probably have been created as page illustrations and therefore a tiff (or png) export of the file will be an adequate format for preservation, and jpeg or png suitable for presentation. Ideally the depositor should create these files. If the vector content is significant then the files should be converted to svg or, if the drawing is layered, dxf.

In many cases the image is unlikely to have been created in isolation but as an illustration associated with some text. It is important that the document(s) the image is associated with is recorded plus the location within that document to which it relates. The caption or a description of the contents and purpose of the image is also important. Any meaning incorporated into conventions used in the drawing must be explained, i.e. the significance of colours, layers (including invisible layers), object types, line styles, line weights, text styles, fill and hatch styles, dimension styles.

Scripts

Images (e.g. Illustrator files) can contain scripts in AppleScript/OSA, JavaScript or VBScript. These scripts are aids to editing the document and hence do not add to the meaning so should be discarded.

Technique Check the graphic for hidden information (invisible layers, etc.) and the relevance or suitability of this material for archiving, i.e. does it consist of construction lines, text paths, etc., does the depositor have copyright.

Ensure that any linked data (e.g. other image files, fonts) are present. These should be embedded into the graphic.

If necessary export the graphic to a suitable archive format(s). This may be dependant on the nature of original, whether pure vector or vector and raster data. Mixed formats may require the separation of the vector and raster data. DXF is generally a good preservation medium for the vector content. Use a suitable preservation format for the raster content (see the Bitmap (raster) image Preservation Handbook). It may be possible to archive mixed content as SVG. Vector data should be archived at a suitable level of precision, preferably that used when collecting the original data. Exporting to an excessively low level of precision will degrade the data. Exporting to an excessively high level of precision will cause file bloat and may imply a false degree of precision for the data.

Validation of Exported Data There is no objective way to compare the original file and an exported version. The best that can be done is to use programmes that can be trusted to give an accurate rendering of each format, either to paper or screen, and to compare the results by eye.

Problems and Issues File migration to newer formats or to different packages can result in significant degradation of the image quality. This can be exacerbated, particularly if the migration is across platforms (e.g. from Mac to MS Windows), where the availability of fonts may differ. Programmes will usually substitute a font if the originally specified font cannot be found but the substitute may be inadequate and the resulting image spoiled.

3.3 Metadata and Documentation

      • project level
      • file level
      • standards specific to #

Relationship to other documents, caption

Level 1 (Essential) ?? Title or caption describing the graphic ?? Creator ?? Purpose ?? Relationship to other documents ?? Externally referenced files must be present ?? No embedded material for which the depositor does not hold copyright. Level 2 (Preferred) ?? Software and version used to create image/model ?? Creation/completion date ?? Explanation of all conventions used in the document (colours, layers, line styles, line weights, etc.) ?? Scale (i.e. what distance does a unit length of 1 represent). ?? Externally referenced material should be imported (bound) where possible. ?? Relevance of hidden material (in frozen / off / invisible layers)

3.4Structuring your archive

  • Copyright
    • specific copyright considerations for each guide.

  • Case study/studies

  • Check for any dependencies (linked files, object libraries, bitmaps, custom linestyles; shapes)

PDF as a possible dissemination format for 2D vector data. Means the user won't need any plug ins apart from the Adobe Acrobat reader 8.1