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Alternative/Proxy

PDF/A version Conformance level Class type Severity
1, 2, 3 bua Conformance 5

The PDF/A document has alternative or proxy versions of an image, for example, a preview version in lower quality of an image.

Reproducibility

... Add Alternate image to an existing one. The alternate can be any other image object in the document.

  1. Create PDF with two images on canvas (for example in Adobe)
  2. Find object numbers for both images: /Page -> /Resources -> /XObject (for example - Image1=12 0 obj, Image2=13 0 obj)
  3. Create new object which will be used as /Alternate dictioanry
  4. Go to an object that describes the first image
  5. Add the key /Alternates (array type) with the link to object which was created at third step (e.g. /Alternates [15 0 R])
  6. Go to object which was created at third step
  7. Add the key /Image with link on the second image. This object would looks like 15 0 obj <</Image 13 0 R>> endobj
  8. Find Page content stream: /Page -> /Contents
  9. Go to page content stream
  10. Find operator which Invoke named XObject (second image) Note: name of the second image you can find in page resources dictionary
  11. Remove this operator from page content stream
  12. Update length of content stream, xref table and trailer

Reference

ISO 32000-1:2008, p. 212.