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Attaches or removes a page thumbnail image (PDF page /Thumb entry, ISO 32000-1 §12.3.4). PDF viewers (Adobe Acrobat, Foxit, browser viewers) display the referenced image in their navigation panel without rasterising the page content themselves, which makes opening image-heavy archives noticeably faster.
Delphi syntax:
procedure SetPageThumbnail(ImageIndex: Integer);
procedure ClearPageThumbnail;
Parameters
ImageIndex is the value returned by a prior THotPDF.AddImage or THotPDF.AddImageFromFile call. The underlying Image XObject is referenced indirectly per the spec, so the same image may also be drawn on a regular page without conflict. Pass a negative index to remove an existing /Thumb entry.
Description
Each PDF page can carry an indirect reference to an Image XObject in its /Thumb key. The image is normally a downsampled 8-bit DeviceGray, DeviceRGB, or Indexed bitmap (Acrobat uses roughly one thumbnail point per page point), but HotPDF does not validate the colour space – the caller chooses what to attach. ClearPageThumbnail removes any previously attached thumbnail. SetPageThumbnail(-1) is equivalent to ClearPageThumbnail. Passing an ImageIndex that is not in range of the document’s image list raises a descriptive exception.
Example
PDF := THotPDF.Create(nil);
PDF.FileName := 'archive.pdf';
PDF.BeginDoc;
Idx := PDF.AddImageFromFile('preview.jpg', icJpeg);
PDF.CurrentPage.SetPageThumbnail(Idx);
PDF.EndDoc;
Availability
HotPDF v2.119.13. The PDF /Thumb entry is a PDF 1.0 feature and is not gated under PDF/A, PDF/X, or PDF/UA compliance modes. To make the viewer open with the thumbnail panel visible, also set THotPDF.PageMode := pmUseThumbs.
See also: Supported Image Formats, THPDFPage
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