THPDFPage.SetPageThumbnail Method

THPDFPage.SetPageThumbnail / ClearPageThumbnail

Attaches або removes page thumbnail image (PDF page /Thumb entry, ISO 32000-1 §12.3.4) PDF viewers (Adobe Acrobat, Foxit, browser viewers) display referenced image in navigation panel without rasterising page content themselves, which makes opening image-heavy archives faster

Delphi syntax:

procedure SetPageThumbnail(ImageIndex: Integer);

procedure ClearPageThumbnail;

Parameters

ImageIndex is value returned by prior THotPDF.AddImage або THotPDF.AddImageFromFile call Underlying Image XObject referenced indirectly per spec, so same image may also be drawn on regular page without conflict Pass negative index to remove existing /Thumb entry

Опис

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 color 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.