IHPDFProgressiveImageDecoder Interface

IHPDFProgressiveImageDecoder = interface
  ['{9C414FE8-9E8D-4A2B-B7F6-5AE4266138AE}']
  function DecodeNextScan(out ScanNumber: Integer):
    THPDFProgressiveImageDecodeStatus;
  function GetBitmap: TBitmap;
  function GetErrorMessage: AnsiString;
end;

Progressive decoding seam that yields one scan at a time so callers can paint intermediate images whilst decoding continues; DecodeNextScan reports progress through THPDFProgressiveImageDecodeStatus and the scan number it just completed

GetBitmap returns the current partially decoded bitmap and GetErrorMessage the reason for the last failure status

JPEG 2000 Progressive Decoding