THPDFJpegReducedDecoder

Decodes an encoded JPEG region straight into an exact low-resolution BGR24 bitmap

Declaration

function LoadFromBytes(const Data: THPDFJpegByteArray;
  const Region: TRect; TargetWidth, TargetHeight: Integer;
  MaxOutputBytes: Int64 = 268435456): Boolean;

function Decode: THPDFJpegReducedDecodeStatus;

Usage

Decoder := THPDFJpegReducedDecoder.Create;
try
  if Decoder.LoadFromBytes(Data, Rect(0, 0, 12000, 12000), 300, 300) and
    (Decoder.Decode = jrdsCompleted) then
  begin
    Bitmap.Assign(Decoder.Bitmap);
    Info := Decoder.Info;
  end;
finally
  Decoder.Free;
end;

Ownership and limits

• The decoder copies encoded input and owns the bitmap exposed by Bitmap
• The returned bitmap remains valid until the decoder is loaded again or destroyed
• MaxOutputBytes bounds the target bitmap and zero disables that explicit limit
• OnCancellationCheck is invoked from the scanline loop
• Info exposes decoder-reported scaled geometry and working-memory estimates

Related APIs

THPDFJpegReducedDecodeInfo · THPDFJpegReducedDecodeStatus · Reduced-DCT JPEG Decoding