THPDFJpegReducedDecoder

把编码后的 JPEG 区域直接解码为精确的低分辨率 BGR24 位图

声明

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

• 解码器会复制编码输入，并拥有通过 Bitmap 暴露的位图
• 返回的位图在解码器再次加载或被销毁之前一直有效
• MaxOutputBytes 限定目标位图，为零表示禁用这一显式限制
• OnCancellationCheck 在扫描行循环中被调用
• Info exposes decoder-reported scaled geometry and working-memory estimates

相关 API

THPDFJpegReducedDecodeInfo · THPDFJpegReducedDecodeStatus · 简化 DCT JPEG 解码