使用 ScanLine 交换红/蓝字节的快速方法

Question

目前，我循环 Canvas.Pixels[] 属性并读取画布上的每个像素以交换红色/蓝色字节（出于特定原因）。但是，每张图片平均需要 2 秒，而且我需要转换 8,000 多张图片（一夜之间）。我知道我可以使用ScanLine 的方法更快地完成这项工作，但我对ScanLine 一无所知 - 它的编码水平比我熟悉的要低得多。最快的方法是什么？我愿意等待一段时间来完成，但如果我能把这段时间切成两半或更多，那还是很好的。

现在，这是我使用的程序：

procedure SwapBytes(var Bmp: TBitmap);
var
  X, Y: Integer;
  R, G, B: Byte;
  C: TColor;
begin
  for Y := 0 to Bmp.Height - 1 do begin
    for X := 0 to Bmp.Width - 1 do begin
      C:= Bmp.Canvas.Pixels[X,Y];
      R:= GetRValue(C);
      G:= GetGValue(C);
      B:= GetBValue(C);
      Bmp.Canvas.Pixels[X,Y]:= RGB(B, G, R)
    end;
  end;
end;

补充说明：最初转换超过 8,000 张图像是我需要它的第一步。但是，我也将在我们的软件中使用相同的东西来根据需要在现场自动转换任何图像。所以第三方转换器无法工作，因为我无法将其分发给我们的客户。

Answer 1

我会尝试以下方法。此版本仅适用于 24 位位图：

procedure SwapRedBluePixels(ABitmap: TBitmap);
var
  X: Integer;
  Y: Integer;
  Red: Byte;
  Pixel: PRGBTriple;
begin
  // check for the bit depth, it must be 24-bit if you use PRGBTriple pointer
  // for line scan; if it wouldn't the iterated line pointers would point to 
  // another place in the memory
  if ABitmap.PixelFormat <> pf24bit then
  begin
    ShowMessage('Your bitmap has color depth different from 24-bit');
    Exit;
  end;
  // iterate through the image vertically
  for Y := 0 to (ABitmap.Height - 1) do
  begin
    // access the line of pixels and get the pointer to the first pixel of 
    // that line
    Pixel := ABitmap.ScanLine[Y];
    // iterate through the scanned line pixels horizontally
    for X := 0 to (ABitmap.Width - 1) do
    begin
      // store the pixel's red channel value
      Red := Pixel.rgbtRed;
      // modify the pixel's red channel value
      Pixel.rgbtRed := Pixel.rgbtBlue;
      // modify the pixel's blue channel value
      Pixel.rgbtBlue := Red;
      // increment to get the next pixel pointer of the scanned line
      Inc(Pixel);
    end;
  end;
end;

更新 2：

此版本适用于 24 位和 32 位位图：

procedure SwapRedBluePixels(ABitmap: TBitmap);
var
  X: Integer;
  Y: Integer;
  Red: Byte;
  Size: Integer;
  Pixels: PByteArray;
begin
  // check the color depth and set the size of the pixel arrangement
  case ABitmap.PixelFormat of
    pf24bit: Size := SizeOf(TRGBTriple);
    pf32bit: Size := SizeOf(TRGBQuad);
  else
    // if the image is not 24-bit or 32-bit go away
    begin
      ShowMessage('Your bitmap has unsupported color depth!');
      Exit;
    end;
  end;

  // iterate through the image vertically
  for Y := 0 to (ABitmap.Height - 1) do
  begin
    // access the line of pixels and get the pointer to the first pixel of
    // that line
    Pixels := ABitmap.ScanLine[Y];
    // iterate through the scanned line pixels horizontally
    // for 24-bit images the pixels are stored like
    // B -> G -> R -> B -> G -> R etc.
    // for 32-bit images the pixels are stored like
    // B -> G -> R -> A -> B -> G -> R -> A etc.
    // so we can simply use e.g. byte array and iterate through
    // it, if we have 24-bit image, we have to read each element,
    // if 32-bit we have to skip the alpha (reserved) channel
    for X := 0 to (ABitmap.Width - 1) do
    begin
      // store the pixel's red channel value
      Red := Pixels^[(X * Size) + 2];
      // modify the pixel's red channel value
      Pixels^[(X * Size) + 2] := Pixels^[(X * Size)];
      // modify the pixel's blue channel value
      Pixels^[(X * Size)] := Red;
    end;
  end;
end;