제가 사용했던 함수입니다...

ImageRotate90() 이 함수를 호출하면 돌아갈겁니다.

즐프하세요...


{ this functions returns the number of bytes needed to represent 1 pixel
        in the current PixelFormat of the bitmap. }
function GetPixelSize(aBitmap: TBitmap): Integer;
var
  nBitCount, nMultiplier: Integer;
begin

  case aBitmap.PixelFormat of
    pfDevice : begin
                 nBitCount   := GetDeviceCaps(aBitmap.Canvas.Handle, BITSPIXEL);
                 nMultiplier := nBitCount div BitsPerByte;
                 if (nBitCount mod BitsPerByte)>0 then
                 begin
                   Inc(nMultiplier);
                 end;
               end;
    pf1bit   : nMultiplier := 1;
    pf4bit   : nMultiplier := 1;
    pf8bit   : nMultiplier := 1;
    pf15bit  : nMultiplier := 2;
    pf16bit  : nMultiplier := 2;
    pf24bit  : nMultiplier := 3;
    pf32bit  : nMultiplier := 4;
  else
    //raise EInvalidPixelFormat.Create('Bitmap pixelformat is unknown.');
    nMultiplier := 2;
  end;
  Result := nMultiplier;
end;

{ this procedure rotates the image counterclockwise by 90 degrees.
        i could have made this routine rotate clockwise but doing it in
        counter-clockwise is easier and thus less prone to bugs.

        what we do here is grab the first scanline and distribute each pixel
        along one column of the new image (or in this case new scanlines buffer)
        we do this until we run out of scanlines then we are done.}

procedure ImageRotate90(aBitmap: TBitmap);
var
  nIdx, nOfs,
  x, y, i,
  nMultiplier: integer;
  nMemWidth, nMemHeight, nMemSize,
  nScanLineSize: LongInt;

  aScnLnBuffer: PChar;
  aScanLine: PByteArray;
begin
  nMultiplier := GetPixelSize(ABitmap);
  nMemWidth   := aBitmap.Height;
  nMemHeight  := aBitmap.Width;
  nMemSize    := nMemWidth * nMemHeight * nMultiplier;

  GetMem(aScnLnBuffer, nMemSize);
  try
    nScanLineSize := aBitmap.Width * nMultiplier;
    GetMem(aScanLine, nScanLineSize);
    try
      for y := 0 to aBitmap.Height-1 do
      begin
        Move(aBitmap.ScanLine[y]^, aScanLine^, nScanLineSize);
        for x := 0 to aBitmap.Width-1 do
        begin
          nIdx := ((aBitmap.Width-1) - x) * nMultiplier;
          // y component of the dst x component of the dst
          nOfs := (x * nMemWidth * nMultiplier) + (y * nMultiplier);
          for i := 0 to nMultiplier-1 do
            Byte(aScnLnBuffer[nOfs + i]) := aScanLine[nIdx+i];
        end;
      end;

      aBitmap.Height := nMemHeight;
      aBitmap.Width  := nMemWidth;

      for y := 0 to nMemHeight-1 do
      begin
        nOfs := y * nMemWidth * nMultiplier;
        Move((@(aScnLnBuffer[nOfs]))^, aBitmap.ScanLine[y]^, nMemWidth * nMultiplier);
      end;

    finally
      FreeMem(aScanLine, nScanLineSize);
    end;
  finally
    FreeMem(aScnLnBuffer, nMemSize);
  end;
end;