请问jpeg-》bmp-》jpeg的转化问题

Question

我的源文件为256级灰度，经历了上述转化后出来的jpeg却是24b的，怎么我限定了最后的jpeg为jp8bit但是图象不正常（无信息），应该是格式不对，但我限定bmp为bp8bit，可是最后得到的jpeg还是24b的。请问我要怎么办啊

Answer 1

use jpeg; 
var
  MyJpeg: TJpegImage;
  Image1: TImage;
begin
  Image1:= TImage.Create(self);
  MyJpeg:= TJpegImage.Create;
  Image1.Picture.Bitmap.LoadFromFile('c:.BMP'); // Load the Bitmap from a file
  MyJpeg.Assign(Image1.Picture.Bitmap); // Assign the BitMap to MyJpeg object
  MyJpeg.CompressionQuality:=StrToInt('75');
  MyJpeg.Compress;
  MyJpeg.SaveToFile('c:.JPG'); // Save the JPEG to Disk
end;var
  MyJpeg: TJpegImage;
  bmp: Tbitmap;
begin
  bmp:=tbitmap.Create;
  MyJpeg:= TJpegImage.Create;
  myjpeg.LoadFromFile('c:.jpg');
  bmp.Assign(myjpeg);
  bmp.SaveToFile('c:.bmp'); // Save the JPEG to Disk
end;

Answer 2

感谢dext(德克斯特)前辈，这个方法不错的

Answer 3

use jpeg;**********************（  jpeg to  bmp  ）*****************************
procedure Tfrm_Probation.bsSkinButton5Click(Sender: TObject);
var
  ImageBMP:Tbitmap;
  ImageJPEG:Tjpegimage;
begin
try
  if OpenPictureDialog1.Execute then
  begin
    if uppercase(ExtractFileExt(OpenPictureDialog1.FileName))='.BMP' then
    begin
      ImageBMP:=Tbitmap.Create;
      ImageJPEG:=TjpegImage.Create;
      ImageJPEG.LoadFromFile(bsSkinOpenPictureDialog1.FileName);
      ImageJPEG.Assign(ImageBMP);
      ImageJPEG.SaveToFile(ExtractFilePath(application.ExeName)+'TempBMP.JPEG');
      Image1.Picture.LoadFromFile(ExtractFilePath(application.ExeName)+'TempBMP.JPEG');
    end
    else
     Image1.Picture.LoadFromFile(OpenPictureDialog1.FileName);
  end;
  except
 Message1.MessageDlg('您选择的图片格式有误，请从新选择！', mtInformation, [mbOK], 0);
  exit;
  end;
end;**********************（  bmp to  jpeg ）*****************************procedure Tfrm_Probation.bsSkinButton5Click(Sender: TObject);
var
  ImageBMP:Tbitmap;
  ImageJPEG:Tjpegimage;
begin
try
  if OpenPictureDialog1.Execute then
  begin
    if uppercase(ExtractFileExt(OpenPictureDialog1.FileName))='.JPG' then
    begin
      ImageBMP:=Tbitmap.Create;
      ImageJPEG:=TjpegImage.Create;
      ImageJPEG.LoadFromFile(bsSkinOpenPictureDialog1.FileName);
      ImageBMP.Assign(ImageJPEG);
      ImageBMP.SaveToFile(ExtractFilePath(application.ExeName)+'TempBMP.BMP');
      Image1.Picture.LoadFromFile(ExtractFilePath(application.ExeName)+'TempBMP.BMP');
    end
    else
     Image1.Picture.LoadFromFile(OpenPictureDialog1.FileName);
  end;
  except
 Message1.MessageDlg('您选择的图片格式有误，请从新选择！', mtInformation, [mbOK], 0);
  exit;
  end;
end;

Answer 4

给你贴一段代码，绝对能用，
Jpeg-file to bmp-file
/////////////////////////////////////////////////
Button1Click procedure creates variable of TJPEGImage type and loads a picture stored in a file.
Button2Click procedure creates variable of TBitmap type and sets jpeg object to this variable. suses JPEG;
...
var
 JPEGImage: TJPEGImage;
...
procedure TForm1.Button1Click(Sender: TObject);
begin
  JPEGImage:=TJPEGImage.Create;
  if OpenDialog1.Execute then
  begin
    JPEGImage.LoadFromFile(OpenDialog1.FileName);
    Image1.Canvas.Draw(0,0,JPEGImage);
  end;
end;procedure TForm1.Button2Click(Sender: TObject);
var
  Bitmap: TBitmap;
begin
  try
    Bitmap:=TBitmap.Create;
    with Bitmap do
    begin
      PixelFormat:=pf24bit;
      Height:=JPEGImage.Height;
      Width:=JPEGImage.Width;
      Canvas.Draw(0,0, JPEGImage);
    end;
    if SaveDialog1.Execute then
      Bitmap.SaveToFile(SaveDialog1.FileName);
    Label1.Caption:='Convertation finised';
  finally
    Bitmap.Free;
    JPEGImage.Free;
  end;
end;

Answer 5

接着：BMP to JPG
Button1Click procedure creates variable of TBitmap type and loads a picture stored in a file.
Button2Click procedure creates variable of TJPEGImage type and assignes bitmap object to this variable. uses JPEG;
...
var
  Bitmap: TBitmap;
...
procedure TForm1.Button1Click(Sender: TObject);
begin
  if OpenDialog1.Execute then
  begin
    Bitmap:=TBitmap.Create;
    Bitmap.LoadFromFile(OpenDialog1.FileName);
    Image1.Picture.LoadFromFile(OpenDialog1.FileName);
  end;
end;procedure TForm1.Button2Click(Sender: TObject);
var
  JPEGImage: TJPEGImage;
begin
  try
    JPEGImage:=TJPEGImage.Create;
    JPEGImage.CompressionQuality:=80;
    JPEGImage.Assign(Bitmap);
    if SaveDialog1.Execute then
      JPEGImage.SaveToFile(SaveDialog1.FileName);
    Label1.Caption:='Convertation finished';
  finally
    Bitmap.Free;
    JPEGImage.Free;
  end;
end;