Convert JPEG to BMP and vice versa - there is nothing essentially a complex.  Jpeg is used to compress the image, but here there is the disadvantage that if you use very high compression ratio for the jpeg-files, the image is just simply could break (begin to fall) into blocks of pixels. In bmp-images for display provides a color assigned from 1 to 48 bits. Probably the most commonly used - is 24 bits at 48 bits - This format is rarely used with high color accuracy and, accordingly, it will be much larger in size than the same with 24 bits of color, and so the data transfer (conversion) we will reduce the image size and different.
Let us then install all the necessary components:

    * TGroupBox - 2 pcs
    * TEdit - 2 pcs
    * TLabel - 2 pcs
    * TButton - 6 pieces
    * TOpendialog
    * TSaveDialog
I n one block, we will convert jpeg to bmp, and in another unit vice-versa. In addition, we need to connect the module uses jpeg, so we can work with jpeg-images in Delphi. After that, we will understand how to convert BMP to JPEG. Now write the code to open a bmp-file.
Source code
procedure TForm1.Button1Click (Sender: TObject);
begin
   if OpenDialog1.Execute then
    Edit1.Text: = OpenDialog1.FileName
   else
    exit;
end;
And now the code that will specify the name, is retained (output) jpeg-file.
Source code
procedure TForm1.Button2Click (Sender: TObject);
begin
   if SaveDialog1.Execute then
    begin
     Edit2.Text: = SaveDialog1.FileName + '. Jpg';
    end
   else
    exit;
end;
Well, and now has begun to convert most of our images on the buttons OnClick write the code
Source code
procedure TForm1.Button3Click (Sender: TObject);
var
 jpg: TJPEGImage;
 bmp: TBitmap;
begin
   try
    jpg: = TJPEGImage.Create;    bmp: = TBitmap.Create;    bmp.LoadFromFile (Edit1.Text);    jpg.Assign (bmp);    jpg.SaveToFile (Edit2.Text);    jpg.Free;    FreeAndNil (bmp);
   except
    on e: Exception do
     begin
      jpg.Free;
      bmp.Free;
     end;
   end;
end;
Do not forget to plug in uses jpeg.  We create an instance of TGraphic - jpeg and bmp. Then we load a bmp image that we need to convert, and then use the Assign save it in jpeg, after which the previously created the file, save our jpeg-file on disk. Now you can test very easily, if no bmp-images, then it is very easy to create - open mspaint and draw a couple lines and save as bmp-image, then open it and click on the button "Convert", compare their size - differ greatly.

We now proceed to the opposite effect - Convert JPEG to BMP. Code to open the jpeg-file the same
Source code

procedure TForm1..Button4Click (Sender: TObject);
begin,
   if OpenDialog1.Execute then
    Edit3.Text: = OpenDialog1.FileName
   else
    exit;
end;

To preserve nearly the same
Source code

procedure TForm1.Button5Click (Sender: TObject);
begin
   if SaveDialog1.Execute then
    Edit4.Text: = SaveDialog1.FileName
   else
    exit;
end;

And now the code that converts our image
Source code

procedure TForm1.Button6Click (Sender: TObject);
var
 jpg: TJPEGImage; bmp: TBitmap;begin;   try    jpg: = TJPEGImage.Create;    bmp: = TBitmap.Create;     jpg.CompressionQuality: = 100;    jpg.Compress;    jpg.LoadFromFile (Edit3.Text);    bmp.Assign (jpg);    bmp.SaveToFile (ChangeFileExt (Edit4.Text, '. bmp'));    FreeAndNil (jpg);    FreeAndNil (bmp);   except    on e: Exception do;      begin;      FreeAndNil (jpg);      FreeAndNil (bmp);     end;   end;end;