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      StretchBlt(oBitmapStretch.canvas.Handle,  // handle of destination device context
                 0,                             // x -coordinate of upper-left corner of dest. rect.
                 0,                             // y-coordinate of upper-left corner of dest. rect.
                 iNewXSize,                     // width of destination rectangle
                 iNewYSize,                     // height of destination rectangle
                 oBitmapOriginal.canvas.Handle, // handle of source device context
                 0,                             // x-coordinate of upper-left corner of source rectangle
                 0,                             // y-coordinate of upper-left corner of source rectangle
                 oBitmapOriginal.Width,         // width of source rectangle
                 oBitmapOriginal.Height,        // height of source rectangle
                 SRCCOPY                        // raster operation code
                );                    

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{Bildgröße verändern}

procedure TForm1.AnpassenClick(Sender: TObject);
var
  Bitmap1: TBitmap;
  Bitmap2: TBitmap;
begin
  Bitmap1 := TBitmap.Create;
  Bitmap1.LoadFromFile(Edit1.Text);
  Bitmap2 := TBitmap.Create;
  Bitmap2.Width := 350;
  Bitmap2.Height := 350;
  Bitmap2.Canvas.StretchDraw(Rect(0,0,Bitmap2.Width-1,Bitmap2.Height-1),Bitmap1);
  Bitmap2.SaveToFile('./b.bmp');
  Bitmap1.Free;
  Bitmap2.Free;
  Image1.Picture.LoadFromFile('./b.bmp');
end;



procedure TForm1.BildladenClick(Sender: TObject);
begin
OpenPictureDialog1.Execute;
Image1.Picture.LoadFromFile(OpenPictureDialog1.FileName);
Edit1.Text:=(OpenPictureDialog1.FileName);
end;


{bmp nach jpg}


uses JPEG;
Procedure BmpToJpg(const Filename: String; 
Quality: TJPEGQualityRange=100);
var 
Bmp: TBitmap; 
Jpg: TJpegImage;
begin
Bmp:=TBitmap.Create;
Jpg:=TJpegImage.Create;
try  
Bmp.LoadFromFile(Filename);  
Jpg.CompressionQuality:=Quality;
  Jpg.Assign(Bmp);
  Jpg.SaveToFile(ChangeFileExt(Filename, '.jpg' ));
finally 
 Jpg.Free;
  Bmp.Free;
end;
end;


{jpg nach bmp}


uses jpeg;
procedure JpegToBmp(const Filename: String);
var 
jpeg: TJPEGImage; 
bmp: TBitmap;begin jpeg:=TJPEGImage.Create; 
try   
jpeg.LoadFromFile(Filename);   
bmp:=TBitmap.Create;  
 try     
bmp.Assign(jpeg);     
bmp.SaveToFile(ChangeFileExt(Filename, '.bmp'));   
finally     
bmp.free;   
end; 
finally   
jpeg.free; 
end;
end;