How to save a png file with transparency?

Question

I am using Barcode Studio 2011 to paint a QR Code into a Graphics32 - TImage32 Component and I want to save it in png format but with the white colour as transparent this I

Answer 1

You haven't specified the Delphi version, but if your delphi version has "PngImage"(I believe it comes with D2009+) the code bellow works perfectly(loaded in Gimp and Windows Photo Viewer, it draws a frame and some text with transparent background, feel free to play with it:

uses
  PngImage;

procedure TForm1.OnBtnClick(Sender: TObject);
var
  bmp: TBitmap;
  png: TPngImage;
begin
  bmp := TBitmap.Create;
  bmp.Width := 200;
  bmp.Height := 200;

  bmp.Canvas.Brush.Color := clBlack;
  bmp.Canvas.Rectangle( 20, 20, 160, 160 );

  bmp.Canvas.Brush.Style := bsClear;
  bmp.Canvas.Rectangle(1, 1, 199, 199);

  bmp.Canvas.Brush.Color := clWhite;
  bmp.Canvas.Pen.Color := clRed;
  bmp.Canvas.TextOut( 35, 20, 'Hello transparent world');

  bmp.TransparentColor := clWhite;
  bmp.Transparent := True;

  png := TPngImage.Create;
  png.Assign( bmp );
  png.SaveToFile( 'C:\test.png' );

  bmp.Free;
  png.Free;
end;