Resize PNG in Delphi 11

[programmerdelphi2k 237]

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var
  LPictureSource: TPicture;  // load a PNG
  LPictureTarget: TPicture;  // to resize like a Bitmap
  LPNGresulted  : TPngImage; // to save PNG resulted
  LBtmPointerTmp: TBitmap;
begin
  LBtmPointerTmp := TBitmap.Create(1, 1);
  LPictureSource := TPicture.Create;
  LPictureTarget := TPicture.Create;
  LPNGresulted   := TPngImage.Create;
  try
    LPictureSource.Assign(Image2.Picture);
    // LPictureSource.LoadFromFile('..\..\IronMan.png');
    LPictureSource.Graphic.Transparent := True;
    //
    Memo1.Text := 'IronMan.png = ' + LPictureSource.Width.ToString + 'x' + LPictureSource.Height.ToString;
    //
    LPictureTarget.Bitmap.Assign(LBtmPointerTmp); // Create(1, 1); // just for create intervalues values to canvas, etc...
    LPictureTarget.Graphic.Transparent := True;
    //
    // new size
    LPictureTarget.Bitmap.SetSize( Trunc(LPictureSource.Width * 0.4), Trunc(LPictureSource.Height * 0.4) );
    //
    // draw on new canvas resized
    LPictureTarget.Bitmap.Canvas.StretchDraw(LPictureTarget.Bitmap.Canvas.ClipRect, LPictureSource.Graphic);
    //
    Memo1.Lines.Add(LPictureTarget.Width.ToString + 'x' + LPictureTarget.Height.ToString);
    //
    LPNGresulted.Assign(LPictureTarget.Bitmap);
    //
    Memo1.Lines.Add('PNG = ' + LPNGresulted.Width.ToString + 'x' + LPNGresulted.Height.ToString);
    //
    LPNGresulted.SaveToFile('resulted.png'); // just for test load file...
    //
    Image1.Picture.LoadFromFile('resulted.png');
    Image1.Proportional := True;
  finally
    LPNGresulted.Free;
    LPictureTarget.Free;
    LPictureSource.Free;
    LBtmPointerTmp.Free;
  end;
end;

initialization

ReportMemoryLeaksOnShutdown := True;

finalization

end.

 

Edited February 9, 2023 by programmerdelphi2k

[programmerdelphi2k 237]

ok

[dmitrok2006 2]

Strange... of course... But when I add the saved picture to photoshop, the picture with a white background...

[Anders Melander 1782]

Just so you know, while all the code in this thread might be fine for "I'm a hobbyist and I don't know what the hell I'm doing"-level programming, it's nowhere near the best or correct way to solve your problem.

 

With that said, the reason you're losing transparency is that you are operating on the rendered visual representation of the image. Therefore the transparency has been replaced with a background color.

In order to resize a PNG without losing transparency you will need to use a method that supports alpha transparency. This means:

1. Convert the PNG to a 32-bit RGBA bitmap.
2. Resample (resize) this bitmap to the desired size.
3. Convert the bitmap to PNG.

There are various libraries that can do these steps for you. For example Graphics32 and probably also Image32. I'm guessing Image32 will probably be the easiest for you to understand.

[programmerdelphi2k 237]

sorry Melander, as you know my knowledge is not near your, but it's the life!!! Luck for us "have someone like you" for fix our error!  

go ahead...

 

in my test, the "Ironman - result.png" have background transparent

 

     

Edited February 10, 2023 by programmerdelphi2k

[programmerdelphi2k 237]

[dmitrok2006 2]

In any case, thanks for the help. )))

[programmerdelphi2k 237]

not for that