Delphi – Convert BMP to PNG failed

if Clipboard.HasFormat (CF_PICTURE) then
begin
 bitmap := TBitmap.Create;
 png := TPNGImage.Create;
 try
 bitmap.Assign(Clipboard);
 bitmap.SaveToFile(ExtractFilePath(application.ExeName) +'ilename.bmp');
 png.Draw(bitmap.Canvas, Rect(0, 0, bitmap.Width, bitmap.Height));
 png.SaveToFile(extractfilepath(application.ExeName) +'ilename.png');
 finally
 bitmap.free;
 png.free;
 end;
end;

You have not set the size (height and width) of the PNG image object. You need to do this before drawing Do.

However, it is easier to do a simple task:

png.Assign(Bitmap);

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I have the following simple code to convert a clipboard image to bmp and then to png:

if Clipboard.HasFormat(CF_PICTURE ) then
begin
 bitmap := TBitmap.Create;
 png := TPNGImage.Create;
 try
 bitmap.Assign(Clipboard);
 bitmap .SaveToFile(ExtractFilePath(application.ExeName) +'ilename.bmp');
 png.Draw(bitmap.Canvas, Rect(0, 0, bitmap.Width, bitmap.Height));
 png.SaveToFile(extractfilepath(application.ExeName) +'ilename.png');
 finally
 bitmap.free;
 png.free;
 end;
 end;

Although the conversion to bmp works, I can even open it in mspaint and view its content, the conversion to png fails, and I have a blank png image. What am I doing wrong?

You have not set the size (height and width) of the PNG image object. You need to do this before drawing.

However, it is easier to do a simple task:

png.Assign(Bitmap);