TImage32.ScaleAlpha

procedure ScaleAlpha(scale: double);


Scales the alpha byte of every pixel by the specified amount.

uses Image32, Image32_PNG, Image32_vector, Image32_Extra;
...
var
img: TImage32;
path: TArrayOfPointD;
begin
img := TImage32.Create;
img.LOadFromFile('glowing_star.png');

img.ScaleAlpha(4);    
img.SaveToFile('extra_glowing_star.png');
img.Free;
end;
      
Before:
After: