TImage32.AdjustLuminance

procedure AdjustLuminance(percent: Integer);

percent range: -100 .. 100

uses Img32, Img32.Fmt.PNG;
...
img := TImage32.Create;
img.LoadFromFile('beetle.png');
img.AdjustLuminance(-30);
img.SaveToFile('beetle_hue.png');
img.Free;

Before:

After: