How to desaturate image?

[User137]

Function Gray(vColor:TByte4):TByte4;
Var
  vAverage:TFlt;
begin
  vAverage:=vColor.R*0.3+vColor.G*0.59+vColor.B*0.11;
  result.R:=Round(vAverage);
  result.G:=Round(vAverage);
  result.B:=Round(vAverage);
  result.A:=vColor.A;
end;

Round() would be bottlenecking that

Function Gray(vColor:TByte4):TByte4;
Var
  vAverage: byte;
begin
  vAverage:=round(vColor.R*0.3+vColor.G*0.59+vColor.B*0.11);
  result.R:=vAverage;
  result.G:=vAverage;
  result.B:=vAverage;
  result.A:=vColor.A;
end;

The function should work, if you are getting black you are not using it with right parameters and result value. It's not directly compatible with TColor if that is the type.