I need help in replacing white background of a png image to transparent using im4java API not by using the command line

Question

I tried to replace the white background of an image with a transparent one using the below lines,

IMOperation op = new IMOperation();
op.fuzz(0.20,true);
//op.transparent("white");
op.addImage("C:\\write\\test.png");
op.addImage("C:\\test\\result.png");
ConvertCmd cmd =new ConvertCmd();
cmd.run(op);

but I'm getting an error - invalid parameter 0.2%

Can someone help here?