update image DPI in node js

I am able to resize ,rotate,crop etc with current node modules like sharp,lwip but not able to change image DPI via these modules. it creates new image with same DPI.Here is my code:

const image = sharp('subject1.png');
image.metadata()
  .then(function (metadata,info) {
    var write = fs.createWriteStream( "newPath.png" );
    var transform = sharp().resize( 800, 900 ).quality( 80 );

    var obj2 = JSON.parse(JSON.stringify(metadata));
    // metadata.density = 220;
    obj2.density=72;
    // var stream = fs.createWriteStream( "subject12.png" ).setMetadata(obj2);
     image.withMetadata(obj2).toFile("sub11.png",function(err){ console.log("Testing Data",err)})


  });

via Siddhartha