How to use imagemagick add more white space around the image

Question

How to use https://github.com/rsms/node-imagemagick add more white space around the image ? example original image is width:300, height:100, I want to generate new image is width: 600, height: 200 the original image is in center stay original size, add white space around to become new image..

I tried below code but this make the original image become 600*200 ... how to solve it?

function cropGravity(srcFilePath, dstFilePath, resizeWidth, resizeHeight, quality, gravity) {
  return new Promise(function (resolve, reject){
    im.crop({
      srcPath: srcFilePath,
      dstPath: dstFilePath,
      width: resizeWidth,
      height: resizeHeight,
      quality: quality,
      gravity: gravity
    }, function(error, stdout, stderr){
      if (error != null) {
        console.log(error)
        reject(error);
      } else {
        resolve(dstFilePath);
      }
    });
  });
};

...
var resizeWidth = 600;
var resizeHeight = 200;
var quality = 1;
var gravity = 'Center';
cropGravity(srcFilePath, dstFilePath, resizeWidth, resizeHeight, quality, gravity)

Answer 1

I really don't speak node, but it will likely be similar to this:

im.convert(['input.jpg', '-gravity', 'center', '-background','white', '-extent', '600x200','result.jpg'], 
function(err, stdout){
  if (err) throw err;
  console.log('stdout:', stdout);
});