var gm = require('gm').subClass({imageMagick: true})var tanpwd = process.cwd()var code = {    getCode:function(){         gm(tanpwd+'\\config\\bg.jpg')// 原圖路徑                  .write(tanpwd+'\\upload\\b.png', function (e) {// 輸出的圖片路徑             if(e) {                console.log(e.message)             }else {                console.log('done')             }         })     } }module.exports = code一直說我參數錯誤Command failed: Invalid Parameter - C:xxxxxxxxxxxxuploadb.png所以這東西到底怎么用imageMagick