code: function readImageInfo(fileName, callback) {
      fileName = path.join(spriteConfig.workspace, fileName);
      fs.createReadStream(fileName).pipe(new PNG())
          .on('parsed', function() {
  
              var imageInfo = {
                  image: this,
                  width: this.width,
                  height: this.height
              };
  
              getImageSize(this, function(size) {
  
                  imageInfo.size = size;
                  callback(imageInfo);
              });
          })
          .on('error', function(e) {
              info('>>Skip: ' + e.message + ' of "' + fileName + '"');
              callback(null);
          });
  }
docs: 读取单个图片的内容和信息
  @param {String} fileName
  @param {Function} callback callback(ImageInfo)
  { // ImageInfo
  image: null, // 图片数据
  width: 0,
  height: 0,
  size: 0 // 图片数据的大小
  }