docs: function _compress(command, outputFile) {
      return qexec(command)
          .then(function () {
              return outputFile.loadSize();
          })
          .fail(function (err) {
              // Before using of 'advpng' a raw file has to be copied
              // This algorithm can not compress a file and write a result to another file
              return qfs.exists(outputFile.name)
                  .then(function (exists) {
                      if (exists) {
                          outputFile.remove();
                      }
  
                      throw err;
                  });
          });
  }