gm/convert binaries can't be found

var gm = require("gm").subClass({ imageMagick: true });

控制台log显示：Could not execute GraphicsMagick/ImageMagick: convert "public/assets/poster.png" "tmp/test.png" this most likely means the gm/convert binaries can't be found

如何在计算引擎里安装ImageMagick库呢？或者有别的图片处理替代库也可以