Panorama is blurred by three.js

Question

I made a panorama using three.js in the mobile but its blurred. I also tried to use krpano and the effect is ok.

here is an image with three.js effect：three.js here is one in krpano

I know to use renderer.setPixelRatio(window.devicePixelRatio), but it is still blurred

I expect the effect in the three.js like in the krpano