title: UIImage resize performance and quality issue
body: <p>I'm working with UIImage and like everyone else have to deal with retina and non-retina display adaptability. As for as I know, retina display requires double pixels.</p>
  
  <p>I'm wondering if I could simply use a large image with the same width/height ratio, just resize it smaller to adapt all device?</p>
  
  <p>For example, I made a original image with size of 200*200 pixel. Now I want to use it in application as 20*20 pixel, and 80*80 pixel (two situations). Then I have to make four copies like img2020.png, img2020@2x.png, img8080.png and img8080@2x.png</p>
  
  <p>So if I want to use it in three situations with difference size, I have  to store 6 copies. Can I just use UIImage's resize function to do this? I've tried a bit but cannot figure out it's quality and performance.</p>
  
  <p>Any ideas? Thanks a lot :)</p>