Phone中图片的拉伸/圆角处理(Image round corner, aspect fit)

图片圆角 image round corner:
m_mainImgView.layer.cornerRadius = 6;
m_mainImgView.layer.masksToBounds = YES;

自动适应,保持图片宽高比 aspect fit:
m_mainImgView.contentMode = UIViewContentModeScaleAspectFit;

见下图:
Ori:

round corner:

Aspect Fit: