OC 任意区域截屏

    UIGraphicsBeginImageContext(self.view.bounds.size); 

    [self.view.layer renderInContext:UIGraphicsGetCurrentContext()];

    UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

上面的方法截出来的图很模糊，建议使用下面的方法

//opaque 透明度，不透明设为YES；

//scale  缩放因子，设0时系统自动设置缩放比例图片清晰；设1.0时模糊

UIGraphicsBeginImageContextWithOptions(_posterView.size,YES,0.0);

[_posterView.layerrenderInContext:UIGraphicsGetCurrentContext()];

UIImage*image =UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

UIImageWriteToSavedPhotosAlbum(image, self,@selector(image:didFinishSavingWithError:contextInfo:), nil);