image改变size时不清晰的问题

不清晰写法

- (UIImage *)reSizeImage:(UIImage *)image toSize:(CGSize)reSize

{

     UIGraphicsBeginImageContext(reSize);

     [image drawInRect:CGRectMake(0, 0, reSize.width, reSize.height)];

     UIImage *reSizeImage = UIGraphicsGetImageFromCurrentImageContext();

     UIGraphicsEndImageContext();

     return reSizeImage;

}

修改过后

-(UIImage *)reSizeImage:(UIImage *)image toSize:(CGSize)reSize
{

    //instead of UIGraphicsBeginImageContext(reSize);

    UIGraphicsBeginImageContextWithOptions(reSize, YES, 0); 

    [image drawInRect:CGRectMake(0, 0, reSize.width, reSize.height)];

    UIImage *reSizeImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return reSizeImage;

}

补充说明

void UIGraphicsBeginImageContextWithOptions(CGSize size, BOOL opaque, CGFloat scale);
size——同UIGraphicsBeginImageContext
opaque——透明开关，如果图形完全不用透明，设置为YES以优化位图的存储。
scale—–缩放因子：设为0后，系统就会自动设置正确的比例了