【iOS】根据尺寸和比例缩放图片

根据尺寸

//根据指定尺寸缩放图片
-(UIImage *)imageCompressWithSize:(CGSize)size
{
**//    UIGraphicsBeginImageContext(size);   ///<用这个失真**
    UIGraphicsBeginImageContextWithOptions(size, NO, 0.0);    ///<用这个不失真
    [self drawInRect:CGRectMake(0, 0, size.width, size.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

之前用模拟器跑是没有问题，但是在真机运行时用这个方法缩小的图片过于模糊，最后发现使用UIGraphicsBeginImageContext(size);方法会造成失真，换成UIGraphicsBeginImageContextWithOptions(size, NO, 0.0); 就可以

根据比例缩放

//根据指定比例缩放图片
-(UIImage *)imageCompressWithScale:(CGFloat)scale
{
    
    CGSize size = self.size;
    CGFloat width = size.width;
    CGFloat height = size.height;
    CGFloat scaleWidth = width*scale;
    CGFloat scaleHeight = height*scale;
    UIGraphicsBeginImageContextWithOptions(CGSizeMake(scaleWidth, scaleHeight), NO, 0.0);    ///<用这个不失真
    [self drawInRect:CGRectMake(0, 0, scaleWidth, scaleHeight)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}