需求背景

测试找到我说：“你这个图也太丑了，严重影响了整体的协调性，能不能改的小点” 我说：“这简单啊，小case”一分钟后，测试MM又来了：“图片怎么都失真了？” “我看看” 真的失真了，而且很明显的锯齿状...奇了个怪了
我是如是做的

- (UIImage *)imageScaled:(float)sizeScale
{
    CGSize size = CGSizeMake(self.size.width * sizeScale, self.size.height * sizeScale);

    UIGraphicsBeginImageContext(size);

    [self drawInRect:CGRectMake(0, 0, self.size.width * sizeScale, self.size.height * sizeScale)];
    
    UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
    
    UIGraphicsEndImageContext();
    
    return scaledImage;
    
}

想了想，点进UIGraphicsBeginImageContext里看了看

// UIImage context

// The following methods will only return a 8-bit per channel context in the DeviceRGB color space.
// Any new bitmap drawing code is encouraged to use UIGraphicsImageRenderer in leiu of this API.
UIKIT_EXTERN void     UIGraphicsBeginImageContext(CGSize size);
UIKIT_EXTERN void     UIGraphicsBeginImageContextWithOptions(CGSize size, BOOL opaque, CGFloat scale) NS_AVAILABLE_IOS(4_0);
UIKIT_EXTERN UIImage* __nullable UIGraphicsGetImageFromCurrentImageContext(void);
UIKIT_EXTERN void     UIGraphicsEndImageContext(void); 

目光聚焦在了UIKIT_EXTERN void UIGraphicsBeginImageContextWithOptions(CGSize size, BOOL opaque, CGFloat scale) NS_AVAILABLE_IOS(4_0); 这个方法上

试了一会，最后成型

#pragma mark - 缩放图片不失真
- (UIImage *)imageScaled:(float)sizeScale
{
    CGSize size = CGSizeMake(self.size.width * sizeScale, self.size.height * sizeScale);
    
    if([[UIScreen mainScreen] scale] == 3.0){
        UIGraphicsBeginImageContextWithOptions(size, NO, 3.0);
    }else  if([[UIScreen mainScreen] scale] == 2.0){
        UIGraphicsBeginImageContextWithOptions(size, NO, 2.0);
    }else{
        UIGraphicsBeginImageContext(size);
    }
    [self drawInRect:CGRectMake(0, 0, self.size.width * sizeScale, self.size.height * sizeScale)];
    
    UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
    
    UIGraphicsEndImageContext();
    
    return scaledImage;
    
}

Prefect 测试mm也很满足（😌）

再回看这个方法 UIKIT_EXTERN void UIGraphicsBeginImageContextWithOptions(CGSize size, BOOL opaque, CGFloat scale) NS_AVAILABLE_IOS(4_0);

• 第一个参数size 就是你想要的尺寸
• 第二个参数opaque（直译‘不透明’）如果YES背景是黑的，NO背景是透明的
• 第三个参数 scale 是屏幕的比例，其实就是2x ，3x屏

最后插句嘴 ，我这个方法是写在分类里的

如果你想直接来，可以这样

- (UIImage *)scaleImage:(UIImage *)orginImage withScale:(float)sizeScale
{
    CGSize size = CGSizeMake(orginImage.size.width * sizeScale, orginImage.size.height * sizeScale);
    
    if([[UIScreen mainScreen] scale] == 3.0){ 
               UIGraphicsBeginImageContextWithOptions(size, NO, 3.0);
    }else if([[UIScreen mainScreen] scale] == 2.0){  
              UIGraphicsBeginImageContextWithOptions(size, NO, 2.0);
    }else{
        UIGraphicsBeginImageContext(size);
    }
    [orginImage drawInRect:CGRectMake(0, 0, orginImage.size.width * sizeScale, orginImage.size.height * sizeScale)];
    
    UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
    
    UIGraphicsEndImageContext();
    
    return scaledImage;
    
}