下面这个方法的确能压缩图片，但是图片会变形

//对图片尺寸进行压缩--
- (UIImage*)imageWithImage:(UIImage*)image scaledToSize:(CGSize)newSize {
    // Create a graphics image context
    UIGraphicsBeginImageContext(newSize);
    
    // Tell the old image to draw in this new context, with the desired
    // new size
    [image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
    
    // Get the new image from the context
    UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
    
    // End the context
    UIGraphicsEndImageContext();
    
    // Return the new image.
    return newImage;
}

因为是按照指定尺寸压缩，导致图片压缩之后模糊，失真

按照屏幕的尺寸压缩，则会保证不失真

- (UIImage*)imageCompressWithSimple:(UIImage*)image{
    CGSize size = image.size;
    CGFloat scale = 1.0;
    //TODO:KScreenWidth屏幕宽
    
    CGFloat KScreenWidth = [UIScreen mainScreen].bounds.size.width;
    CGFloat KScreenHeight = [UIScreen mainScreen].bounds.size.height;
    
    if (size.width > KScreenWidth || size.height > KScreenHeight) {
        if (size.width > size.height) {
            scale = KScreenWidth / size.width;
        }else {
            scale = KScreenHeight / size.height;
        }
    }
    CGFloat width = size.width;
    CGFloat height = size.height;
    CGFloat scaledWidth = width * scale;
    CGFloat scaledHeight = height * scale;
    CGSize secSize =CGSizeMake(scaledWidth, scaledHeight);
    //TODO:设置新图片的宽高
    UIGraphicsBeginImageContext(secSize); // this will crop
    [image drawInRect:CGRectMake(0,0,scaledWidth,scaledHeight)];
    UIImage* newImage= UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}