图片压缩封装的代码，不怎么失真

typedef NS_ENUM(NSInteger,CompressType){
    session = 800,
    timeline = 1280
};

@interface XYTool : NSObject

//生成缩略图
+(NSData *)base64ImageThumbnaiWith:(UIImage *)image{
    
    UIImage * newImage = nil;
    //CGSizeMake(100, 100)
    XYTool * reduce = [XYTool new];
    CGSize size = [reduce imageSize:image.size andType:timeline];
    
    if (image == nil) {
        
        newImage = nil;
        
    }else{
        
        UIGraphicsBeginImageContext(size);
        
        [image drawInRect:CGRectMake(0, 0, size.width, size.height)];
        
        newImage = UIGraphicsGetImageFromCurrentImageContext();
        
        UIGraphicsEndImageContext();
        
    }
    
    UIImage *baseImage = newImage;
    
    NSData * data = UIImageJPEGRepresentation(baseImage, 0.5);
    
    return data;
}

/// imageSize大小
-(CGSize)imageSize:(CGSize)size andType:(CompressType)type{
    //计算大小
    CGFloat boundary = 1280;
    CGFloat width = size.width;
    CGFloat height = size.height;
    
    if (width <= boundary || height <= boundary) {
        return CGSizeMake(width, height);
    }
    int proportion = MAX(width, height)/MIN(width, height);
    if (proportion <= 2) {
        int x = MAX(width, height)/boundary;
        if (width > height) {
            width = boundary;
            height = height/x;
        }else{
            width = width/x;
            height = boundary;
        }
    }else{
        if (MIN(width, height)>=boundary) {
            boundary = type == session?800:1280;
            int x = MIN(width, height)/boundary;
            if (width<height) {
                width = boundary;
                height = height/x;
            }else{
                width = width/x;
                height = boundary;
            }
        }
    }
    return CGSizeMake(width, height);
}

/*!
 *  @brief 使图片压缩后刚好小于指定大小
 *
 *  @param image 当前要压缩的图 maxLength 压缩后的大小
 *
 *  @return 图片对象
 */
//图片质量压缩到某一范围内，如果后面用到多，可以抽成分类或者工具类,这里压缩递减比二分的运行时间长，二分可以限制下限。
- (UIImage *)compressImageSize:(UIImage *)image toByte:(NSUInteger)maxLength{
    //首先判断原图大小是否在要求内，如果满足要求则不进行压缩，over
    CGFloat compression = 1;
    NSData *data = UIImageJPEGRepresentation(image, compression);
    if (data.length < maxLength) return image;
    //原图大小超过范围，先进行“压处理”，这里 压缩比 采用二分法进行处理，6次二分后的最小压缩比是0.015625，已经够小了
    CGFloat max = 1;
    CGFloat min = 0;
    for (int i = 0; i < 6; ++i) {
        compression = (max + min) / 2;
        data = UIImageJPEGRepresentation(image, compression);
        if (data.length < maxLength * 0.9) {
            min = compression;
        } else if (data.length > maxLength) {
            max = compression;
        } else {
            break;
        }
    }
    //判断“压处理”的结果是否符合要求，符合要求就over
    UIImage *resultImage = [UIImage imageWithData:data];
    if (data.length < maxLength) return resultImage;
    
    //缩处理，直接用大小的比例作为缩处理的比例进行处理，因为有取整处理，所以一般是需要两次处理
    NSUInteger lastDataLength = 0;
    while (data.length > maxLength && data.length != lastDataLength) {
        lastDataLength = data.length;
        //获取处理后的尺寸
        CGFloat ratio = (CGFloat)maxLength / data.length;
        CGSize size = CGSizeMake((NSUInteger)(resultImage.size.width * sqrtf(ratio)),
                                 (NSUInteger)(resultImage.size.height * sqrtf(ratio)));
        //通过图片上下文进行处理图片
        UIGraphicsBeginImageContext(size);
        [resultImage drawInRect:CGRectMake(0, 0, size.width, size.height)];
        resultImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        //获取处理后图片的大小
        data = UIImageJPEGRepresentation(resultImage, compression);
    }
    
    return resultImage;
}