获取图片主色调

-(UIColor*)mostColor{
#if __IPHONE_OS_VERSION_MAX_ALLOWED > __IPHONE_6_1
    int bitmapInfo = kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedLast;
#else
    int bitmapInfo = kCGImageAlphaPremultipliedLast;
#endif
    //第一步 先把图片缩小 加快计算速度. 但越小结果误差可能越大
    CGSize thumbSize=CGSizeMake(50, 50);
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(NULL,
                                                 thumbSize.width,
                                                 thumbSize.height,
                                                 8,//bits per component
                                                 thumbSize.width*4,
                                                 colorSpace,
                                                 bitmapInfo);
     
    CGRect drawRect = CGRectMake(0, 0, thumbSize.width, thumbSize.height);
    CGContextDrawImage(context, drawRect, self.CGImage);
    CGColorSpaceRelease(colorSpace); 
    //第二步 取每个点的像素值
    unsigned char* data = CGBitmapContextGetData (context);
    if (data == NULL) return nil;
    NSCountedSet *cls=[NSCountedSet setWithCapacity:thumbSize.width*thumbSize.height];
    for (int x=0; x