iOS获取图片UIImage颜色均值AverageColor

在iOS判断颜色UIColor是浅色还是深色(DarkOrBright))中介绍了对颜色深浅的判断。那么，假如要判断背景图片颜色的深浅又该如何做呢？这里接啥一个获取UIImage颜色均值的方法，结合上一篇博文，便能很好的判断图片深浅：

- (UIColor )averageColorForImage:(UIImage)image {
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    unsigned char rgba[4];
    CGContextRef context = CGBitmapContextCreate(rgba, 1, 1, 8, 4, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGContextDrawImage(context, CGRectMake(0, 0, 1, 1), image.CGImage);
CGColorSpaceRelease(colorSpace);
CGContextRelease(context);

if(rgba[3] > 0) {
    CGFloat alpha = ((CGFloat)rgba[3])/255.0;
    CGFloat multiplier = alpha/255.0;
    return [UIColor colorWithRed:((CGFloat)rgba[0])*multiplier
                           green:((CGFloat)rgba[1])*multiplier
                            blue:((CGFloat)rgba[2])*multiplier
                           alpha:alpha];
}
else {
    return [UIColor colorWithRed:((CGFloat)rgba[0])/255.0
                           green:((CGFloat)rgba[1])/255.0
                            blue:((CGFloat)rgba[2])/255.0
                           alpha:((CGFloat)rgba[3])/255.0];
}
}