iOS 获取图片、区域的主色。水印文字颜色处理。

//添加水印
+ (UIImage *)getWaterMarkWith:(UIImage *)image waterText:(NSString *)str{
    
    CGSize imageSize = image.size;
    CGFloat imageWidth = imageSize.width;
    CGFloat imageHeight = imageSize.height;
    
    UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0);
    [image drawAtPoint:CGPointZero];
    CGFloat textFont = 10 * ceilf(imageWidth / [UIScreen mainScreen].bounds.size.width);
    CGSize perSize = [self getSize:imageWidth font:[UIFont systemFontOfSize:textFont] str:str lineSpace:0];
    CGRect rect = CGRectMake(ceilf(imageWidth - perSize.width - 20),
                             ceilf(imageHeight - perSize.height - 20),
                             ceilf(perSize.width + 10),
                             ceilf(perSize.height + 5));
    
    NSDictionary *colorInfo = [self mostColor:image scale:1 rect:rect];
    CGFloat red = [colorInfo[@"red"] floatValue];
    CGFloat green = [colorInfo[@"green"] floatValue];
    CGFloat blue = [colorInfo[@"blue"] floatValue];
    CGFloat alpha = [colorInfo[@"alpha"] floatValue];
    BOOL colorDark = [self isDarkColor:[UIColor colorWithRed:red green:green blue:blue alpha:alpha]];
    [str drawAtPoint:rect.origin withAttributes:@{NSFontAttributeName:[UIFont systemFontOfSize:textFont], NSForegroundColorAttributeName:colorDark ? [UIColor whiteColor] : [UIColor blackColor]}];
    image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return image;
}

// 获取图片、区域的主色
+ (NSDictionary *)mostColor:(UIImage *)image scale:(CGFloat)scale rect:(CGRect)rect{
    
#if __IPHONE_OS_VERSION_MAX_ALLOWED > __IPHONE_6_1
    int bitmapInfo = kCGBitmapByteOrderDefault | kCGImageAlphaPremultipliedLast;
#else
    int bitmapInfo = kCGImageAlphaPremultipliedLast;
#endif
    if (scale <= 0.1) {
        scale = 0.1;
    }else if(scale >= 1){
        scale = 1;
    }
    
    if (rect.size.width > 0 && rect.size.height > 0) {
        image = [self cropSquareImage:image rect:rect];
    }
    
    //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([image size].width * scale, [image size].height * scale);
    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, image.CGImage);
    CGColorSpaceRelease(colorSpace);
    
    //第二步 取每个点的像素值
    unsigned char* data = CGBitmapContextGetData (context);
    
    if (data == NULL){
        CGContextRelease(context);
        return nil;
    }
    
    NSCountedSet *cls = [NSCountedSet setWithCapacity:thumbSize.width*thumbSize.height];
    
    for (int x=0; x<thumbSize.height; x++) {
        for (int y=0; y<thumbSize.width; y++) {
            int offset = 4*(x*thumbSize.width + y);
            int red = data[offset];
            int green = data[offset+1];
            int blue = data[offset+2];
            int alpha =  data[offset+3];
            
            NSArray *clr=@[@(red),@(green),@(blue),@(alpha)];
            [cls addObject:clr];
        }
    }
    CGContextRelease(context);

    //第三步 找到出现次数最多的那个颜色
    NSEnumerator *enumerator = [cls objectEnumerator];
    NSArray *curColor = nil;
    
    NSArray *MaxColor=nil;
    NSUInteger MaxCount=0;
    
    while ( (curColor = [enumerator nextObject]) != nil ){
        NSUInteger tmpCount = [cls countForObject:curColor];
        if ( tmpCount < MaxCount ) continue;
        MaxCount=tmpCount;
        MaxColor=curColor;
    }
    //返回三色值+透明度
    NSMutableDictionary *dic = [[NSMutableDictionary alloc] initWithCapacity:0];
    [dic setValue:@([MaxColor[0] intValue]/255.0f) forKey:@"red"];
    [dic setValue:@([MaxColor[1] intValue]/255.0f) forKey:@"green"];
    [dic setValue:@([MaxColor[2] intValue]/255.0f) forKey:@"blue"];
    [dic setValue:@([MaxColor[3] intValue]/255.0f) forKey:@"alpha"];
    return dic;
}
//裁剪图片
+ (UIImage *)cropSquareImage:(UIImage *)image rect:(CGRect)rect{
    CGImageRef sourceImageRef = [image CGImage];
    CGImageRef newImageRef = CGImageCreateWithImageInRect(sourceImageRef, rect);
    UIImage *newImage = [UIImage imageWithCGImage:newImageRef];
    return newImage;
}


//判断颜色深浅
+ (BOOL)isDarkColor:(UIColor *)newColor{
    const CGFloat *componentColors = CGColorGetComponents(newColor.CGColor);
    CGFloat colorBrightness = ((componentColors[0] * 299) + (componentColors[1] * 587) + (componentColors[2] * 114)) / 1000;
    if (colorBrightness < 0.5){
        //深色
        return YES;
    } else{
        //浅色
        return NO;
    }
}

主要方法来自其他文档，自己再修改整合。