HAColorFinder.m

//Divide up the work among workers
NSUInteger numberOfWorkers = 4;
NSUInteger pixelsPerWorker = pixelCount/numberOfWorkers;

for (NSUInteger worker = 0; worker < numberOfWorkers; worker++) {
    
    //Submit work blocks to be executed concurrently
    dispatch_async(weakMe.concurrentQueue, ^{
        
        //Add the colors result to a trie data strucuture whose leaf is the counter, O(1) baby
        HATrie *trie = [[HATrie alloc] init];
        
        //Get the pixels to work on
        NSUInteger workerOffset = worker * pixelsPerWorker;
        
        UInt32 * workerPixels;
        workerPixels = (UInt32 *) calloc(pixelsPerWorker, sizeof(UInt32));
        memcpy(workerPixels, pixels + workerOffset, pixelsPerWorker);
        
        //Loop over the pixels of interest
        UInt32 * currentPixel = workerPixels;
        for (NSUInteger j = 0; j < pixelsPerWorker; j++) {
            UInt32 color = *currentPixel;

            float red = R(color);
            float green = G(color);
            float blue = B(color);
            if ((red == 0 && green == 0 && blue == 0) || (red == 1 && green == 1 && blue == 1)) {
                continue;
            }

            HAColorComponents *components = [[HAColorComponents alloc] initWithRed:red green:green blue:blue];
            [trie addColorComponents:components];

            currentPixel++;
        }
        
        HAColorComponentsCount *maxColorComponentsCount = trie.maxCountColorComponents;
        [workerResults setObject:maxColorComponentsCount forKey:@(worker)];
    });
}