for(int x=xStart;x<xEnde;x=x+2) {
                for(int y=yStart;y<yEnde;y=y+2) {
                    color = [bitmapRep colorAtX:x y:y];
                    sumRed   += color.redComponent;
                    sumGreen += color.greenComponent;
                    sumBlue  += color.blueComponent;
                    counter++;
                    if(y==yStart || yEnde-y < 2) // Das ist nur zur Visualisierung drin
                        [bitmapRep setColor:[NSColor blueColor] atX:x y:y];
                    else
                        [bitmapRep setColor:[NSColor redColor] atX:x y:y];
                }
            }

unsigned short* destData = (unsigned short*) [bitmapRep bitmapData];
    
    for(int i=0;i<sizeof(destData);i++) {
        NSLog(@"%c",destData[i]);
    }
    

    NSArray             *inputReps = [NSBitmapImageRep imageRepsWithContentsOfFile: @"/PathToFile"];
    NSBitmapImageRep    *sourceRep, *scanRep;
    NSGraphicsContext   *bitmapContext;
    NSInteger           width, height, x, y, pixelCount;
    unsigned char       *p, *pLine;
    unsigned long long  rSum, gSum, bSum;
    struct timeval      before, after;
    
    sourceRep = [inputReps objectAtIndex: 0];
    width = [sourceRep pixelsWide];
    height = [sourceRep pixelsHigh];
    scanRep = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes: NULL
                                                      pixelsWide: width
                                                      pixelsHigh: height 
                                                   bitsPerSample: 8
                                                 samplesPerPixel: 4
                                                        hasAlpha: YES
                                                        isPlanar: NO
                                                  colorSpaceName: NSCalibratedRGBColorSpace
                                                     bytesPerRow: 0
                                                    bitsPerPixel: 0];
    
    bitmapContext = [NSGraphicsContext graphicsContextWithBitmapImageRep: scanRep];
    [NSGraphicsContext saveGraphicsState];
    [NSGraphicsContext setCurrentContext: bitmapContext];
    [sourceRep drawInRect: NSMakeRect(0.0, 0.0, (CGFloat)width, (CGFloat)height)];
    [NSGraphicsContext restoreGraphicsState];
    
    pLine = (unsigned char*)[scanRep bitmapData];
    rSum = 0;
    gSum = 0;
    bSum = 0;
    pixelCount = 0;
    gettimeofday(&before, NULL);
    for (y = 0; y < height; y++) {
       p = pLine;
        for (x = 0; x < width; x++) {
            rSum += *p++;
            gSum += *p++;
            bSum += *p++;
            p++;
            pixelCount++;
        }
        pLine += [scanRep bytesPerRow];
    }
    gettimeofday(&after, NULL);
    [scanRep release];
    NSLog(@"Average color: (%f, %f, %f) (%lld pixels)\n", (double)rSum / 256.0 / (double)pixelCount,
          (double)gSum / 256.0 / (double)pixelCount,( double)bSum / 256.0 / (double)pixelCount,
          (long long)pixelCount);
    NSLog(@"Time: %f s\n", after.tv_sec - before.tv_sec + (after.tv_usec - before.tv_usec) / 1000000.0);