Count pixels in an irregular shape - objective-c

Question

I have an existing app, written in Obj C, that works and is on the iTunes App Store. I am updating it to Swift. I am having trouble with the pixel classification and counting portion of the app. The Objective C code is below: I would appreciate any suggestions as how to proceed with the Swift 3 version.
void classifyPixel(unsigned char r, unsigned char g, unsigned char b,
NSUInteger *coverRed, NSUInteger *coverGreen, NSUInteger *coverYellow, NSUInteger *coverBlue, NSUInteger *coverWhite)
{
if ((r == 255) && (g == 0) && (b == 0))
*coverRed = *coverRed + 1;
else if ((r == 0) && (g == 255) && (b == 0))
*coverGreen = *coverGreen + 1;
else if ((r == 255) && (g == 255) && (b == 0))
*coverYellow = *coverYellow +1;
else if ((r == 0) && (g == 0) && (b== 255))
*coverBlue = *coverBlue + 1;
else if ((r == 255) & (g == 255) && (b == 255))
*coverWhite = *coverWhite +1;
}
- (IBAction)computeArea:(id)sender {
// Taken from Hugh's original code. With some slight clean up
UIImage *image = self.imageView.image;
NSUInteger coverRed = 0;
NSUInteger coverGreen = 0;
NSUInteger coverYellow = 0;
NSUInteger coverBlue = 0;
NSUInteger coverWhite = 0;
NSUInteger coverTotal = 0;
size_t image_width = image.size.width;
size_t image_height = image.size.height;
size_t bitsPerComponent = 8;
size_t bytesPerPixel = 4;
size_t bytesPerRow = bytesPerPixel*image_width;
unsigned char* raster_buffer = (unsigned char*) calloc(bitsPerComponent, bytesPerRow *image.size.height);
if(raster_buffer !=NULL)
{
CGContextRef context = CGBitmapContextCreate(
(void*) raster_buffer,
image.size.width,
image.size.height,
bitsPerComponent,
bytesPerRow,
CGImageGetColorSpace(image.CGImage),
(CGBitmapInfo)kCGImageAlphaPremultipliedLast);
if (context != NULL)
{
CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, image.size.width, image.size.height), image.CGImage);
unsigned char* row_start_p = raster_buffer;
for (size_t y=0; y<image_height; y++)
{
unsigned char* nth_pixel_p = row_start_p;
for (size_t x=0; x<image_width; x++)
{
classifyPixel(nth_pixel_p[bytesPerPixel*x],
nth_pixel_p[bytesPerPixel*x+1],
nth_pixel_p[bytesPerPixel*x+2],
&coverRed,&coverGreen,&coverYellow,&coverBlue,&coverWhite);
coverTotal++;
}
row_start_p+=bytesPerRow;
}
}
}
free(raster_buffer);
float uu = coverGreen;
float vv = coverYellow;
float ww = coverRed;
float xx = coverBlue;
float yy = coverWhite;
float zz = uu + vv + ww + xx + yy;
float aa = (uu/zz)*100;
float bb = (vv/zz)*100;
float cc = (ww/zz)*100;
float dd = (xx/zz)*100;
float ee = (yy/zz)*100;
totalcount = [NSNumber numberWithFloat:zz];
greencountresult = [NSString stringWithFormat:#"%.1f%%",aa];
yellowcountresult = [NSString stringWithFormat:#"%.1f%%",bb];
redcountresult = [NSString stringWithFormat:#"%.1f%%",cc];
bluecountresult = [NSString stringWithFormat:#"%.1f%%",dd];
whitecountresult = [NSString stringWithFormat:#"%.1f%%",ee];
NSLog(#"Area compute! Red %lu Green %lu Yellow %lu Blue %lu White %lu\n",(unsigned long)coverRed,(unsigned long)coverGreen,(unsigned long)coverYellow,(unsigned long)coverBlue,(unsigned long)coverWhite);
}