Painting a Gradient inside an Image by tapping in Objective-C? - ios

Question

I have an animal image and that image have a white background and the shape of animal is black outline. That is fixed on my image view in my .xib.
Now I would like to paint on the image, however only on the particular closed part.
Suppose a user touches on the hand then only hands will fill the gradient. The rest of the image will remain the same.
- (UIImage*)imageFromRawData:(unsigned char *)rawData
{
NSUInteger bitsPerComponent = 8;
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * self.imageDoodle.image.size.width;
CGImageRef imageRef = [self.imageDoodle.image CGImage];
CGColorSpaceRef colorSpace = CGImageGetColorSpace(imageRef);
CGContextRef context = CGBitmapContextCreate(rawData,self.imageDoodle.image.size.width,
self.imageDoodle.image.size.height,bitsPerComponent,bytesPerRow,colorSpace,
kCGImageAlphaPremultipliedLast);
imageRef = CGBitmapContextCreateImage (context);
UIImage* rawImage = [UIImage imageWithCGImage:imageRef];
CGContextRelease(context);
CGImageRelease(imageRef);
return rawImage;
}
-(unsigned char*)rawDataFromImage:(UIImage *)image
{
CGImageRef imageRef = [image CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
NSLog(#"w=%d,h=%d",width,height);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = malloc(height * width * 4);
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGContextRelease(context);
return rawData;
}
Where would I need to change my code to support this?
This is possible by UIBezierPath but I don't know how to implement it in this case.