Reverse Image Masking - ios

Question

In IOS SDK, I am able to mask an image but not able to reverse image mask. i mean, i have one make image which have rectangle part and now i mask image and i get attached image but i want reverse result.
I get image as result.
while i need this as result.
Please help me to achieve it.
...Edit...
My code
UIGraphicsBeginImageContextWithOptions(self.imageView.frame.size, NO, 0.0);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, 0.0, self.imageView.frame.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
CGImageRef maskImage = [[UIImage imageNamed:#"2.png"] CGImage];
CGContextClipToMask(context, self.imageView.bounds, maskImage);
CGContextTranslateCTM(context, 0.0, self.imageView.frame.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
[[self.imageView image] drawInRect:self.imageView.bounds];
UIImage *image11 = UIGraphicsGetImageFromCurrentImageContext();
self.imageView.image = image11;
Thanks

Answer 1

I have achieved it in two steps. May not be the best way to do it, but it works.
Invert your mask Image.
Mask
Look at the code below.
- (void)viewDidLoad
{
[super viewDidLoad];
_imageView = [[UIImageView alloc] initWithImage:i(#"test1.jpg")];
_imageView.image = [self maskImage:i(#"face.jpg") withMask:[self negativeImage]];
[self.view addSubview:_imageView];
}
The method below is taken from here
- (UIImage *)negativeImage
{
// get width and height as integers, since we'll be using them as
// array subscripts, etc, and this'll save a whole lot of casting
CGSize size = self.imageView.frame.size;
int width = size.width;
int height = size.height;
// Create a suitable RGB+alpha bitmap context in BGRA colour space
CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *memoryPool = (unsigned char *)calloc(width*height*4, 1);
CGContextRef context = CGBitmapContextCreate(memoryPool, width, height, 8, width * 4, colourSpace, kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast);
CGColorSpaceRelease(colourSpace);
// draw the current image to the newly created context
CGContextDrawImage(context, CGRectMake(0, 0, width, height), [self.imageView.image CGImage]);
// run through every pixel, a scan line at a time...
for(int y = 0; y < height; y++)
{
// get a pointer to the start of this scan line
unsigned char *linePointer = &memoryPool[y * width * 4];
// step through the pixels one by one...
for(int x = 0; x < width; x++)
{
// get RGB values. We're dealing with premultiplied alpha
// here, so we need to divide by the alpha channel (if it
// isn't zero, of course) to get uninflected RGB. We
// multiply by 255 to keep precision while still using
// integers
int r, g, b;
if(linePointer[3])
{
r = linePointer[0] * 255 / linePointer[3];
g = linePointer[1] * 255 / linePointer[3];
b = linePointer[2] * 255 / linePointer[3];
}
else
r = g = b = 0;
// perform the colour inversion
r = 255 - r;
g = 255 - g;
b = 255 - b;
// multiply by alpha again, divide by 255 to undo the
// scaling before, store the new values and advance
// the pointer we're reading pixel data from
linePointer[0] = r * linePointer[3] / 255;
linePointer[1] = g * linePointer[3] / 255;
linePointer[2] = b * linePointer[3] / 255;
linePointer += 4;
}
}
// get a CG image from the context, wrap that into a
// UIImage
CGImageRef cgImage = CGBitmapContextCreateImage(context);
UIImage *returnImage = [UIImage imageWithCGImage:cgImage];
// clean up
CGImageRelease(cgImage);
CGContextRelease(context);
free(memoryPool);
// and return
return returnImage;
}
The method below taken from here.
- (UIImage*) maskImage:(UIImage *)image withMask:(UIImage *)maskImage {
CGImageRef maskRef = maskImage.CGImage;
CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef),
CGImageGetHeight(maskRef),
CGImageGetBitsPerComponent(maskRef),
CGImageGetBitsPerPixel(maskRef),
CGImageGetBytesPerRow(maskRef),
CGImageGetDataProvider(maskRef), NULL, false);
CGImageRef masked = CGImageCreateWithMask([image CGImage], mask);
return [UIImage imageWithCGImage:masked];
}