Black & White of the image + iphone

UIImage *originalImage = rgbImg.image; // this image we get from UIImagePickerController
    CGColorSpaceRef colorSapce = CGColorSpaceCreateDeviceGray();
    CGContextRef context = CGBitmapContextCreate(nil, originalImage.size.width, originalImage.size.height, 8, originalImage.size.width, colorSapce, kCGImageAlphaNone);
    CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
    CGContextSetShouldAntialias(context, NO);
    CGContextDrawImage(context, CGRectMake(0, 0, originalImage.size.width, originalImage.size.height), [originalImage CGImage]);
    CGImageRef bwImage = CGBitmapContextCreateImage(context);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSapce);
    rgbImg.image = [UIImage imageWithCGImage:bwImage]; // This is result B/W image.
    CGImageRelease(bwImage);