With the following code the image showed as above is converted as below image... Their it's showing black background with gray lines.....i want white background with gray lines .. Please guide me .. i am new to iPhone Thanks alot in Advance - (void)viewDidLoad { [super viewDidLoad]; // Initialise video capture - only supported on iOS device NOT simulator #if TARGET_IPHONE_SIMULATOR NSLog(@"Video capture is not supported in the simulator"); #else _videoCapture = new cv::VideoCapture; if (!_videoCapture->open(CV_CAP_AVFOUNDATION)) { NSLog(@"Failed to open video camera"); } #endif // Load a test image and demonstrate conversion between UIImage and cv::Mat UIImage *testImage = [UIImage imageNamed:@"testimage.jpg"]; double t; int times = 10; //-------------------------------- // Convert from UIImage to cv::Mat NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; t = (double)cv::getTickCount(); for (int i = 0; i < times; i++) { cv::Mat tempMat = [testImage CVMat]; } t = 1000 * ((double)cv::getTickCount() - t) / cv::getTickFrequency() / times; [pool release]; NSLog(@"UIImage to cv::Mat: %gms", t); //------------------------------------------ // Convert from UIImage to grayscale cv::Mat pool = [[NSAutoreleasePool alloc] init]; t = (double)cv::getTickCount(); for (int i = 0; i < times; i++) { cv::Mat tempMat = [testImage CVGrayscaleMat]; } t = 1000 * ((double)cv::getTickCount() - t) / cv::getTickFrequency() / times; [pool release]; NSLog(@"UIImage to grayscale cv::Mat: %gms", t); //-------------------------------- // Convert from cv::Mat to UIImage cv::Mat testMat = [testImage CVMat]; t = (double)cv::getTickCount(); for (int i = 0; i < times; i++) { UIImage *tempImage = [[UIImage alloc] initWithCVMat:testMat]; [tempImage release]; } t = 1000 * ((double)cv::getTickCount() - t) / cv::getTickFrequency() / times; NSLog(@"cv::Mat to UIImage: %gms", t); // Process test image and force update of UI _lastFrame = testMat; [self sliderChanged:nil]; } - (IBAction)capture:(id)sender { if (_videoCapture && _videoCapture->grab()) { (*_videoCapture) >> _lastFrame; [self processFrame]; } else { NSLog(@"Failed to grab frame"); } } - (void)processFrame { double t = (double)cv::getTickCount(); cv::Mat grayFrame, output; // Convert captured frame to grayscale cv::cvtColor(_lastFrame, grayFrame, cv::COLOR_RGB2GRAY); // Perform Canny edge detection using slide values for thresholds cv::Canny(grayFrame, output, _lowSlider.value * kCannyAperture * kCannyAperture, _highSlider.value * kCannyAperture * kCannyAperture, kCannyAperture); t = 1000 * ((double)cv::getTickCount() - t) / cv::getTickFrequency(); // Display result self.imageView.image = [UIImage imageWithCVMat:output]; self.elapsedTimeLabel.text = [NSString stringWithFormat:@"%.1fms", t]; }