I’m working on resizing the nose on a facial image using OpenCV in Objective-C++ for iOS. The goal is to elongate or shorten the nose, but my current implementation only modifies a cropped area, which is then overlaid back onto the original image rather than adjusting the nose size directly on the face. Here is the snippet from my OpenCVWrapper.mm:

+ (UIImage *)makeNoseLongerInImage:(UIImage *)image withFactor:(int)scaleFactor {
    cv::Mat mat;
    [image convertToMat:&mat :false];

    NSString *path = [[NSBundle mainBundle] pathForResource:@"haarcascade_frontalface_default" ofType:@"xml"];
    cv::CascadeClassifier face_cascade;
    if (!face_cascade.load([path UTF8String])) {
        NSLog(@"Failed to load face cascade from path: %@", path);
        return image;
    }

    std::vector<cv::Rect> faces;
    face_cascade.detectMultiScale(mat, faces, 1.1, 2, 0 | cv::CASCADE_SCALE_IMAGE, cv::Size(30, 30));

    for (const cv::Rect& face : faces) {
        cv::Rect noseArea(
            std::max(0, face.x + static_cast<int>(face.width * 0.25)),
            std::max(0, face.y + static_cast<int>(face.height * 0.60)),
            std::min(mat.cols - face.x, static_cast<int>(face.width * 0.50)),
            std::min(mat.rows - face.y, static_cast<int>(face.height * 0.12))
        );

        if (noseArea.width == 0 || noseArea.height == 0) {
            NSLog(@"nose area computed with zero width or height.");
            continue;
        }

        cv::Mat noseRegion = mat(noseArea);
        int newHeight = std::max(1, static_cast<int>(noseRegion.rows * scaleFactor / 100.0));
        cv::Mat resizednoseRegion;
        cv::resize(noseRegion, resizednoseRegion, cv::Size(noseRegion.cols, newHeight), 0, 0, cv::INTER_LINEAR);

        NSLog(@"Original nose region: (%d, %d), Resized: (%d, %d)", noseRegion.cols, noseRegion.rows, resizednoseRegion.cols, resizednoseRegion.rows);

        // Place the resized nose region back into the original mat
        if (!resizednoseRegion.empty() && resizednoseRegion.cols == noseRegion.cols && resizednoseRegion.rows == newHeight) {
            // Update the noseArea to match the resized dimensions
            cv::Rect newnoseArea = noseArea;
            newnoseArea.height = newHeight; // Update height to match resized region
            resizednoseRegion.copyTo(mat(newnoseArea));
        } else {
            NSLog(@"Mismatch in dimensions after resize or empty resized region.");
        }
    }

    return MatToUIImage(mat);
}