10 Computer vision (OpenCV) Interview Questions and Answers for python engineers

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1. Can you describe your experience working with OpenCV and computer vision?

Throughout my career I have had the opportunity to work with OpenCV and computer vision, specifically in the realm of object detection and recognition. One of my notable projects involved developing a system for identifying and tracking vehicles on a busy highway.

  1. To start, I implemented a pre-processing pipeline for optimizing the images captured by the camera, which involved resizing, normalizing, and enhancing the contrast of the images.
  2. Next, I utilized various OpenCV functions to detect and extract features such as edges, corners, and contours from the images.
  3. Using these features, I then created a customized Haar Cascade classifier for vehicle detection, which achieved an accuracy of over 90%.
  4. To track the vehicles, I employed a combination of feature-based and template-based tracking algorithms, which allowed for real-time tracking with minimal latency.
  5. Finally, I integrated the system with a machine learning algorithm for vehicle recognition, which allowed for automatic identification of the make and model of each detected vehicle.

Overall, this project demonstrated my ability to effectively utilize OpenCV and computer vision techniques for real-world applications, resulting in a functional and accurate system for vehicle detection and recognition.

2. What image processing tasks have you previously accomplished with OpenCV?

I have accomplished various image processing tasks with OpenCV, some of which include:

  1. Object detection: I have used OpenCV to create object detection models that can accurately identify and classify objects in images. For example, I created a model that could accurately detect different types of fruits in images with an accuracy rate of over 95%.
  2. Face recognition: I have also used OpenCV to develop a facial recognition system that can recognize individuals with high accuracy rates. The system was trained on a dataset of over 1,000 faces and was able to correctly recognize individuals with a 90% accuracy rate.
  3. Image segmentation: Using OpenCV, I have also performed image segmentation tasks, which involves dividing an image into multiple segments or regions. For example, I segmented an image of a city skyline to identify the different buildings and landmarks in the image.
  4. Optical character recognition: I have used OpenCV to create an OCR system that can accurately recognize and extract text from images. The system was trained on a dataset of over 1,000 images and was able to correctly recognize over 80% of the text in the images.
  5. Image enhancement: Lastly, I have used OpenCV to enhance the quality of images, by adjusting the brightness and contrast, reducing noise, and sharpening the edges. For example, I improved the quality of a low-light image of a night sky, making the stars more visible without adding noise to the image.

In all of these projects, I was able to use OpenCV to efficiently and effectively perform complex image processing tasks, resulting in accurate and meaningful results.

3. Can you explain how OpenCV handles image processing and manipulation?

OpenCV is a powerful open-source computer vision library that provides a wide range of image processing and manipulation features. It is written in C++ and has interfaces for Python, Java, and C#.

  1. Reading and writing images: OpenCV provides functions for reading and writing various image formats, such as JPEG, PNG, and BMP. For example, imread() function is used to read an image and imwrite() function is used to write an image.
  2. Color conversion: OpenCV provides functions for converting images from one color space to another, such as RGB to grayscale or HSV to RGB. cvtColor() function is used for color conversion.
  3. Image enhancement: OpenCV provides functions for image enhancement, such as histogram equalization, image sharpening, and denoising. For example, equalizeHist() function is used for histogram equalization.
  4. Image smoothing: OpenCV provides functions for image smoothing, such as Gaussian blur and median blur.
  5. Image segmentation: OpenCV provides functions for image segmentation, such as thresholding and edge detection. For example, Canny() function is used for edge detection.
  6. Feature detection and description: OpenCV provides functions for detecting and describing features in images, such as keypoints and descriptors.
  7. Object detection: OpenCV provides functions for object detection, such as Haar cascades and HOG descriptors. For example, detectMultiscale() function is used for object detection using Haar cascades.
  8. Optical flow: OpenCV provides functions for optical flow, which is the movement of objects in successive frames. For example, calcOpticalFlowPyrLK() function is used for optical flow calculation.
  9. Image stitching: OpenCV provides functions for image stitching, which is the process of combining multiple images into a single panoramic image. For example, stitcher::stitch() function is used for image stitching.
  10. Machine learning: OpenCV provides functions for machine learning, such as support vector machines and neural networks.

Overall, OpenCV is an extremely versatile library for image processing and manipulation, with a wide range of features that can be used for various computer vision tasks such as object detection, image segmentation, and optical flow. Employing OpenCV in image processing could lead to noticeable improvements in image quality, and hence play a role in improving various industries such as medical science, security and surveillance, etc.

4. How familiar are you with different algorithms used in image processing and computer vision?

During my career, I have gained extensive knowledge and experience in different algorithms used in image processing and computer vision. I am confident in my ability to apply these algorithms in a practical setting, as demonstrated by my previous work at XYZ Company.

  1. One specific example of an algorithm I am familiar with is the Lucas-Kanade method for optical flow estimation. I used this algorithm as part of a project to develop a real-time object tracking system for autonomous drones. The final product achieved an accuracy rate of 95% in tracking moving objects, even in challenging lighting conditions.
  2. Another algorithm that I am familiar with is the Scale-Invariant Feature Transform (SIFT) algorithm, which I have used to develop a computer vision system for detecting and recognizing faces in images. The system achieved an accuracy rate of 98% in correctly identifying faces, even when they were partially obscured or in low-resolution images.
  3. I am also proficient in the use of the Viola-Jones object detection framework, which I have used to analyze video data from security cameras in a retail setting. The model was able to accurately detect and track shoppers in real-time and generate heat maps of store traffic to help optimize store layout and marketing strategies.
  4. In addition to these specific algorithms, I have experience working with various machine learning algorithms, including deep neural networks and decision trees, as part of my work on projects such as image classification and object recognition. I am constantly exploring new methods and techniques to stay up-to-date with the latest advancements in the field.

Overall, I am confident in my ability to apply different algorithms used in image processing and computer vision in practical settings, and I believe that my success in past projects is a testament to my proficiency in this area.

5. What types of projects have you worked on that required computer vision and what was your role in those projects?

During my time at XYZ company, I worked on several computer vision projects, ranging from object detection and recognition to image segmentation and processing.

  1. One notable project was an automated surveillance system for a large retail store. My role in the project was to develop algorithms for detecting suspicious behaviors and actions in real-time using CCTV cameras. By leveraging OpenCV and machine learning techniques, we were able to achieve a high accuracy rate and reduce the number of false positives, resulting in an effective and reliable system.
  2. Another project involved developing a gesture recognition interface for a virtual reality application. The goal was to enable users to interact with the virtual environment using hand gestures instead of a controller. I was responsible for designing and training Convolutional Neural Networks (CNNs) to recognize various hand gestures, such as pinch, swipe and grab. The system achieved an accuracy of 95% and received positive feedback from users during user testing.

In addition, I have also worked on image processing projects such as enhancing the quality of medical images for better diagnosis, segmenting images in autonomous driving applications, and analyzing satellite images for environmental monitoring. In each of these projects, I played a pivotal role in developing and implementing computer vision solutions to solve complex problems.

6. Can you walk me through a specific OpenCV implementation you've done in the past?

During my time at X Company, I implemented an OpenCV project that focused on object detection and tracking. The goal was to track a specific object in real-time video footage and accurately determine its position and motion.

  1. First, I used the OpenCV library to perform image processing and identify the object of interest using color segmentation techniques.

  2. Next, I utilized various algorithms for object tracking such as mean-shift, Kalman filters, and SVM classifiers to track the object through the frames.

  3. To improve the tracking accuracy, I also implemented feature extraction using SIFT and SURF techniques to better identify and follow the object.

  4. Finally, I displayed the results of the tracking on a graphical user interface, which visualized the object's path, speed, and acceleration.

The implementation achieved a tracking accuracy of over 95%, even when the object was occluded or partially hidden in the frame. We tested the system on a large video dataset that included a variety of challenging scenarios, including different lighting conditions and background clutter.

The project's success led to its integration into a larger system that was used for surveillance and security applications. Overall, this OpenCV implementation demonstrated my ability to develop complex computer vision systems that can solve real-world problems.

7. How do you approach debugging and troubleshooting issues with OpenCV code?

Debugging and troubleshooting issues with OpenCV code can be overwhelming, but I have developed a systematic process that has proven successful in resolving issues quickly.

  1. Reproduce the problem: The first step is to reproduce the problem to fully understand what is happening. I use different techniques such as adding log statements or running the code in debug mode to track the problematic segment of the code.
  2. Research: After identifying the problematic code, I then conduct extensive research online to gain knowledge on the issue. I search through different forums, StackOverflow, and the official OpenCV documentation to find a solution or related problems people had dealt with.
  3. Verify: Once a potential solution is found , I verify if it solves the issue. I test the corrected code on multiple inputs and compare the output with the expected result.
  4. Optimize: In an attempt to improve performance, I optimize the code by profiling, using different data structures or changing data types. For instance, I once optimized an OpenCV function to reduce its runtime by 30% by using a narrower data type for the input image.
  5. Document: Finally, I document the issue, the solution and the optimization done in case the issue occurs again or someone else experiences a similar problem. I create a troubleshooting document consisting of the steps I used to resolve the issue and store it in the company's repository.

Using this approach has helped me solve numerous issues such as segmentation faults caused by incorrect memory allocation or inconsistent results from the same input data.

For example, while working on a project that involved detecting traffic lights from a video stream, I encountered a problem with the color detection, where the color segmentation wasn't correctly detecting certain colors. Using the above approach, I was able to identify that the problematic color detection overfit the model to the specific dataset I was testing with. So I created a better, generalized model which showed a +10% increase in detection rate when testing with data external to the dataset.

8. What tools and techniques do you use to optimize the performance of OpenCV code?

When it comes to optimizing performance of OpenCV code, I rely on a number of tools and techniques that have helped me achieve impressive results. Here are a few examples:

  1. Profiling tools: To identify potential bottlenecks in my code, I often use profiling tools like gprof or Intel VTune. By examining the output metrics they provide, I'm able to pinpoint functions that are hogging resources or causing performance issues.
  2. Compiler optimization flags: I enable compiler optimization flags like -O3 to help the compiler generate more efficient code. This can result in significant performance gains without changing the code itself.
  3. Parallel processing: Some OpenCV algorithms lend themselves well to parallel processing, so I take advantage of multithreading or parallelization techniques like OpenMP to distribute work across multiple cores or threads. For example, by using multi-threading in the FACE RECOGNITION algorithm, I was able to see a 25% improvement in processing time.
  4. Memory management: I'm mindful of memory allocation and deallocation, and I use techniques like caching and memory reuse to minimize the overhead of memory allocation. For example, when working with large image data, I use specialized data structures like memory-mapped files that allow me to efficiently access data without incurring the cost of loading it all into memory.

Using a combination of these tools and techniques, I've been able to achieve impressive performance gains in my OpenCV code. For example, when optimizing my implementation of the ORB matching algorithm for real-time processing of streaming video, I achieved a frame-rate increase of over 20% and a resource utilization decrease of 35%.

9. Are you familiar with other computer vision libraries or platforms besides OpenCV?

I am definitely familiar with other computer vision libraries and platforms outside of OpenCV. In fact, I've had quite a bit of experience working with Tensorflow, which is an incredibly powerful platform for machine learning and computer vision applications. In a previous job, I was tasked with developing a computer vision system to detect and track objects in real-time using Tensorflow's object detection API.

  1. One of the major benefits of working with Tensorflow was its ability to handle large amounts of data. For example, when working with a dataset of several thousand images, Tensorflow was able to quickly and accurately process and classify each image.
  2. Another advantage of Tensorflow was its ease of use. Even though it was my first time working with the platform, I was quickly able to pick up on the programming language and syntax, which allowed me to develop a high-quality computer vision system in a relatively short amount of time.
  3. Lastly, I was impressed with Tensorflow's ability to integrate with other platforms and tools. For example, I was able to easily integrate Tensorflow with Docker containers and AWS cloud services to distribute my computer vision application across multiple servers, which drastically improved its performance and accuracy.

Overall, while I may be most familiar with OpenCV for computer vision applications, I am confident in my ability to work with other platforms, such as Tensorflow, depending on the specific needs of the job or project.

10. Can you provide an example of how you've implemented machine learning techniques with OpenCV?

Yes, I have implemented machine learning techniques with OpenCV in a project that involved object detection and tracking. Specifically, I used the Haar Cascade Classifier to detect and track cars in a live video stream.

  1. To begin, I collected a dataset of images containing various types of cars and annotated them with bounding boxes using labelImg.
  2. Next, I used OpenCV to train a Haar Cascade Classifier on the annotated images. I utilized the cv2.CascadeClassifier method to create the classifier and cv2.detectMultiscale to detect the cars in the video stream.
  3. To track the detected cars, I used the Kalman Filter algorithm. I implemented this algorithm using the cv2.KalmanFilter method in OpenCV.
  4. After implementing the object detection and tracking pipeline, I evaluated the performance of the system. I measured the accuracy of the object detection and tracking using metrics such as precision, recall, and F1-score. The results showed that the system performed with high accuracy and achieved an F1-score of 0.93.

Overall, this project demonstrated my ability to utilize machine learning techniques with OpenCV for object detection and tracking in real-time. It also showcased my proficiency in implementing and evaluating computer vision models.


Congratulations on learning about the top 10 Computer Vision (OpenCV) interview questions and answers for 2023. Now that you have prepared for your interview, the next step is to showcase your skills and stand out from other applicants. Don't forget to write a compelling cover letter that highlights your accomplishments and skills to catch the attention of potential employers. Our guide on writing a cover letter can offer additional tips and guidance to help you craft the perfect cover letter. Additionally, having an impressive CV is crucial to making a good first impression. Our guide on writing a resume for python engineers can help you create a polished and professional resume that highlights your experience and skills. If you're ready to take the next step in your career search, Remote Rocketship is the perfect place to find remote Python Engineer jobs. Check out our job board at https://www.remoterocketship.com/jobs/backend-developer and find your dream job today!

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