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Top 50 OpenCV interview questions and answers

Spread the Knowledge
OpenCV interview questions and answers

1) Explain what is OpenCV?

OpenCV stands for Open Source Computer Vision Library is an open-source library using which is used to develop real-time computer vision applications such as image processing, video capture, and analysis, for example, face detection and object detection.

2) List some application of OpenCV?

Some of the applications of OpenCV are object detection, face recognition, medical diagnosis, etc.

3) For what sobel operation is used in OpenCV?

In OpenCV Sobel Operator is a discrete differentiation operator which is used for image processing, basically, it combines Gaussian smoothing and differentiation.

4) What are Erosion and Dilation in OpenCv?

In OpenCV, Erosion and Dilation are the two very common morphological image processing operations which is a procedure for modifying the geometric structure in the image.

5) Which language is best for OpenCV?

C/C++ language is best for OpenCV.

6) Which method of opencv is used to read image?

The cv2.imread() method of the Imgcodecs class is used in OpenCV to read an image.


7) How to install OpenCV for Python in Windows?

We can install OpenCV for Python in Windows by performing the following steps:

Below Python packages are to be downloaded and installed to their default locations.

Python 3.x (3.4+) or Python 2.7.x from here. Numpy package (for example, using pip install numpy command). Matplotlib (pip install matplotlib) (Matplotlib is optional, but recommended since we use it a lot in our tutorials). Install all packages into their default locations.

Python will be installed to C:/Python27/ in case of Python 2.7. After installation, open Python IDLE. Enter import numpy and make sure Numpy is working fine.

Download the latest OpenCV release from GitHub or SourceForge site and double-click to extract it. Goto opencv/build/python/2.7 folder. Copy cv2.pyd to C:/Python27/lib/site-packages. Open Python IDLE and type the following codes in the Python terminal. >>> import cv2 as cv >>> print( cv.__version__ )

8) How many types of image filters available in OpenCV ?

There are two types of image filters available in OpenCV:

  • Linear filter
  • Non-linear filter

9) What is OpenGL?

OpenGL stands for Open Graphics Library, it is an open-source cross-platform application programming interface (API) for rendering 2D and 3D vector graphics. The API used to interact with GPU for achieving the hardware-accelerated rendering.

10) What is CUDA?

CUDA is a parallel computing platform developed by Nvidia that is consists of its own GPU for general computing.

11) Where opencv libraries are installed?

The OpenCV libraries will be installed in the /usr/local directory.

12) In OpenCV which function is used to draw line?

In OpenCV line() function is used to draw the line.

13) How many types of video filters in OpenCV?

Different types of video filters available in OpenCV are Blurring, Smoothing, Distortion, Warp Stabilizer, alpha extract, bilateral, color matrix, chrome hold, etc.

14) How to find threshold in images using OpenCV?

We can find the threshold of an image in OpenCV with the help of cv.threshold function.

15) What is Scharr Operator?

Scharr() Operator is an operator that is used to detect the second derivatives of an image in horizontal and vertical directions.

16) Which method of opencv is used to save image?

cv2.imwrite() method is the method of OpenCV that is used to save an image.

17) Which method of opencv is used to show image?

cv2.imshow() method is the method of OpenCV that is used to show an image.

18) Where opencv libraries are installed?

The libraries of the OpenCV are installed in the folder /usr/lib in the ubuntu and directly under the lib folder present in your OpenCV directory on Windows.

19) What is cv_8uc1 in opencv?

cv_8uc1 is an 8-bit single-channel array. It has 2 parts, the depth, and various numbers of channels. There is a flexible system that is enough to let the users define some new types with up to 215 channels. CV_8UC1 makes the code more clear that how many numbers of channels is the code is working with. If someone is dealing with a matrix that contains 10 channels or even more than that, the person needs to specify the number of channels that will be included.

20) Enlist different types of filters available in OpenCV?

The different types of linear and non-linear filter that you can apply to a picture using OpenCV are, BaeColumn filter, Base filter, BaseRow filter, FilterEngine, Bilateral filter, AdaptiveBilateral Filter, Blur, BorderInterpolate, BoxFilter, BuildPyramid, copyMakeBorder, createBoxFilter, createDerivFilter, createGuassionFilter, createLinear filter, createMorphology filter, createSeparableLinear filter, dilate, erode, filter2D, GuassianBlur, getDerivKernels, getKernelType, getStructuringElement, medianBlur, morphologyEx, Laplacian, pyrDown, pyrUp, pyrMeanShiftFiltering, sepFilter2D, Smooth, Sobel, Scharr.

21) What is computer vision ?

It’s Subset of AI. Computer vision is an interdisciplinary scientific field that deals with how computers can be made to gain high-level understanding from images or videos

22) What are languages supported by Computer vision ?

C++, Python, Matlab,

23)What are computer vision libraries ?

OpenCV – python, Java

24) How many algorithms in opencv ?

2500 optimized algorithms

25) What are machine learning algorithms available in opencv ?

  • Normal Bayes Classifier
  • K-Nearest Neighbors
  • Support Vector Machines
  • Decision Trees
  • Boosting
  • Gradient Boosted Trees
  • Random Trees
  • Extremely randomized trees

26) How many types of image filters in OpenCV ?

  • Averaging
  • Gaussian Filtering
  • Median Filtering
  • Bilateral Filtering

27) How many types of video filters in OpenCV ?

  • Color Conversion
  • Thresholding
  • Smoothing
  • Morphology Gradients Canny
  • Edge
  • Detection
  • Contours
  • Histograms

28) How can we Increase the Quality of an Image?

Image enhancement process is purely dependent on the application where we need to use the enhanced image and the type of degradation in the image. Few solutions from my basic knowledge

– If image contain so much noises, apply filtering operations such as mean/median etc.

– If the image is looking too dark or too bright apply histogram equalization process to improve the contrast.

– If the image is blurred apply sharpening operations in the image.

29) What Is Image Transform?

An image can be expanded in terms of a discrete set of basis arrays called basis images. Hence, these basis images can be generated by unitary matrices. An NxN image can be viewed as an N^2×1 vectors. It provides a set of coordinates or basis vectors for vector space.

30) What Do You Meant By Zooming Of Digital Images?

Zooming may be viewed as over sampling. Zooming involves the creation of new pixel locations and the assignment of gray levels to those new locations.

31) What Is The Need For Transform?

The need for transform is most of the signals or images are time domain signal (ie) signals can be measured with a function of time. This representation is not always best. Any person of the mathematical transformations is applied to the signal or images to obtain further information from that signal. Particularly, for image processing.

32) List The Hardware Oriented Color Models?

They are as follows.

– RGB model

– CMY model

– YIQ model

– HSI model

33) Do You Know What Rectification Is In Image Processing?

They are as follows.

– Rectification in Image Processing is a transformation process used to project two-or-more images onto a common image plane.

– It corrects image distortion by transforming the image into a standard coordinate system.

– It is used in computer stereo vision to simplify the problem of finding matching points between images.

– It is used in geographic information systems to merge images taken from multiple perspectives into a common map coordinate system.

34) What Is Meant By Illumination And Reflectance?

Illumination is the amount of source light incident on the scene. It is represented as i(x, y). Whereas, Reflectance is the amount of light reflected by the object on the scene. It is represented by r(x, y).

35) List The Categories Of Digital Storage?

They are as follows

– Short term storage for use during processing.

– Online storage for relatively fast recall.

– Archival storage for infrequent access.

36) What Are The Differences Between Structural Patterns & Morphological Structural Element?

In software engineering, structural design patterns are design patterns that ease the design by identifying a simple way to realize relationships between entities.

37) Write Short Notes On Neighbours Of A Pixel?

They are follows.

– The pixel p at co-ordinates (x, y) has 4 neighbors (ie) 2 horizontal and 2 vertical neighbors whose co-ordinates is given by (x+1, y), (x-1,y), (x,y-1), (x, y+1). This is called as direct neighbors. It is denoted by N4(P)

– Four diagonal neighbors of p have co-ordinates (x+1, y+1), (x+1,y-1), (x-1, y-1),(x-1, y+1). It is denoted by ND(4).
– Is a combination of 4 direct neighbors and 4 diagonal neighbors. Eight neighbors of p denoted by N8(P)

38) Define Resolutions?

Resolution is defined as the smallest number of discernible detail in an image.Spatial resolution is the smallest discernible detail in an image and gray level resolution refers to the smallest discernible change is gray level.

39) What Is Image Translation And Scaling?

Image translation means reposition the image from one co-ordinate location to another along straight line path. Whereas, Scaling refers to alter the size of the object or image (ie) a co-ordinate system is scaled by a factor.

40) What Do You Meant By Shrinking Of Digital Images?

Shrinking may be viewed as under sampling. If an image is been shrinked by one half, we delete every row and column. To reduce possible aliasing effect, it is a good idea to blue an image slightly before shrinking it.

41) Explain Subjective Brightness And Brightness Adaptation?

Subjective brightness means intensity as preserved by the human visual system . Brightness adaptation means the human visual system can operate only from scotopic to glare limit. It cannot operate over the range simultaneously. It performs large variation by changes in its overall intensity.

42) What Are The Steps Involved In Dip?

They are as follows.

– Image Acquisition

– Preprocessing

– Segmentation

– Representation and Description

43) How can we Increase the Quality of an Image?

– Recognition and Interpretation

Image enhancement process is purely dependent on the application where we need to use the enhanced image and the type of degradation in the image. Few solutions from my basic knowledge

– If image contain so much noises, apply filtering operations such as mean/median etc.

– If the image is looking too dark or too bright apply histogram equalization process to improve the contrast.

– If the image is blurred apply sharpening operations in the image.

44) What Is Image Transform?

An image can be expanded in terms of a discrete set of basis arrays called basis images. Hence, these basis images can be generated by unitary matrices. An NxN image can be viewed as an N^2×1 vectors. It provides a set of coordinates or basis vectors for vector space.

45) What Do You Meant By Zooming Of Digital Images?

Zooming may be viewed as over sampling. Zooming involves the creation of new pixel locations and the assignment of gray levels to those new locations.

46) What Is The Need For Transform?

The need for transform is most of the signals or images are time domain signal (ie) signals can be measured with a function of time. This representation is not always best. Any person of the mathematical transformations is applied to the signal or images to obtain further information from that signal. Particularly, for image processing.

47) List The Hardware Oriented Color Models?

They are as follows.

– RGB model

– CMY model

– YIQ model

– HSI model

48) What Is Chromatic Adoption?

The hue of a perceived color depends on the adoption of the viewer.

For example:

The Russian Flag will not immediately appear red, white, and blue of the viewer has been subjected to high intensity red light before viewing the flag. Thus the color of the flag will appear to shift in hue toward the red component cyan.

49) What Is Meant By Pixel?

A digital image is composed of a finite number of elements each of which has a particular location or value. These elements are referred to as pixels or image elements or picture elements or pixls elements.

50) What Is Geometric Transformation?

Transformation is used to alter the co-ordinate description of image.The basic geometric transformations are

– Image translation

– Scaling

– Image rotation

Rajesh Kumar
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