Computer Vision Lecture 7: Features III Object Recognition Quiz

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Questions and Answers

What is the purpose of using Bag of Words (BOW) in image recognition?

  • To convert the image into a text document
  • To analyze the language used in the image
  • To represent an image using a histogram of visual word occurrences (correct)
  • To count the number of words in the image

In feature-based alignment, what is the purpose of computing and applying the best transformation such as affine, translation, or rotation?

  • To change the color space of the images
  • To align and match features between two images (correct)
  • To add extra details to the images
  • To compress the images for better storage

What technique is used to address getting a set of incorrect matches (outliers) in feature-based alignment?

  • Principal Component Analysis (PCA)
  • Random Sample Consensus (RANSAC) (correct)
  • Nearest Neighbor Search
  • K-means Clustering

Why is it important to loop until happy in feature-based alignment?

<p>To continuously improve the matching and alignment results (B)</p> Signup and view all the answers

What is the main task when using Harris, SIFT, etc. in building panoramas?

<p>Detecting and describing features in both images (B)</p> Signup and view all the answers

What role does scientific computing play in object recognition and image processing?

<p>It provides computational methods for analyzing and processing images (A)</p> Signup and view all the answers

What is the purpose of the RANSAC algorithm?

<p>To iteratively refine a model by selecting the best subset of inliers (B)</p> Signup and view all the answers

What does the 'N' represent in RANSAC?

<p>Number of iterations to find the best model (A)</p> Signup and view all the answers

How is the initial number of points 's' chosen in RANSAC?

<p>It is typically the minimum number needed to fit the model (C)</p> Signup and view all the answers

What is the role of the distance threshold 'T' in RANSAC?

<p>To select points within error bounds of the model (C)</p> Signup and view all the answers

What does RANSAC do after obtaining a consensus set of inliers?

<p>It terminates and returns the model (B)</p> Signup and view all the answers

What is the adaptive procedure in RANSAC used for?

<p>To dynamically adjust parameters during model fitting (C)</p> Signup and view all the answers

What does 'e' represent in the adaptive procedure of RANSAC?

<p>Error bound for selecting points within a consensus set (B)</p> Signup and view all the answers

How is the distance threshold 'T' chosen in RANSAC?

<p>'T' is chosen to ensure a high probability for inliers (C)</p> Signup and view all the answers

What does 's' represent in RANSAC?

<p>Initial number of points needed to fit the model (C)</p> Signup and view all the answers

What is the main purpose of repeating steps 1-3 in RANSAC?

<p>To ensure that the best model is found with high confidence (C)</p> Signup and view all the answers

What was one of Lowe's goals in developing SIFT?

<p>To create an interest operator invariant to scale and rotation (A)</p> Signup and view all the answers

Which step in the SIFT algorithm involves eliminating edges and low contrast regions?

<p>Step 4: Eliminate edges and low contrast regions (A)</p> Signup and view all the answers

What is the main purpose of step 6 in the SIFT algorithm?

<p>Keypoint description (D)</p> Signup and view all the answers

What is the adaptive procedure used for in RANSAC?

<p>Choosing the number of points 's' (C)</p> Signup and view all the answers

In feature-based alignment, what does 'T' represent in RANSAC?

<p>The distance threshold (C)</p> Signup and view all the answers

What role does scientific computing play in object recognition and image processing?

<p>It enables efficient computation for feature extraction and matching (B)</p> Signup and view all the answers

What is the purpose of Step 3 in the SIFT algorithm?

<p>To eliminate edges and low contrast regions (B)</p> Signup and view all the answers

What is the difference between Laplacian of Gaussian (LoG) and Difference of Gaussian (DoG) in the SIFT algorithm?

<p>LoG is computationally expensive, while DoG is fast and efficient (D)</p> Signup and view all the answers

What is the main purpose of Step 4 in the SIFT algorithm?

<p>To eliminate edges and low contrast regions (D)</p> Signup and view all the answers

What is the role of orientation assignment in the SIFT algorithm?

<p>To assign orientation to keypoints (A)</p> Signup and view all the answers

How does Step 5 in the SIFT algorithm contribute to making keypoints invariant to variations such as changes in viewpoint and illumination?

<p>By rotating the window to standard orientation (D)</p> Signup and view all the answers

What is the purpose of creating a histogram of local gradient directions at selected scale in Step 5 of the SIFT algorithm?

<p>To assign orientation to keypoints (D)</p> Signup and view all the answers

How does Step 6 in the SIFT algorithm contribute to making keypoints invariant to changes in viewpoint and illumination?

<p>By normalizing the rotation and scale (C)</p> Signup and view all the answers

What is the reason behind breaking the 16x16 window into sixteen 4x4 windows in Step 6 of the SIFT algorithm?

<p>To compute a descriptor for the local image region (B)</p> Signup and view all the answers

What is the main purpose of rejecting points with bad contrast in Step 4 of the SIFT algorithm?

<p>To generate keypoints with sufficient contrast and distinctiveness (B)</p> Signup and view all the answers

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