Optical Flow Estimation: Lucas-Kanade Method

Optical Flow Estimation

• Represents the displacement of pixels between consecutive frames caused by object or camera movement
• Aims to compute the velocity field that describes this motion
• Lucas-Kanade method:
  • Assumes locally constant motion within a small neighborhood of pixels
  • Analyzes spatial gradients of intensity and temporal changes between frames
  • Formulates a system of linear equations to estimate motion vectors for each pixel or small region
• Horn-Schunck method:
  • Models optical flow as a smooth vector field that satisfies the brightness constancy constraint
  • Formulates a global energy minimization problem to compute the optical flow field
  • Imposes constraints such as smoothness and consistency between neighboring pixels

Interpolation

• Process of generating intermediate frames between existing frames in a video sequence
• Increases temporal resolution of the video or creates smooth motion effects
• Smaller block size produces a higher quality result, while larger block size results in a quicker scanning method but may compromise quality

Global Motion Estimation

• Technique used in computer vision to analyze and track large-scale motion in video sequences
• Identifies and estimates transformation parameters that describe the motion of objects or the camera across multiple frames
• Enables video stabilization, object tracking, and activity recognition

Uses of Motion Estimation

• Object tracking systems:
  • Enable real-time monitoring and tracing of objects or subjects within a specified area
  • Used in applications such as surveillance, sports analysis, and augmented reality
• Virtual and augmented reality:
  • Tracks user's movements and aligns virtual objects with the real-world environment
• Other applications:
  • Video compression, computer vision, and robotic navigation

Motion Estimation and Representation

• Involves analyzing consecutive frames of video to determine the motion of objects within the frames
• Accurate motion estimation is crucial for tasks like video encoding, object tracking, and autonomous navigation
• Motion representation refers to the visual depiction or description of movement in a graphical or symbolic form

Block-Based Motion Estimation

• Technique used in video compression to reduce redundancy by comparing blocks of pixels between frames
• Divides consecutive frames into blocks, then analyzes these blocks to determine the motion vectors
• Estimates motion at the block level, allowing for more efficient video compression
• Block size varies from 4x4 pixels to 32x32 pixels of scanning field, depending on screen size and resolution