Computer Vision Overview

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Questions and Answers

What is the main objective of computer vision as described in the content?

  • To develop new visual art techniques
  • To replace human vision
  • To recover three-dimensional shape and appearance of objects in imagery (correct)
  • To create optical illusions

Computer vision has fully solved the challenge of explaining an image at the level of a two-year-old.

False (B)

What are some of the methods used in computer vision to overcome the challenges of modeling the visual world?

Physics-based models, probabilistic models, and machine learning.

Researchers in computer vision can create accurate dense 3D surface models using __________ matching.

<p>stereo</p> Signup and view all the answers

Why is vision considered an 'inverse problem'?

<p>We seek to recover unknowns with insufficient information. (C)</p> Signup and view all the answers

Match the following techniques with their descriptions:

<p>Stereo matching = Creating dense 3D surface models Machine learning = Disambiguating potential solutions using examples Physics-based models = Modeling physical properties of light and objects Optical illusions = Demonstrating principles of human visual perception</p> Signup and view all the answers

What is the significance of using a large set of views of a particular object in computer vision?

<p>It allows for the creation of accurate dense 3D surface models.</p> Signup and view all the answers

Progress in computer vision has been stagnant over the past two decades.

<p>False (B)</p> Signup and view all the answers

What is the primary field that develops forward models used in computer vision?

<p>Physics and Computer Graphics (A)</p> Signup and view all the answers

The Müller-Lyer illusion involves two lines that appear to be of different lengths due to perspective effects.

<p>True (A)</p> Signup and view all the answers

What visual perception phenomenon explains why a white square in shadow appears different in brightness compared to a black square in light?

<p>Brightness constancy</p> Signup and view all the answers

The field of ___ focuses on how light reflects off surfaces and is scattered by the atmosphere in the context of computer vision.

<p>optics</p> Signup and view all the answers

Match the following optical illusions with their descriptions:

<p>Müller-Lyer illusion = Length perception influenced by perspective Brightness Constancy = Perception of brightness regardless of lighting Shadow Illusion = Same intensity perceived differently due to shadow Visual System = Processes and interprets visual information</p> Signup and view all the answers

In what aspect of computer vision are physics models most commonly applied?

<p>Object movement and animation (D)</p> Signup and view all the answers

Light only reflects off the surfaces of objects in an idealized manner, with no scattering effects.

<p>False (B)</p> Signup and view all the answers

How do models in computer graphics contribute to computer vision?

<p>They simulate object movement and light interactions.</p> Signup and view all the answers

What is the purpose of exposure bracketing in photography?

<p>To merge multiple exposures into a single image with optimal lighting (B)</p> Signup and view all the answers

Morphing involves transforming a photograph of an object into a 3D model.

<p>False (B)</p> Signup and view all the answers

What technique is used to navigate through a collection of photographs in 3D?

<p>Photo-based walkthroughs</p> Signup and view all the answers

_______ is a technique that merges overlapping photos into a single panorama.

<p>Stitching</p> Signup and view all the answers

Match the following computer vision applications with their descriptions:

<p>Stitching = Creating a panoramic image Face detection = Improving camera focusing Video match move = Inserting images into videos Visual authentication = Logging in users via webcam</p> Signup and view all the answers

Which technique allows for the removal of shake from videos?

<p>Video match move and stabilization (B)</p> Signup and view all the answers

Visual authentication can automatically log users onto their home computer.

<p>True (A)</p> Signup and view all the answers

What is one major reason for the focus on applications in computer vision?

<p>To motivate and inspire students by providing relevant problems.</p> Signup and view all the answers

What was a significant development in the 2000s regarding image-based rendering?

<p>Development of computational photography (C)</p> Signup and view all the answers

High dynamic range (HDR) images do not require tone mapping algorithms to be displayed.

<p>False (B)</p> Signup and view all the answers

What technique involves merging multiple exposures to create HDR images?

<p>Exposure bracketing</p> Signup and view all the answers

Image stitching and light-field capture are examples of __________ techniques.

<p>image-based rendering</p> Signup and view all the answers

Match the following techniques with their applications:

<p>Tone mapping = Displayable results from HDR images Inpainting = Restoring parts of an image Texture synthesis = Creating new textures from existing samples Image stitching = Combining multiple images into one</p> Signup and view all the answers

Which of these techniques is categorized under computational photography?

<p>Quilting (A)</p> Signup and view all the answers

Feature-based techniques combined with learning were mainly introduced in the 1990s.

<p>False (B)</p> Signup and view all the answers

Name one notable paper regarding object recognition from the 2000s.

<p>The constellation model or pictorial structures</p> Signup and view all the answers

What does the JPEG standard use for still images?

<p>An eight-bit range with no reserved values (A)</p> Signup and view all the answers

The HSV color space includes hue, saturation, and luminance.

<p>False (B)</p> Signup and view all the answers

What does saturation represent in the HSV color space?

<p>Scaled distance from the diagonal</p> Signup and view all the answers

The RGB color values obtained from a JPEG image are called __________.

<p>gamma-compressed</p> Signup and view all the answers

Match the following components with their definitions in the HSV color space:

<p>Hue = Direction around a color wheel Saturation = Scaled distance from the diagonal Value = Mean or maximum color value</p> Signup and view all the answers

Which formula is not essential for general use in image processing?

<p>Y0 matrix from the JPEG standard (B)</p> Signup and view all the answers

The Y xy coordinates are used to affect both saturation and hue in images.

<p>False (B)</p> Signup and view all the answers

What is the primary use of deblocking in image processing?

<p>To improve image quality</p> Signup and view all the answers

Which of the following image compression standards uses 8 × 8 DCT transforms?

<p>JPEG (C)</p> Signup and view all the answers

The DC coefficients in video compression are directly derived from the AC coefficients.

<p>False (B)</p> Signup and view all the answers

What is the main variable controlled by the quality setting on a JPEG file?

<p>step size in quantization</p> Signup and view all the answers

The alternative transformations used in JPEG 2000 are based on __________.

<p>wavelets</p> Signup and view all the answers

Match the compression standards with their corresponding block sizes:

<p>JPEG = 8 × 8 MPEG = 16 × 16 JPEG 2000 = Variable size AV1 = 4 × 4 or 2 × 2</p> Signup and view all the answers

Which compression standard is noted for using smaller block sizes like 4 × 4 or 2 × 2?

<p>AV1 (B)</p> Signup and view all the answers

Block-based motion compensation encodes the difference between each block and predicted pixel values from the current frame.

<p>False (B)</p> Signup and view all the answers

What type of coding scheme can be used to encode the coefficient values after transform coding?

<p>Huffman code or arithmetic code</p> Signup and view all the answers

Flashcards

What is computer vision?

Computer vision aims to enable computers to 'see' and interpret images and videos in the same way humans do, understanding objects, scenes, and actions.

3D Reconstruction in Computer Vision

The process of recovering the 3D shape and appearance of objects from images or videos. This is a challenging task due to the complex nature of the visual world.

Stereo Matching

Finding corresponding points between two images of the same scene, taken from slightly different viewpoints. This is crucial for reconstructing 3D models.

Machine Learning in Computer Vision

Computer vision models that learn from large datasets of images and labels, allowing them to identify patterns and make predictions. This is a powerful technique for tasks like object recognition, image classification, and scene understanding.

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Inverse Problem in Computer Vision

A problem where we try to find a solution based on limited information. In vision, we try to understand the world from the incomplete information in an image.

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Physics-based Modeling in Computer Vision

Techniques based on physics and probability to make sense of the visual world, helping computers understand the relationships between objects and their properties.

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Challenges of Computer Vision

Despite advances in computer vision, accurately understanding an image at the level of a young child remains a challenge. This is due to the complexity of the visual world and the limitations of current techniques.

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Complexity of the Human Visual System

The human visual system is incredibly complex and still not fully understood. This complexity makes it difficult to replicate human vision using computers.

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Forward Models in Computer Vision

The process of modeling how objects appear in images, taking into account factors like light, motion, and camera properties.

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Radiometry, Optics, and Sensor Design

Branches of physics that study how light interacts with objects and the principles of image formation.

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Relationship between Computer Graphics and CV Forward Models

Computer Graphics and Forward Models in Computer Vision are interconnected, both aim to create realistic images by simulating how light interacts with objects and environments.

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Brightness Constancy

The phenomenon where the visual system corrects for variations in illumination when interpreting the color of objects.

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Müller-Lyer Illusion

A visual illusion that demonstrates the visual system's sensitivity to perceived perspective and depth cues.

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Chessboard Illusion

A visual illusion illustrating how the visual system interprets the brightness of an object relative to its surroundings.

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Visual System Interpretation

The ability of the visual system to perceive and interpret light, color, and depth cues to understand the world around us.

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Object Motion and Animation

The way objects move, change shape, and interact with each other in a scene.

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Photo Stitching

Combining multiple overlapping photos to create a seamless panoramic image.

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Exposure Bracketing

Merging multiple photos taken with different exposures to create a perfectly exposed image.

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Morphing

Transforming one image into another through a smooth transition. This is often used to create dynamic effects.

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3D Modeling

Creating a 3D model of an object or person from one or more photos.

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Video Match Move and Stabilization

The process of tracking points in a video to insert 2D images or 3D models. Also used to stabilize shaky footage.

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Photo-based Walkthrough

Navigating through a collection of photos, often representing a space like a house, by flying between them in a 3D environment.

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Face Detection

A computer vision technique that identifies faces within an image.

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Visual Authentication

Using images for automatic authentication, often by recognizing faces for access control.

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Image-Based Modeling

The process of using images to create realistic 3D models, commonly used in fields like computer graphics and animation.

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Image Stitching

A technique for automatically stitching multiple images together to create a larger, panoramic view.

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Computational Photography

The field of computer vision that focuses on using computer vision techniques to enhance or manipulate images, often with the goal of producing improved or creative results.

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High Dynamic Range (HDR) Image Capture

Techniques used to capture and process images with a wide range of brightness values, allowing for details in both bright and dark areas.

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Tone Mapping

Algorithms that convert images with a wide dynamic range (HDR) to a displayable range, making them visible on monitors or prints.

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Feature-Based Object Recognition

A computer vision technique that analyzes images to recognize objects based on their distinctive features and shapes.

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Constellation Model

A model for object recognition that focuses on identifying constellations of distinctive features within an image.

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Pictorial Structures

A model for object recognition that represents objects as a set of interconnected parts or features, allowing for more complex descriptions.

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YCbCr Color Space

A color space represented by three components: Y (luminance), Cb (blue chroma difference), and Cr (red chroma difference). It's often used in image compression standards like JPEG.

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Gamma Compression in JPEG

The RGB color values obtained from a JPEG image are actually gamma-compressed. This means they are not the raw values, but rather a non-linear representation.

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HSV Color Space

A color space where colors are represented by their hue, saturation, and value. It's useful for tasks like color picking or manipulating an image's overall color appearance.

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Chroma Subsampling

A technique used in image compression to reduce the amount of data needed to store an image. It involves removing redundant information and representing color differences more efficiently.

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Image Blocking

A type of image artifact that can appear during image compression, particularly in JPEGs, where sharp edges or block boundaries become visible.

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Color Ratios (r, g, b)

A color space where colors are represented as normalized ratios of red, green, and blue components. It simplifies color manipulation by focusing on relative color proportions.

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Decompression for Gamma Correction

The process of restoring the original color information in an image by adjusting for gamma compression. This can be important when working with images that have been compressed using JPEG.

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Image Deblocking

A technique that involves analyzing and potentially correcting image artifacts that arise from compression, especially blockiness in images.

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JPEG Compression: DCT Transform

A method in image compression where the image is broken down into 8x8 blocks, transformed using Discrete Cosine Transform (DCT), and coefficients are quantized for efficient storage.

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JPEG Quality Setting

A measure of the amount of detail preserved in a compressed image. Higher quality settings result in more detail, larger file size.

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MPEG: Motion Compensation

A technique used in video compression to predict the motion of objects in a sequence of frames. It only encodes the changes between frames, saving space.

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MPEG (Moving Picture Experts Group)

A standard for compressing video and audio, widely used in streaming services and DVDs. Combines DCT transform, motion compensation, and other techniques for efficient encoding.

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DC Coefficient Prediction

A technique used in data compression, like JPEG, where the lowest frequency coefficient is used to predict the values of other coefficients, reducing redundancy.

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JPEG 2000 and JPEG XR

JPEG 2000 and JPEG XR use advanced techniques such as wavelets and lapped transforms to improve compression efficiency compared to traditional JPEG.

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Motion-JPEG (MJPEG)

A standard for video compression using only individual JPEG compressed frames, without motion compensation, resulting in larger file sizes.

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AV1 (AOMedia Video 1)

A new open standard for video compression that uses smaller blocks (4x4 or 2x2) and advanced techniques for better quality and efficiency.

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Study Notes

Computer Vision Module 1

  • Computer vision is about recreating the three-dimensional structure of the world from images.
  • Humans perceive 3D easily, but computers find it difficult.
  • Computer vision techniques use mathematical models and machine learning to infer properties from images (e.g., shape and appearance.)
  • Using large sets of partially overlapping photographs, 3D models can be created.
  • These advances are used in applications like optical character recognition, mechanical inspection, retail, warehousing logistics, and medical imaging.
  • Self-driving cars and drone-based photogrammetry are also enabled by computer vision.
  • Computer vision is an inverse problem; finding the solution is difficult.

Optical Illusions and Visual Perception

  • Illusions are used to test visual principles such as brightness constancy.
  • The visual system attempts to compensate for changes in lighting.
  • Visual perception is complex.
  • There is no easy solution to understanding the principles of visual perception.

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