tell me how to find the coset leaders simply
To find the coset leaders simply, you can use the following steps:
Identify the subgroup: Start by identifying the subgroup for which you want to find the coset representatives.
Choose a set of representatives: Select a set of representatives for the cosets. These representatives should be the elements of the group that are not already in the subgroup. The number of representatives chosen should be equal to the index of the subgroup in the group.
Calculate the cosets: For each chosen representative, multiply it with every element of the subgroup. This will generate the different cosets.
Identify and remove duplicates: Identify and remove any duplicate elements from the cosets, leaving only one representative for each coset.
Verify the coset representatives: Check that the coset representatives obtained form a complete set of representatives for the cosets.
By following these steps, you can efficiently find the coset leaders simply.
• Nearest pixel – integer pixel, Higher accuracy is required for stabilization or stitching • Sub-pixel estimates – Evaluate several values (u,v) around the best value – Interpolate the matching score to find the analytic minimum SSD energy and Taylor series expansion Lucas and Kanade (1981) Image gradient or Jacobian at (x+u) Current intensity error (residual error) • For efficiency – Precompute the Hessian and Jacobian image: save significant computation – Precompute the inner product between the gradient field and shifted version of I1 allows the iterative re-computation of ei to be performed in constant time (independent of the number of pixels) Iterations – The effectiveness relies on the quality of Taylor series approximation – When far away from the true displacement (say, 1– 2 pixels), several iterations may be needed – It is possible to estimate a value for J_1 using a least squares fit to a series of larger displacements in order to increase the range of convergence (Jurie and Dhome 2002) or to “learn” a special-purpose recognizer for a given patch Stopping criterion – monitor the magnitude of the displacement correction |u| and to stop when it drops below a certain threshold (say, 1/10 of a pixel) For larger motions – combine the incremental update rule with a hierarchical coarse-to-fine search strategy. summarize the paragraph
The paragraph outlines a method for image stabilization and stitching using techniques such as nearest pixel and sub-pixel estimates, as well as strategies for efficiency and handling larger motions. It discusses the use of SSD energy and Taylor series expansion, interpolation of matching scores, computation of image gradients and Jacobians, precomputation of Hessian and Jacobian images, iterative computation of error in constant time, and the use of iterations and criteria for displacement correction. Additionally, it mentions a hierarchical coarse-to-fine search strategy for handling larger motions.
• Nearest pixel – integer pixel, Higher accuracy is required for stabilization or stitching • Sub-pixel estimates – Evaluate several values (u,v) around the best value – Interpolate the matching score to find the analytic minimum SSD energy and Taylor series expansion Lucas and Kanade (1981) Image gradient or Jacobian at (x+u) Current intensity error (residual error) • For efficiency – Precompute the Hessian and Jacobian image: save significant computation – Precompute the inner product between the gradient field and shifted version of I1 allows the iterative re-computation of ei to be performed in constant time (independent of the number of pixels) Iterations – The effectiveness relies on the quality of Taylor series approximation – When far away from the true displacement (say, 1– 2 pixels), several iterations may be needed – It is possible to estimate a value for J_1 using a least squares fit to a series of larger displacements in order to increase the range of convergence (Jurie and Dhome 2002) or to “learn” a special-purpose recognizer for a given patch Stopping criterion – monitor the magnitude of the displacement correction |u| and to stop when it drops below a certain threshold (say, 1/10 of a pixel) For larger motions – combine the incremental update rule with a hierarchical coarse-to-fine search strategy. explain the paragraph
The paragraph discusses various techniques and considerations for image stabilization and stitching processes.
Nearest pixel and sub-pixel estimates are mentioned as methods for achieving higher accuracy in stabilization or stitching by evaluating the nearest integer pixel as well as several sub-pixel values to interpolate the matching score.
The use of Sum of Squared Differences (SSD) energy and Taylor series expansion, as described in Lucas and Kanade's work from 1981, is recommended. This involves calculating image gradients or Jacobians at specific positions and using the current intensity error (residual error) to drive the optimization process.
To improve efficiency, precomputation of the Hessian and Jacobian image is suggested to save significant computation. This precomputation allows for the iterative re-computation of error to be performed in constant time, independent of the number of pixels.
The paragraph mentions the importance of iterations in the effectiveness of the Taylor series approximation, particularly when dealing with displacements of 1-2 pixels. It also discusses the possibility of estimating a for J_1 using a least squares fit to a series of larger displacements to increase the range of convergence or to "learn" a special-purpose recognizer for a given patch.
A stopping criterion is proposed, where the magnitude of the displacement correction (|u|) is monitored, and the process is stopped when it drops below a certain threshold (e.g., 1/10 of a pixel).
Finally, for larger motions, the suggestion is to combine the incremental update rule with a hierarchical coarse-to-fine search strategy.
Overall, the paragraph provides an overview of the various techniques and considerations involved in the process of image stabilization and stitching, encompassing both pixel-level and sub-pixel optimizations, efficiency enhancements, iterative approaches, and strategies for handling larger motions.
• Nearest pixel – integer pixel, Higher accuracy is required for stabilization or stitching • Sub-pixel estimates – Evaluate several values (u,v) around the best value – Interpolate the matching score to find the analytic minimum SSD energy and Taylor series expansion Lucas and Kanade (1981) Image gradient or Jacobian at (x+u) Current intensity error (residual error) • For efficiency – Precompute the Hessian and Jacobian image: save significant computation – Precompute the inner product between the gradient field and shifted version of I1 allows the iterative re-computation of ei to be performed in constant time (independent of the number of pixels) Iterations – The effectiveness relies on the quality of Taylor series approximation – When far away from the true displacement (say, 1– 2 pixels), several iterations may be needed – It is possible to estimate a value for J_1 using a least squares fit to a series of larger displacements in order to increase the range of convergence (Jurie and Dhome 2002) or to “learn” a special-purpose recognizer for a given patch Stopping criterion – monitor the magnitude of the displacement correction |u| and to stop when it drops below a certain threshold (say, 1/10 of a pixel) For larger motions – combine the incremental update rule with a hierarchical coarse-to-fine search strategy. explain the paragraph shortly
The paragraph outlines techniques for image stabilization and stitching. It discusses the use of nearest pixel and sub-pixel estimates, SSD energy, Taylor series expansion, image gradients, residual error computation, and precomputation of the Hessian and Jacobian for efficiency. Additionally, it covers the importance of iterations, stopping criteria, and handling larger motions using incremental update and coarse-to-fine search strategy. These methods aim to improve accuracy, computational efficiency, and convergence when stabilizing or stitching images.
Fourier-based alignment relies on the fact that the Fourier transform of a shifted signal has the same magnitude as the original signal but a linearly varying phase where ω is the vector-valued angular frequency of the Fourier transform and we use cal-ligraphic notation I1(ω) = F {I1(x)} to denote the Fourier transform of a signal • Another useful property of Fourier transforms is that convolution in the spatial domain corresponds to multiplication in the Fourier domain Fourier trans-form of the cross-correlation function ECC can be written as
is the correlation function, i.e., the convolution of one signal with the reverse of the other,and I∗1 (ω) is the complex conjugate of I1(ω) While Fourier-based convolution is often used to accelerate the computation of image correlations, it can also be used to accelerate the sum of squared differences function (and its variants) . Its Fourier transform can be written as SSD function can be computed by taking twice the correlation function and sub-tracting it from the sum of the energies in the two images. explain the paragraph
The paragraph presents the application of Fourier-based techniques for signal alignment and correlation computation in image processing:
Fourier Transform of Shifted Signal: It explains that the Fourier transform of a shifted signal has the same magnitude as the original signal but a linearly varying phase, denoted by I1(ω) = F {I1(x)}. Here, I1(ω) represents the Fourier transform of a signal, where ω is the vector-valued angular frequency.
Convolution Property: It highlights that convolution in the spatial domain corresponds to multiplication in the Fourier domain. The Fourier transform of the cross-correlation function ECC can be expressed as a product involving the Fourier domain representation of the signals and their complex conjugates.
Application to Sum of Squared Differences (SSD) Function: The passage states that Fourier-based convolution is commonly used to accelerate the computation of image correlations, including the sum of squared differences function and its variants. The Fourier transform of the SSD function is derived as an equation involving the correlation function, and it explains that the SSD function can be computed by manipulating the energies in the two images using the correlation function.
In essence, the paragraph emphasizes the utility of Fourier-based methods in efficiently computing signal alignment, correlation functions, and specific metrics like the sum of squared differences in the context of image processing.
If the object of interest is rotating around a fixed but unknown axis, specialized techniques can be used to recover this motion. • In other situation, the camera itself may be moving in a fixed arc around some center of rotation. • Specialized capture steps, such as mobile stereo camera rings or moving vehicles equipped with multiple fixed cameras, can also take advantage of the knowledge that individual cameras are mostly fixed with respect to the capture rig.
Line-based technique: Pairwise epipolar geometry cannot be recovered from line matches alone, even if the cameras are calibrated. • Consider projecting the set of lines in each image into a set of 3D planes in space. You can move the two cameras around into any configuration and still obtain a valid reconstruction for 3D lines. When lines are visible in three or more views, the trifocal tensor can be used to transfer lines from one pair of image to another. The trifocal tensor can also be computed on the basis line matches alone. • For triples of images, the trifocal tensor is used to verify that the lines are in geometric correspondence before evaluating the correlations between line segments. Plane-based technique: Better approach is to hallucinate virtual point correspondences within the area from which each homography was computed and to feed them into a standard structure from motion algorithm explain the paragraph
The paragraph delves into specialized techniques for recovering the motion of objects or cameras in different scenarios, specifically focusing on line-based and plane-based techniques in the context of camera motion and geometric correspondence:
Specialized Capture Scenarios: It mentions scenarios where specialized capture steps, such as using mobile stereo camera rigs or moving vehicles equipped with fixed cameras, can be leveraged to take advantage of the fixed nature of individual cameras relative to the capture rig.
Line-Based Technique: The passage explains that recovering pairwise epipolar geometry from line matches alone, even with calibrated cameras, is not. Instead, it suggests projecting the set of lines in each image into 3D planes in space, allowing for a valid reconstruction of 3D lines even with varying camera configurations. When lines are visible in three or more views, the trifocal tensor is utilized to transfer lines between image pairs, and it can be computed based on line matches alone. Additionally, the trifocal tensor is used to verify geometric correspondence of lines in triples of images before evaluating correlations between line segments.
Plane-Based Technique: The paragraph proposes a more effective approach of generating virtual point correspondences within the computed area of each homography and incorporating these into a standard structure-from-motion algorithm. This technique aims to enhance the reconstruction of3D scenes by leveraging plane-based methodologies.
Overall, the paragraph provides insights into leveraging specialized techniques such as line-based and plane-based approaches to recover the motion of objects and cameras in various capture scenarios, emphasizing the use of trifocal tensors and virtual point correspondences for improved geometric correspondence and reconstruction.
Structure from motion involves the estimation of so many highly coupled parameters, often with no known “ground truth” components. The estimates produces by structure from motion algorithm can often exhibit large amounts of uncertainty . ex: bas-relief ambiguity, which makes it hard to simultaneously estimate 3D depth of scene and the amount of camera motion. A unique coordinate frame and scale for areconstructed scene can not be recovered from monocular visual measurements alone. This seven-degrees-of-freedom gauge ambiguity makes it tricky to compute the variance matrix associated with a 3D reconstruction. To compute a convex matrix that ignores gauge freedom is to throw away the seven smallest eigenvalues of the information matrix, whose values are equivalent to the problem Hessian A up to noise scaling. explain the paragraph
The paragraph discusses several challenges and ambiguities inherent in the process of estimating parameters and reconstructing scenes using structure from motion algorithms:
Coupled Parameter Estimation: It acknowledges the difficulty of estimating numerous highly interconnected parameters within structure from motion, especially when there is no known "ground truth" or reference components available for comparison.
Uncertainty in Estimates: It highlights that the estimates produced by structure from motion algorithms often exhibit significant uncertainty. It gives the example of the "bas-relief ambiguity," which complicates the simultaneous estimation of the 3D depth of a scene and the extent of camera motion.
Unique Coordinate Frame and Scale Recovery: It emphasizes that reconstructing a unique coordinate frame and scale for a scene cannot be achieved solely from monocular visual measurements.
Gauge Ambiguity: It points out the presence of a seven-degrees-of-freedom gauge ambiguity, making it to compute the variance matrix associated with a 3D reconstruction. This ambiguity can introduce complexities in accurately characterizing the uncertainty in the reconstructed parameters.
Handling Ambiguity: The paragraph suggests a method to address the gauge freedom by computing a convex matrix that disregards the ambiguity. This involves discarding the seven smallest eigenvalues of the information matrix, aligning with the problem Hessian A (a matrix of second derivatives) up to scaling by noise.
In summary, the paragraph illuminates the complexities and uncertainties in structure from motion, especially related to parameter estimation, ambiguities in scene and camera motion reconstruction, and the challenges of addressing the gauge ambiguity to compute variance matrices for 3D reconstructions. Despite these challenges, the discussion hints at potential strategies for mitigating these issues.