CS 754 - Advanced Image Processing (aka Inverse Problems in Image Processing)



Course Information

Course Description

Besides being just two- or three-dimensional arrays containing numbers (pixel intensity values), the images that are seen and acquired in everyday life have a number of very interesting properties. For example, small patches from different spatial regions of an image are quite similar to each other. Another example is that these images when transformed by certain kinds of matrix operations (eg: wavelet or discrete cosine transform) produce coefficients that are very sparse (i.e. most of them are zero or close to zero in value). These properties are a key to developing efficient and accurate algorithms for a variety of applications such as image noise removal, blur removal, image separation, compression and even image-based forensics. Not just that, these properties have also inspired the design of new sensors to acquire images much faster (a technology called compressed sensing) which is really crucial in tasks involving video or some types of images in medicine (such as magnetic resonance imaging - MRI). This course will systematically study several such techniques motivated by these interesting properties of natural images. The course will explore some key theory (including the proofs of some truly beautiful theorems), algorithms, as well as many applications. It will expose students to a broad range of modern, state-of-the-art techniques in image processing. A more detailed (tentative) syllabus can be accessed here. Many of the problems we will deal with in this class fall in the category of inverse problems, i.e. problems where the number of unknowns seems to exceed the number of knowns, at superficial glance, and there is also noise or system matrix contamination.

Many of the techniques studied in this course are very relevant in the era of BIG DATA, and they focus on intelligent acquisition of data. Can we acquire data in a compressed format so as to save resources: time, radiation given to a patient in a CT scanner, electrical power? Surprisingly, though we study these techniques in the context of image processing, the techniques are very generic and applicable in a variety of other domains. Last year at the beginning of the pandemic, many students in this course helped me and a colleague in developing techniques for saving resources used in COVID-19 RTPCR testing!

Need for the course Image Processing Applications

The course will cover principled techniques that can be applied to some interesting image processing problems:

Intended Audience and Pre-requisites

Intended for UG students from the second year onward, DDP students, and all PG students (MTech/PhD) from CSE/EE/EP/CSRE/Earth Sciences. You must have taken CS 663 or EE 610 or CS 725, otherwise you must discuss with me whether you have suitable background for this course.

Textbooks

Resources


Grading scheme (tentative)

Webpages of Previous Offerings


Course project

Project Topics and Instructions

Detailed Schedule

Date

Content of the Lecture

Assignments/Readings/Notes

Lecture 1: 5/1 (Fri)
  • Course overview
  • Intro to compressed sensing, tomography, dictionary learning, low rank matrix recovery
Lecture 2: 9/1 (Tue)
  • Compressed sensing (CS): introduction and motivation
  • Review of DFT and DCT, Review of JPEG, representation of a signal/image as a linear combination of basis vectors
  • Sparsity of natural images in transform bases
  • Candes, Romberg, Tao: puzzling experiment; Basic optimization problem for CS involving the total variation (i.e. sum total gradient magnitude of the image)
Lecture 3: 12/1 (Fri)
  • Concept of incoherence between sensing matrix and representation basis
  • Theorem 1 for reconstruction guarantees
  • Whittaker-Shannon sampling theorem
  • Comparison between Theorem 1 and Shannon's sampling theorem.
  • Further comments on theorem 1
  • Intuition behind incoherence
Lecture 4: 16/1 (Tue)
  • Concept of restricted isometry property (RIP)
  • Theorems 2 and 3 and comments on them
  • Motivation for use of L1 norm instead of L2 norm for compressed sensing
Lecture 5: 19/1 (Fri)
  • Toy sample experiments in compressed sensing
  • CS for piecewise constant signals: Theorem 4
  • Concept of mutual coherence, and its comparison to RIC
  • Theorem 5, similar to theorem 3, but using mutual coherence
Lecture 6: 23/1 (Tue)
  • RIC and singular values of the sensing matrix
  • Bandlimited signal reconstruction under impulse noise
  • Algorithms for compressed sensing: matching pursuit (MP) and orthogonal matching pursuit (OMP)
Lecture 7: 30/1 (Tue)
  • Algorithms for compressed sensing: iterated shrinkage and thresholding algorithm (ISTA)
  • Rice single pixel camera, and its block-based version
Lecture 8: 2/2 (Fri)
  • Rice single pixel camera in video mode: separate frame-by-frame reconstruction, coupled reconstruction
  • CASSI camera for compressive hyperspectral imaging
Lecture 9: 6/2 (Tue)
  • CASSI camera for compressive hyperspectral imaging: details of forward models
  • Color filter arrays and color image demosaicing
Lecture 10: 9/2 (Fri)
  • CASSI camera for compressive hyperspectral imaging: details of forward models
  • Color filter arrays and color image demosaicing
  • RTPCR noise model
  • Concept of tradeoff between spatial and temporal resolution in image acquisition
  • Video snapshot compressive sensing: concept, hardware description, results
  • CS in MRI
Lecture 11: 13/2 (Tue)
  • CS in MRI
  • Sketch of the proof of theorem 3; review of various inequalities involving vectors
  • Compressed sensing matrix design
  • Compressive classification
Lecture 12: 16/2 (Fri)
  • Compressive classification

Tomography
  • Introduction to tomography
  • Radon transforms
  • Backprojection
Lecture 13: 20/2 (Tue)
  • Radon transforms, Fourier slice theorem
  • Backprojection and filtered backprojection
  • CS for tomography; concept of function handles
Lecture 14: 5/3 (Tue)
  • CS for tomography; concept of function handles; couple CS for reconstruction of consecutive tomographic slices
  • Cryo-electron microscopy: introduction, concept of micrograph/particle
  • Tomography under unknown angles (2D images, 1D projections): Helgason Ludwig consistency conditions (HLCC), inherent ambiguity in tomography under unknown angles
  • Theoretical results in tomography under unknown angles (stated without proof)
  • Algorithms for tomography under unknown angles: moment-based method, algorithm by Basu and Bresler based on ordering
Lecture 15: 8/3 (Fri)
  • Algorithms for tomography under unknown angles: moment-based method, algorithm by Basu and Bresler based on ordering
  • algorithm based on dimensionality reduction using Laplacian eigenmaps
  • Correction for unknown shifts in tomography under unknown angles; usage of order statistics for ordering and dimensionality reduction methods
  • Tomography under unknown angles in 3D: concept of common line, algorithms for determining common lines
  • Algorithm for finding unknown angles and underlying 3D structure from 2D projections under unknown angles - case of 3 projections only
  • Algorithm or finding unknown angles (based on semi-definite programming) and underlying 3D structure from 2D projections under unknown angles - case of N projections
Lecture 16: 12/3 (Fri)
  • Algorithm or finding unknown angles (based on semi-definite programming) and underlying 3D structure from 2D projections under unknown angles - case of N projections
  • Cryo-EM complete pipeline, concept of cryo-electron tomography and its difference from single particle cryo-EM
  • Orthogonal procrustes algorithm
Lecture 17: 16/3 (Tue) Low rank matrix recovery
  • Low rank matrices in data scienc, computer vision and image processing
  • Concept and key theorem + estimator for low rank matrix completion; inherent limitations of low rank matrix completion and concept of matrix coherence
  • Experimental results for low rank matrix completion
Lecture 18: 26/3 (Tue)
  • Singular value thresholding for low rank matrix completion, with some properties and numerical results
  • Concept of compressive low rank matrix recovery, related theorems and applications
Lecture 19: 2/4 (Tue)
  • Robust principal components analysis: application scenarios
  • Key theorems for RPCA; some experimental results
  • Alternationg Lagrangian Method (ALM) for RPCA
Lecture 20: 5/4 (Fri)
  • Compressive RPCA: concept and key theorem
  • SparCS algorithm for compressive RPCA; CoSamp algorithm for compressed sensing
  • Experimental results for compressive RPCA for compressive hyperspectral image reconstruction and compressive video recovery
Dictionary Learning
  • Concept of dictionary learning and dictionary coefficients
  • Orthonormal and overcomplete dictionaries; overcompleteness and sparsity; sparse coding for orthonormal and overcomplete dictionaries
  • KMeans as a special case of dictionary learning
Lecture 21: 12/4 (Fri)
  • Dictionary learning using Olshausen's method, Method of optimal directions
  • KSVD method for dictionary learning, with applications to lossy image compression
Lecture 22: 16/4 (Tue)
  • Non-negative matrix factorization (NMF), non-negative sparse coding (NNSC)
  • Bayesian statistics: basics, applications in image denoising and deblurring; concept of MAP, posterior probabilities with gaussian likelihood and Lapalcian and Gaussian priors
  • Statistical compressed sensing using Gaussian distributions and Gaussian Mixture Models
Lecture 23: 16/4 (Tue)
  • KSVD for denoising and inpainting; KSVD for video compressive sensing for snapshot-coded images;
  • Blind compressive sensing
  • Compressed sensing with overcomplete dictionaries
  • Dictionary learning via unions of orthonormal bases