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MMSE Approximation for the Sparse Prior Using Stochastic Resonance Dror Simon Computer Science, Technion, Israel January 15, 2020 Joint work with Jeremias Sulam, Yaniv Romano, Yue M. Lu and Michael Elad Dror Simon (Technion) MMSE for Sparse


  1. MMSE Approximation for the Sparse Prior Using Stochastic Resonance Dror Simon Computer Science, Technion, Israel January 15, 2020 Joint work with Jeremias Sulam, Yaniv Romano, Yue M. Lu and Michael Elad Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 1 / 46

  2. Noise Removal Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 2 / 46

  3. Noise Removal Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 2 / 46

  4. Noise Removal Why denoising? Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 2 / 46

  5. Noise Removal Why denoising? A simple testing ground for novel concepts in signal processing. Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 2 / 46

  6. Noise Removal Why denoising? A simple testing ground for novel concepts in signal processing. Can be generalized to other, more complicated applications. Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 2 / 46

  7. Noise Removal Noisy Signal Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 3 / 46

  8. Noise Removal Noisy Signal Clean Estimate Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 3 / 46

  9. Noise Removal Noisy Signal Signal Clean Restoration Estimate Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 3 / 46

  10. Noise Removal Noisy Signal Signal Clean Restoration Estimate Prior Knowledge Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 3 / 46

  11. Noise Removal – Bayesian Standpoint Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 4 / 46

  12. Noise Removal – Bayesian Standpoint Denoising Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 4 / 46

  13. Noise Removal – Bayesian Standpoint Signal Estimation Denoising Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 4 / 46

  14. Noise Removal – Bayesian Standpoint Signal Approx. Estimation Denoising Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 4 / 46

  15. Noise Removal – Bayesian Standpoint Suboptimal Signal Approx. Estimation Denoising Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 4 / 46

  16. Noise Removal – Bayesian Standpoint Suboptimal Signal Approx. Estimation Denoising Optimal Signal Estimation Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 4 / 46

  17. Noise Removal – Bayesian Standpoint Suboptimal Signal Approx. Estimation Denoising Optimal Signal Approx. Estimation Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 4 / 46

  18. Outline Bayesian Framework 1 The Generative Model Bayesian Estimators MMSE Approximation 2 Previous Work Stochastic Resonance 3 Can Noise Help Denoising? Our Proposed Method 4 The Algorithm Unitary Case Analysis Image Denoising Conclusions 5 Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 5 / 46

  19. Outline Bayesian Framework 1 The Generative Model Bayesian Estimators MMSE Approximation 2 Previous Work Stochastic Resonance 3 Can Noise Help Denoising? Our Proposed Method 4 The Algorithm Unitary Case Analysis Image Denoising Conclusions 5 Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 6 / 46

  20. The Generative Model D ∈ R n × m is a dictionary with normalized columns. m n D Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 7 / 46

  21. The Generative Model Each element i in α is non zero with probability p i ≪ 1. m n D α Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 7 / 46

  22. The Generative Model The non-zero elements of the sparse representation, denoted by α s , are � � 0 , σ 2 sampled from a Gaussian distribution α s | s ∼ N . α I | s | m n D α Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 7 / 46

  23. The Generative Model The product D α leads to a signal x . m = n D x α Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 7 / 46

  24. The Generative Model We are given noisy measurements y = D α + ν , where ν is a white � � 0 , σ 2 Gaussian noise ν ∼ N . ν I n m = n D x α Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 7 / 46

  25. The Generative Model – Results 1 Turek, Javier S., Irad Yavneh, and Michael Elad, 2011. ”On MMSE and MAP denoising under sparse representation modeling over a unitary dictionary.” Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 8 / 46

  26. The Generative Model – Results The prior probability of a support (Bernoulli): p ( s ) = � � i ∈ s p i ∈ s (1 − p j ). j / 1 Turek, Javier S., Irad Yavneh, and Michael Elad, 2011. ”On MMSE and MAP denoising under sparse representation modeling over a unitary dictionary.” Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 8 / 46

  27. The Generative Model – Results The prior probability of a support (Bernoulli): p ( s ) = � � i ∈ s p i ∈ s (1 − p j ). j / When the support is known, y and α s are jointly Gaussian y = D s α s + ν , leading to 1 1 Turek, Javier S., Irad Yavneh, and Michael Elad, 2011. ”On MMSE and MAP denoising under sparse representation modeling over a unitary dictionary.” Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 8 / 46

  28. The Generative Model – Results The prior probability of a support (Bernoulli): p ( s ) = � � i ∈ s p i ∈ s (1 − p j ). j / When the support is known, y and α s are jointly Gaussian y = D s α s + ν , leading to 1 y | s is Gaussian: y | s ∼ N ( 0 , C s ). 1 Turek, Javier S., Irad Yavneh, and Michael Elad, 2011. ”On MMSE and MAP denoising under sparse representation modeling over a unitary dictionary.” Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 8 / 46

  29. The Generative Model – Results The prior probability of a support (Bernoulli): p ( s ) = � � i ∈ s p i ∈ s (1 − p j ). j / When the support is known, y and α s are jointly Gaussian y = D s α s + ν , leading to 1 y | s is Gaussian: y | s ∼ N ( 0 , C s ). � � D s α s , σ 2 y | α s , s is Gaussian: y | α s , s ∼ N ν I n . 1 Turek, Javier S., Irad Yavneh, and Michael Elad, 2011. ”On MMSE and MAP denoising under sparse representation modeling over a unitary dictionary.” Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 8 / 46

  30. The Generative Model – Results The prior probability of a support (Bernoulli): p ( s ) = � � i ∈ s p i ∈ s (1 − p j ). j / When the support is known, y and α s are jointly Gaussian y = D s α s + ν , leading to 1 y | s is Gaussian: y | s ∼ N ( 0 , C s ). � � D s α s , σ 2 y | α s , s is Gaussian: y | α s , s ∼ N ν I n . � � 1 ν Q − 1 s D T s y , Q − 1 α s | y , s is Gaussian: α s | y , s ∼ N . σ 2 s Q s = 1 I | s | + 1 C s = σ 2 α D s D T s + σ 2 D T ν I n , s D s σ 2 σ ν α 1 Turek, Javier S., Irad Yavneh, and Michael Elad, 2011. ”On MMSE and MAP denoising under sparse representation modeling over a unitary dictionary.” Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 8 / 46

  31. Outline Bayesian Framework 1 The Generative Model Bayesian Estimators MMSE Approximation 2 Previous Work Stochastic Resonance 3 Can Noise Help Denoising? Our Proposed Method 4 The Algorithm Unitary Case Analysis Image Denoising Conclusions 5 Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 9 / 46

  32. Bayesian Estimators The goal: Estimate α given the noisy measurements y , i.e. denoise the signal. Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 10 / 46

  33. Bayesian Estimators The goal: Estimate α given the noisy measurements y , i.e. denoise the signal. Many estimators can be proposed. We focus our attention on three: Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 10 / 46

  34. Bayesian Estimators The goal: Estimate α given the noisy measurements y , i.e. denoise the signal. Many estimators can be proposed. We focus our attention on three: 1 The oracle estimator. Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 10 / 46

  35. Bayesian Estimators The goal: Estimate α given the noisy measurements y , i.e. denoise the signal. Many estimators can be proposed. We focus our attention on three: 1 The oracle estimator. 2 The Maximum A-posteriori Probability (MAP) estimator. Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 10 / 46

  36. Bayesian Estimators The goal: Estimate α given the noisy measurements y , i.e. denoise the signal. Many estimators can be proposed. We focus our attention on three: 1 The oracle estimator. 2 The Maximum A-posteriori Probability (MAP) estimator. 3 The Minimum Mean Square Error (MMSE) estimator. Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 10 / 46

  37. The Bayesian Estimators Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 11 / 46

  38. The Bayesian Estimators Oracle Estimator = E { α s | s , y } = 1 α Oracle Q − 1 s D T � s y s σ 2 ν Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 11 / 46

  39. The Bayesian Estimators MAP Support Estimator � s MAP = arg max p ( s | y ) s Dror Simon (Technion) MMSE for Sparse Prior January 15, 2020 11 / 46

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