Noise-Blind Image Deblurring Supplementary Material

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1 Noise-Blind Image Deblurring Supplementary Material Meiguang Jin University of Bern Switzerland Stefan Roth TU Darmstadt Germany Paolo Favaro University of Bern Switzerland A. Upper and Lower Bounds Our approach proposes a Bayesian generalization to Maimum a-posteriori (MAP). It is interesting to understand what relationship eists between MAP, the proposed epected loss, and the loss lower bound. It turns out that the logarithm of Bayes utility (BU) is bounded from below by our proposed bound and from above by the log of the MAP problem. We have log ma p(y ˆ; σ n)p(ˆ) = log ma p(ˆ, y; σ n) (MAP) ˆ ˆ = ma log ma p(ˆ, y; σ n) G(, ) d ˆ ma ma log p(, y; σ n )G(, ) d G(, ) log p(, y; σ n ) d. (BU) (lower bound) The second equation is due to the definition of G (it integrates to over ). Notice that as σ 0, the lower bound tends towards the MAP and thus they both converge to the logarithm of BU. B. A General Family of Image Priors We here show the applicability of our framework to a general family of image priors whose negative log-likelihood can be written as a concave function φ of terms F ik µ. As in the main paper, F i is a linear filter or a Toeplitz matri, e.g., F i =. Again as before, F ik yields the k th entry of the output and is therefore a row vector; µ and σ are parameters. Consequently, we have log p( ) = φ (ξ,..., ξ IJK ) with ξ ik = F ik µ. (39) Table 5 summarizes a few choices of φ for some popular image priors. Also notice that the type- Gumbel prior falls into this family as φ (ξ 0, ξ,..., ξ IJK ) = ξ 0 ik w i e ξ ik with ξ 0 = σ0, ξ ik = F ik µ σ (40) is a concave function ointly in all its arguments. These priors can have simple surrogate functions that yield simple Maorization Minimization (MM) 0 iterations. The concavity of φ gives the following inequality and surrogate function ψ( τ ) log p( ) log p( τ ) ik ( F ik µ ) F ik τ µ σ. = ψ( τ ). (4)

2 Image prior log p( ) φ( ( ) ) φ ( ( ) ) Gaussian σ, φ(w) = σ w(z) dz φ (w) = σ Total Variation σ, φ(w) = σ (w(z) + ɛ) dz φ (w) = 4σ (w(z) + ɛ) Sparsity (p < ) σ,p φ(w) = σ ( (w(z) + ɛ) p dz) p φ (w) = ( (w(z) + ɛ) p dz) p (w(z)+ɛ) p 4σ Table 5. Eamples of image priors, their negative log probability density functions, the corresponding φ functions, and derivative φ. The small coefficient ɛ > 0 is to avoid division by zero. Then, this yields the inequality G(, ) log p( ) d = = ik G(, )ψ( τ ) d G(, ) ik where all the constant terms do not depend on. C. Noise-Adaptive Deblurring F ik µ d + const (4a) (4b) F ik µ + const, (4c) The noise-adaptive algorithm in the general image prior family is analogous to that in the main paper for the Gumbel prior. We need to put all the terms together and solve the maimization of the lower bound arg ma G(, ) log p(, y; σ n ) d. (43),σ n Thus, we obtain the following iterative algorithm ( τ+ y k + Mσ k, ˆσ n ) = arg min,σ n σn + N log σ n + ik F ik µ. We can now solve eplicitly for ˆσ n and, as in the main paper, obtain ˆσ n = N y k + Mσ k. (45) This closed form can be incorporated in an iterative algorithm and yields τ+ N = arg min log y k + Mσ k + ik In the noise-blind deblurring formulation we can eplicitly obtain the gradient descent iteration τ+ = τ α λ τ K (K τ y) + F F ik τ µ ik σ ik σ (44) F ik µ. (46). (47) for some small step α > 0, where τ is the solution at gradient descent iteration τ and, as in the main paper, the noise adaptivity is given as λ τ = N y K τ +Mσ k.

3 TV-L Noise-Adaptive Deblurring. descent iteration τ+ = τ α Following from Eq. (47) the case of TV-L is then readily obtained as the gradient λ τ K (K τ y) + ( τ 4σ τ, ) (48) for some small step α > 0, where denotes the finite difference operator along the two coordinate aes, and τ and λ τ are defined as before. EPLL Noise-Adaptive Deblurring. noise-adaptive term λ τ = N y K τ +Mσ k In the case of EPLL 37, we modify the original Eq. (4) in 37 by introducing our and obtain τ+ = λ τ A A + β P P λ τ A y + β P z τ. (49) D. Back-Propagation in the GradNet Architecture In the following section we derive the gradients of GradNet with respect to its parameters. We first introduce the notation for the basic components of one stage in GradNet and then compute the gradients of this stage with respect to the parameters. The derivatives for the other stages will be similar. Initialization. To obtain 0 q at the stage τ = 0 we first pad the noisy blurry input using the constant boundary assumption (i.e., zero derivative at the boundary). Then we apply 3 iterations of MATLAB s edgetaper function to the padded noisy blurry input. We find eperimentally that this makes the reconstructed image converge faster at the boundaries. Greedy Training. τ+ as ( τ+ = τ In the following derivation, we will omit the sample inde q for simplicity. In the main paper, we defined λ τ H H + I + γ τ σ0 ik B τ ik B τ ik ) λ τ K (K τ y) + τ σ0 ik F ik τ ŵi τ ep F τ ik τ µ (σ +σ ) = τ (Λ τ ) η τ (50) where we have λ τ = N y K τ + Mσ k, (5) Λ τ = λ τ H H + I + γ τ σ0 ik B τ ik B τ ik, (5) and η τ = λ τ K (K τ y) + τ σ0 ik F ik τ ŵ τ i ep F τ ik τ µ (σ + σ ). (53) In the stage τ, the gradient equals τ+ Θ τ = (Λ τ ) Λτ Θ τ (Λτ ) η τ + ητ Θ τ. (54) Hence, given the loss function for stage τ L(Θ τ ) = C τ+ ( τ+ GT ), (55) 3

4 we can get the gradient of the loss function with respect to Θ τ as Θ τ = L(Θτ ) τ+ Λ τ+ Θ τ = P τ+ τ Θ τ (Λτ ) η τ ητ Θ τ η = P τ+ τ Θ τ + Λτ Θ τ (τ+ τ ), (56) where we define P τ+ = ( τ+ GT ) (C τ+ ) C τ+ (Λ τ ). Now we can obtain the derivative with respect to each parameter to be learned, i.e. σ, γ τ, ŵi τ and f i τ. To calculate L(Θτ ) σ, we can first take the derivative L(Θτ ) λ, after which τ can be easily calculated by chain rule σ Hence, we get σ γ τ ŵ τ i λ τ = P τ+ K (K τ y) + H H( τ+ τ ). (57) = L(Θτ ) λ τ λ τ σ P τ+ ik = P τ+ ik = P τ+ k λ τ σ = σnm k ( y K τ + Mσ k ). (58) F ik τ ŵ τ i ep F τ ik τ µ (σ + σ ) F τ ik τ µ σ (σ + σ ), (59) B τ ik B τ ik( τ+ τ ), (60) (F τ ik) ep F τ ik τ µ (σ + σ ). (6) We omit the derivation of L(Θτ ) f here. Since our work and shrinkage fields 5 make use of filters in the same way, the i τ derivation is analogous. For details we refer to the supplementary material of 5. Joint Training. After training each stage separately, we perform a oint training similarly to shrinkage fields 5 and the diffusion network 4, to which we refer to for more details. E. Additional Eperimental Results In Table 7, 8 and 9 we show additional results with both the PSNR and metrics and intermediate results of our GradNet (after st stage and 4 th stage). We also show two more visual results in Figs. 6 and 7 at the % and % noise levels corresponding to σ = 5.0 and.55. We can see that GradNet removes more blur in the flower region in Fig. 6. In the 3 rd row of Fig. 7 we also show the globally contrast-adusted difference between each reconstruction and the ground truth. We can see that GradNet compares favorably to EPLL on the dataset of Sun et al. Our noise-adaptive formulation is also able to deal with colored (spatially correlated) noise. We generate different amounts of white Gaussian noise %, 3%, and 4% (i.e., σ = 5.0, 7.65, 0.0), convolve these noise images with a 3 3 uniform filter to make noise spatially correlated and then finally add them to the blurry image. Eperiments are performed with 3 test images from 6. Results in Table 6 show that our noise-adaptive formulation is robust to colored noise. PSNR Method σ = 5.0 σ = 7.65 σ = 0. σ = 5.0 σ = 7.65 σ = 0. FD3 (non-blind) EPLL 37 + NE EPLL 37 + NA TV-L + NA BD GradNet 7S Table 6. Average PSNR(dB) and on 3 images from 6 for three different colored noise levels. 4

5 PSNR Method σ =.55 σ = 5.0 σ = 7.65 σ = 0. σ =.55 σ = 5.0 σ = 7.65 σ = 0. FD 3 (non-blind) RTF 4 (σ =.55) CSF 5 (non-blind) TNRD 4 (non-blind) TV-L (non-blind) EPLL 37 (non-blind) EPLL 37 + NE EPLL 37 + NA TV-L + NA BD GradNet S GradNet 4S GradNet 7S Table 7. Average PSNR (db) on 3 test images from 6. PSNR Method σ =.55 σ = 5.0 σ = 7.65 σ = 0. σ =.55 σ = 5.0 σ = 7.65 σ = 0. FD 3 (non-blind) EPLL 37 (non-blind) CSF 5 (non-blind) TNRD 4 (non-blind) EPLL 37 + NE EPLL 37 + NA TV-L + NA GradNet S GradNet 4S GradNet 7S Table 8. Average PSNR (db) on 640 test images from 9. PSNR Method σ =.55 σ = 5.0 σ = 7.65 σ = 0. σ =.55 σ = 5.0 σ = 7.65 σ = 0. FD 3 (non-blind) EPLL 37 (non-blind) RTF 4 (σ =.55) CSF 5 (non-blind) TNRD 4 (non-blind) EPLL 37 + NE EPLL 37 + NA TV-L + NA GradNet S GradNet 4S GradNet 7S Table 9. Average PSNR (db) on 50 test images from Berkeley segmentation dataset with large blurs. 5

6 (a) Blurry input (b) Ground Truth (c) TV-L (d) FD 3 (e) EPLL 37 (f) GradNet stage (g) GradNet 4 stage (h) GradNet 7 stage Figure 6. Results for the % noise case. PSNR results are also shown at the top left corner of the estimated images. (a) Blurry input (b) Ground Truth (c) TV-L (d) FD 3 (e) EPLL 37 (f) GradNet stage (g) GradNet 4 stage (h) GradNet 7 stage (i) Difference between EPLL and GT () Difference between FD and GT (k) Difference between TV and GT (l) Difference between GradNet and GT Figure 7. Results for the % noise case (best viewed on screen). PSNR results are also shown at the top left corner of the estimated images. 6