Submitted by
Assigned_Reviewer_5
Q1: Comments to author(s).
First provide a summary of the paper, and then address the following
criteria: Quality, clarity, originality and significance. (For detailed
reviewing guidelines, see
http://nips.cc/PaperInformation/ReviewerInstructions)
This paper uses deep neural networks to denoise
images. The network uses several independent columns trained on different
types of noise. Furthermore, a weight prediction module is trained to
decide how to merge these columns to predict the clean image from the
noisy image. The idea is to have only one network for all types of noises
and noise strengths.
Noise is not always Gaussian, and it may
sometimes be beneficial to have a single method that can adapt to
different noise types. Engineered methods like BM3D are hard to modify to
arbitrary noise types, learned methods like Burger et al. have to be
retrained (or also the missing citation Jancsary et al., "Loss-Speci fic
Training of Non-Parametric Image Restoration Models"). This method
solves it by training different models on different noises and then
combining the results. The method is shown to be successful in denoising
different types of noises after a one-time training. Denoising also works
on "unseen" noise that wasn't trained on in any of its submodels.
However, it is inferior to just training on a single noise type for
that specific noise type: SSDA outperforms MC-SSDA on the CT images on
Gaussian noise type 2 and 3, which have similar PSNR to the training PSNR
of SSDA. The same holds true for the MNIST comparison. Furthermore, the
SSDA is also able to denoise unseen noise types to some extent, in one
case even better. [The authors were able to address this issue during the
rebuttal by training a new model with additional columns.] Also, it's
not compared to standard denoising methods on natural images, which I
would expect. On digital photos the noise usually is a mixture of Gaussian
and Poisson noise, which the method should be able to handle. I wonder
what the runtime of the method is (training/testing)? Also, how does the
performance change if the number of autoencoders is varied?
The
paper is well structured and easy to understand. Very beneficial is that
the code would be published after publication.
Q2: Please summarize your review in 1-2
sentences
This paper learns a single neural network to denoise
several types of noises. This works, however it's a trade-off compared to
using an algorithm for one specific noise type. Submitted by
Assigned_Reviewer_6
Q1: Comments to author(s).
First provide a summary of the paper, and then address the following
criteria: Quality, clarity, originality and significance. (For detailed
reviewing guidelines, see
http://nips.cc/PaperInformation/ReviewerInstructions)
This paper explores combining multiple towers of
stacked sparse denoising autoencoders. Simple averaging of towers like in
Ciresan does for classification cannot work for denoising so authors
instead predict the weights used to linearly combine the towers. The
weight predictor is a RBF network with regression given the tower
features.
Experiments with both qualitative and quantitative
results are convincing (classification and denoising) and MC-SSDA does
provide a good improvement over single SSDA.
Quality: good,
multiple experiments, different tasks. Clarity: good. Originality:
reusing non-novel pieces and multiple towers have been used for
classification, but I don't know that it has for denoising.
Significance: might be of significance for medical imaging
community. Q2: Please summarize your review in 1-2
sentences
Good paper, no new ideas but good
results. Submitted by
Assigned_Reviewer_7
Q1: Comments to author(s).
First provide a summary of the paper, and then address the following
criteria: Quality, clarity, originality and significance. (For detailed
reviewing guidelines, see
http://nips.cc/PaperInformation/ReviewerInstructions)
This paper proposes the use of multiple columns
(networks), with proper weighting, for image denoising. The multiple
columns allow for the ability to denoise many different types of noise
without knowing which noise type at test time.
An RBF network is
learned to predict the weighting of the contribution of different columns,
which is similar to mixture of experts.
Line 88-89: The citation
of Hinton et al. transforming autoencoders is not appropriate here.
Transforming autoencoders is about learning transformations and have
nothing to do with denoising.
A criticism of this method is that
you are training with known noise processes. A lot of the work in
denoising literature is learning models without having the ability to
generate clean-corrupt pairs of training images. Another is that the
network is c times slower, where c is the number of the columns.
The experimental results demonstrate good performance on MNIST
images and medical image datasets. An additional recommendation is to use
real noise instead of synthetic noise added by
'imnoise'. Q2: Please summarize your review in 1-2
sentences
This paper demonstrates superior performance in
denoising by using multiple columns of neural net to handle multiple types
of noise. Experimental results show improvement over the single column
variants.
Q1:Author
rebuttal: Please respond to any concerns raised in the reviews. There are
no constraints on how you want to argue your case, except for the fact
that your text should be limited to a maximum of 6000 characters. Note
however that reviewers and area chairs are very busy and may not read long
vague rebuttals. It is in your own interest to be concise and to the
point.
We thank all reviewers for helpful comments.
1. Novelty of our method: As Reviewer 6 pointed out, the
conventional way of combining multi-column deep networks by simple
averaging does not work well when the distribution of training data does
not match the distribution of test data. The key novelty of our method is
to address this limitation by (1) computing optimal column weights via
solving a quadratic program and (2) training a separate network to predict
the optimal weights. Our method is generally applicable to not only
denoising, but also many other problems.
2. Regarding
comparison to SSDA: To address the concern that our method was a
"trade-off compared to using an algorithm for one specific type of noise,"
we trained a 21 column AMC-SSDA. In our experiments, this single AMC-SSDA
outperformed (on average) other baseline SSDAs trained from any specific
type of noise (e.g., Gaussian, salt & pepper, or speckle) or the
mixture of all these noise types.
In additional control
experiment, for each "seen" noise type that was tested on in the paper, we
trained an SSDA with that exact noise type, including the exact statistics
of the noise; let's call this the "informed-SSDA". Please note that this
setting provides an unfair advantage to the informed-SSDA since we do not
provide information about the noise type or statistics in testing time to
any other methods evaluated in the paper.
Even in this case, the
AMC-SSDA still performed comparably to the informed-SSDA. Specifically,
the AMC-SSDA performed slightly better on the Gaussian noise or Salt &
Pepper noise, and slightly worse for Speckle noise. On average, the
informed-SSDA had a PSNR that was only slightly better than the AMC-SSDA.
Using the two-tailed paired t-test, the p-value we obtained was 0.47,
showing that there is not a statistically significant difference between
these two methods. This suggests that the AMC-SSDA can perform as well as
using an "ideally" trained network for specific noise type (i.e., training
and testing an SSDA for the same specific noise type).
In
addition, our single AMC-SSDA achieved classification error rates better
than (up to 0.22%) or comparable to (within 0.06% difference) the
corresponding informed-SSDAs.
3. Performance with varying
number of columns: In our experiments, we found that the increased
number of column leads to better performance. For example, the AMC-SSDA
with 21 columns had, on average, a PSNR that was significantly higher than
the AMC-SSDA with 9 columns (i.e., 0.45dB higher on average, with p-value
of 0.001).
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