Handling Noise in Single Image Deblurring using Directional Filters

Handling Noise in Single Image Deblurring using Directional Filters
2013 IEEE Conference on Computer Vision and Pattern Recognition
Handling Noise in Single Image Deblurring using Directional Filters
Lin Zhong1 Sunghyun Cho2 Dimitris Metaxas1 Sylvain Paris2 Jue Wang2
Rutgers University
Adobe Research
Many single image blind deconvolution methods have
been recently proposed [4, 6, 8–10, 13, 14, 16, 20]. Although
they generally work well when the input image is noise-free,
their performance degrades rapidly when the noise level increases. Specifically, the blur kernel estimation step in previous deblurring approaches is often too fragile to reliably
estimate the blur kernel when the image is contaminated
with noise, as shown in Fig. 1. Even assuming that an accurate blur kernel can be estimated, the amplified image noise
and ringing artifacts generated from the non-blind deconvolution also significantly degrade the results [5, 11, 21, 22].
State-of-the-art single image deblurring techniques are
sensitive to image noise. Even a small amount of noise,
which is inevitable in low-light conditions, can degrade the
quality of blur kernel estimation dramatically. The recent
approach of Tai and Lin [17] tries to iteratively denoise and
deblur a blurry and noisy image. However, as we show in
this work, directly applying image denoising methods often partially damages the blur information that is extracted
from the input image, leading to biased kernel estimation.
We propose a new method for handling noise in blind
image deconvolution based on new theoretical and practical insights. Our key observation is that applying a directional low-pass filter to the input image greatly reduces the
noise level, while preserving the blur information in the orthogonal direction to the filter. Based on this observation,
our method applies a series of directional filters at different
orientations to the input image, and estimates an accurate
Radon transform of the blur kernel from each filtered image.
Finally, we reconstruct the blur kernel using inverse Radon
transform. Experimental results on synthetic and real data
show that our algorithm achieves higher quality results than
previous approaches on blurry and noisy images. 1
To handle noisy inputs in single image deblurring, Tai
and Lin [17] first apply an existing denoising package [1]
as preprocessing, and then estimate the blur kernel and the
latent image from the denoised result. This process iterates
a few times to produce the final result. However, applying
existing denoising methods is likely to damage, at least partially, the detailed blur information that one can extract from
the input image, thereby leading to a biased kernel estimation. In Sec. 2, we illustrate that standard denoising methods, from bilateral filtering to more advanced approaches
such as Non-Local Means [3] and BM3D [7], have negative
impacts on the accuracy of kernel estimation.
In this paper, we propose a new approach for estimating
an accurate blur kernel from a noisy blurry image. Our approach still involves denoising and deblurring steps. However, we carefully design the denoising filters and deblurring procedures in such a way that the estimated kernel is
not affected by the denoising filters. That is, we shall see
that, unlike existing approaches, we can theoretically guarantee that our approach does not introduce any bias in the
estimated kernel.
1. Introduction
Taking handheld photos in low-light conditions is challenging. Since less light is available, longer exposure times
are needed – and without a tripod, camera shake is likely to
happen and produce blurry pictures. Increasing the camera
light sensitivity, i.e., using a higher ISO setting, can reduce
the exposure time, which helps. But it comes at the cost of
higher noise levels. Further, this is often not enough, and
exposure time remains too long for handheld photography,
and many photos end up being blurry and noisy. Although
many techniques have been proposed recently to deal with
camera shake, most of them assume low noise levels. In this
work, we do not make this assumption and aim to restore a
sharp image from a blurry and noisy input.
Our approach is derived from the key observation that
if a directional low-pass linear filter is applied to the input
image, it can reduce the noise level greatly, while the frequency content, including essential blur information, along
the orthogonal direction is not affected. We use this property to estimate 1D projections of the desired blur kernel to
the orthogonal directions of these filters. These projections,
also known as the Radon transform, will not be affected
by applying directional low-pass filters to the input image,
except for the noise reduction. Based on this observation,
1 This work was performed when the first author interned at Adobe Research.
1063-6919/13 $26.00 © 2013 IEEE
DOI 10.1109/CVPR.2013.85
(a) Input
(c) Levin et al. [15]
(b) Cho and Lee [4]
(d) Our method
Figure 1. Previous deblurring methods are sensitive to image noise. (a) Synthetic input image with 5% noise and the ground truth kernel
(overlayed). It is cropped to better show blur and noise. (b) Estimated kernel and latent image by Cho and Lee [4]. (c) Results by Levin et
al. [15]. (d) Results of our method.
the relative error of k with respect to the noise in b using
the condition number of the linear system, that is:
we apply a series of directional low-pass filters at different
orientations, and estimate a slice of kernel projection from
each image. This yields an accurate estimate of the Radon
transform. Finally, we reconstruct the blur kernel using the
inverse Radon transform. Once a good kernel is obtained,
we incorporate denoising filtering into the final deconvolution process to suppress noise and obtain a high-quality
latent image. Results on synthetic and real noisy data show
that our method is more robust and achieves better results
than previous approaches.
(LT L)−1 LT n/(LT L)−1 LT b =
LT n/LT b ≤ (LT L) · (LT L)−1 = κ(LT L),
where e(k) and e(b) are relative errors in k and b, respectively. Thus, the noise n in the input image will be amplified
at most by the condition number κ(LT L) for kernel estimation, where LT L is often called the deconvolution matrix and has a block-circulant-with-circulant-block (BCCB)
structure [12]. Eq. 4 shows that the upper bound on the error in the estimated kernel is proportional to the amplitude
of the noise in input image. Building on this result, one can
attempt to apply sophisticated denoising filter to the blurry
image to reduce the noise amplitude, hoping that this will
improve the kernel estimate. However, denoising filters also
alter the profile of edges, e.g., [2]. This information is critical to accurate kernel estimation, and as we shall see, the
benefits of the noise reduction are often outweighed by the
artifacts caused by the profile alteration.
To illustrate it, we first look at a simple noise reduction
method, Gaussian smoothing. Convolving with a Gaussian
Gg decreases the noise level. However, the kernel estimation then becomes:
2. Side effects of denoising as preprocessing
Before introducing our approach, we first analyze the
negative impact of employing denoising as preprocessing
on kernel estimation. In single image deblurring, a blurry
and noisy input image b is usually modeled as:
∗ k + n,
where , k and n represent the latent sharp image, blur kernel, and additive noise, respectively, ∗ is the convolution
operator. Solving and k from input b is a severely illposed problem, and the additional noise n makes this problem even more challenging.
Assuming that is known, a common approach to solve
for k is:
k = argmink b − k ∗ 2 + ρ(k) ,
where ρ(k) is the additional regularization term that imposes smoothness and/or sparsity prior on k. Without
considering the regularization term, this becomes a leastsquares problem and the optimal k can be found by solving
the following linear system:
LT Lk = LT b = LT (b + n),
argminkg b ∗ Gg − ∗ kg 2
argminkg ( ∗ k + n) ∗ Gg − ∗ kg 2
argminkg ∗ (k ∗ Gg − kg )2 = k ∗ Gg , (5)
where k is the blur kernel for the original input image and
kg is the optimal solution after Gaussian denoising. Eq. 5
shows that the estimated kernel kg is a blurred version of
the actual kernel k. Further, since Gg is a low-pass filter,
the high frequencies of k are lost and recovering them from
kg would be very difficult, if possible at all. This result
comes from the initial noise reduction and is independent
of the kernel estimation method.
where k and b are the corresponding vector forms of k and
b, respectively, and L is the matrix form of . We also introduce the noise-free blurry image b = b − n. We estimate
(a) Input
(b) True kernel
(c) No denoising
(d) Gaussian filter
(e) Bilateral filter
(f) Non-local means
(g) BM3D
(h) Our method
Figure 2. The side effects of employing different denoising methods as preprocessing step in single image deblurring. (a) the synthetic
input image with 5% noise. (b) the ground truth kernel. (c) the blur kernel estimated without applying any denoising method to the input
image (a). (e)-(g) the estimated blur kernels after applying different denoising filters. (h) the kernel estimated by our method.
where I is an image, p is a pixel location, t is the spatial
distance from one
pixel to p, c is the normalization factor
defined as c = −∞ w(t)dt, and uθ = (cos θ, sin θ)T is
a unit vector of direction θ. The profile of the filter is determined by w(t), for which we use a Gaussian function:
w(t) = exp(−t2 /2σf2 ), where σf controls the strength of
the filter.
Filtering the image affects the estimated kernel. With
the same argument as for Eq. 5, the kernel that we estimate
from the filtered image bθ = b ∗ fθ is:
Although more sophisticated denoising methods are better at preserving high frequencies, denoising remains an
open problem for which no perfect solution exists. Since no
information about the blur kernel can be observed in uniform regions of the blurry image, edges are the main source
of information that drives deblurring algorithms either implicitly or explicitly, e.g., [4, 6, 10, 20]. Even small degradations introduced by state-of-the-art denoising techniques
can have a strong impact on deblurring results as shown in
Fig. 2. In this experiment, we apply bilateral filtering [19],
non-local means [3] and BM3D [7] to a test image with 5%
noise, i.e., noise of standard deviation 0.05 when the intensity range is [0, 1], and then use Cho and Lee’s method [4]
to estimate the blur kernel. The estimated kernels are not
accurate due to the side effects of denoising.
The recent approach of Tai and Lin [17] first applies
an existing commercial denoising package (NeatImage [1])
to the input image, then iteratively applies a motion-aware
non-local mean filtering and deblurring to refine the results.
Although special treatment has been added into the process,
both the commercial denoising package and the non-local
means filter have the same negative impacts on kernel estimation as we will show in Sec. 4.
k ∗ fθ .
Similarly to filtering with a 2D Gaussian Gg , applying fθ
averages pixels and reduces the noise level. Since fθ filters
only along the direction θ, it has nearly no influence on the
blur information in the orthogonal direction. We exploit this
property to estimate the projection of the original kernel k
along the direction θ. The projection can be formulated as
Radon transform [6, 18], which is the collection of integrals
of a signal (i.e., k) along projection lines. The particular
value on Radon transform corresponding to one projection
line ρ = x sin(θ) + y cos(θ) is:
Rθ (ρ) =
k(x, y)δ(ρ − x sin(θ) − y cos(θ))dxdy,
3. Our approach
where k(x, y) indicates the value at the coordinate (x, y) on
kernel k. θ and ρ are the angle and offset of the projection
line, respectively. Thus, the projection of kernel kθ along
the projection direction θ is:
In the previous section, we have shown that there is a
tension between noise reduction and edge preservation. The
former helps to estimate a more accurate kernel, but the latter hinders it. Our experiments showed that even state-ofthe-art denoising filters do have negative impacts on kernel
estimation. In this section, we resolve this problem by using directional blur and the Radon transform to estimate the
kernel. Our approach reduces the noise without degrading
blur information, thereby producing better kernels.
Rθ (kθ ) = Rθ (k ∗ fθ ) = Rθ (k) ∗ Rθ (fθ ) = Rθ (k), (9)
where Rθ (·) is the Radon transform operator to the direction θ , and θ = θ + π/2. It is a linear operator, and one
can verify that Rθ (fθ ) is a 1D delta function, given the
definition of fθ (Eq. 6). Eq. 9 shows fθ has no impact on
the Radon transform of the blur kernel to the orthogonal direction of the filter. This is the foundation of the proposed
approach. An example is shown in Fig. 3.
3.1. Applying directional filters
We now show that directional low-pass filters can be applied to an image without affecting its Radon transform,
while decreasing its noise level. We consider the directional
low-pass filter fθ :
1 ∞
w(t)I(p + tuθ )dt,
I(p) ∗ fθ =
c −∞
3.2. The algorithm
We now explain how we recover the sharp image, with
the kernel estimation first, and then the deconvolution step.
No noise
Noisy + filter
Algorithm 1 Multiscale noise-aware blind deconvolution
Input: The pyramid {b0 , b1 , ..., bn } by down-sampling the
input blurry and noisy image b, where b0 = b.
Output: blur kernel k0 and latent image 0 .
Directional filter
Figure 3. Directional denoising mechanism in single image deblurring. (a)(b)(c) are the synthetic image before adding noise, after adding noise, and after applying a directional filter(θ = 3π/4),
respectively. (d)(e)(f) are the corresponding estimated blur kernels and their Radon transforms in the same direction. Note that
the estimated kernel in (f) is largely damaged by the directional
filter, but its Radon transform is the same as the one in (d).
3.2.1 Noise-aware kernel estimation
Based on the above analysis, we apply a directional blur fθ ,
estimate the combined blur kernel kθ , and then project it
along the same direction of the filter to get the corresponding Radon transform. We repeat this process to get a set of
projections. Finally, we compute the 2D kernel using the
inverse Radon transform [18]. The advantage of this strategy is that it greatly reduces noise when applying fθ , while
keeping the computed Radon transform intact. However, so
far, we have assumed that the latent image is known when
estimating the blur kernels. This is not the case in practice,
and even with state-of-the-art kernel estimation techniques,
recovering kθ from bθ , which is a blurry image convolved
with an additional directional blur, has proven to be challenging. The additional filter tends to make nearby edges
“collide” with each other, which in turn introduces errors in
the estimated kernel.
For a more reliable kernel estimation, we adopt the multiscale blind deconvolution framework commonly used in
previous approaches [4, 20]. We create an image pyramid
of the input image b as {b0 , b1 , ..., bn }, where b0 is the original resolution, and estimate the blur kernel in a bottom-up
fashion from bn to b0 . Since noise is largely removed by
image downsizing, we apply an existing approach by Cho
and Lee [4] to estimate the blur kernels ki and latent images
i from layer bn to b1 . Only for the full resolution layer
b0 , we apply the directional filter fθ and then estimate the
Apply an existing nonblind approach ( [4] in our implementation) to estimate ki and i for bi ,i = n, ..., 1.
Upsample 1 to generate initial 0 .
Apply Nf directional filters to the input image b0 ,
each filter has a direction of i · π/Nf , i = 1, ..., Nf ,
where Nf is the number of directional filters.
For each filtered image bθ , use 0 as the latent image
to estimate kθ .
For each optimal kernel kθ , compute its Radon transform Rθ (kθ ) as in Eq. 9, along the direction θ =
θ + π/2.
Reconstruct k0 from the series of Rθ (kθ ) using inverse Radon transform.
Update 0 based on the new k0 using a noise-aware
nonblind deconvolution approach.
until k0 converges.
With the final estimated kernel k0 , use the final deconvolution method described in Sec. 3.2.2 to generate the
final output 0 .
kernel using the robust deconvolution technique described
later in this section. The process is described in Algorithm
1. Steps 4 to 7 are also illustrated in Fig. 4. Specifically, in
Step 5, although each filtered image bθ is severely blurred
with the additional filtering, the latent image 0 , initialized
from the multiscale process, is relatively sharp and clean,
which allows us to estimate kθ as:
kθ = argminkθ ∇bθ − kθ ∗ ∇0 2 + ρ(kθ ) , (10)
where ∇ is the gradient operator. This process is robust to
noise because ∇bθ is a low-pass filtered image. In Step 8,
nonblind deconvolution is employed to update 0 based on
the new k0 . However, existing methods do not work well in
this case since we need to estimate a clean 0 from a noisy
image b0 , and the results of previous methods are prone to
inaccuracy. To generate a noise-free 0 , we minimize the
following energy function that aims for limiting the impact
of noise on the result:
∇0 ∗ k0 − ∇b0 2 + w1 ∇0 − u(∇1 )2 + w2 ∇0 2 ,
where u(·) is the upsampling function, and w1 and w2 are
pre-defined weights. The second term encourages the gradient of 0 to be similar to the upsampled gradient field of
PSF Reconstruction
(a) Input image
Figure 4. Illustration of applying directional filters for blur kernel
estimation from a noisy input image. We apply directional filters
in different orientations to the input image. From each filtered image a corresponding kernel is computed first, then projected along
the same direction to generate the correct radon transform of the
true kernel. The final blur kernel k0 is reconstructed using inverse
Radon transform [6].
(c) Zoran&Weiss [23]
(b) Estimated kernel
(d) Cho et al. [5]
(e) Our method
Figure 5. Comparison results of our final noise-aware nonblind
deconvolution with other recent nonblind deconvolution methods.
The results are obtained using the same input image and the estimated kernel. (c),(d),(e) show the zoom-in results.
1 , which is from the previous level in the pyramid. Since
1 contains much less noise due to image downsizing, incorporating this term can effectively reduce the noise level
in 0 . This non-blind deconvolution step is an intermediate
step in blur kernel estimation that produces sufficiently accurate images at a limited computational cost. In the next
section, we describe a more sophisticated non-blind deconvolution algorithm for generating high-quality final latent
image given the estimated kernel.
It is worth mentioning that for simplicity, in the above
discussion we assume b1 is almost noise-free after downsizing the image by half. However, this will not be true,
if severe noise presents in b0 . To deal with severe noise,
we will only use previous methods to estimate blur kernels
from bn to b2 in Step 1 of the algorithm, and then apply
noise-aware kernel estimation from Step 2 to 9 to the last
two layers b1 and b0 . We applied this modified version of
the algorithm to examples with 10% noise (Gaussian noise
with standard deviation of 0.1) in Sec. 4.
denoising methods in the process. This is in sharp contrast
to Tai and Lin’s method [17] where denoising and kernel
estimation interfere with each other.
In our approach, we minimize the following energy function to estimate the final 0 :
0 ∗ k0 − b0 2 + w3 0 − NLM(0 )2 ,
where NLM(·) is the non-local means denoising operation [3], and w3 is a balancing weight. Minimizing this energy function will ensure that the deblurred result is noisefree, and can best fit with k0 and b0 as well.
Directly minimizing this energy is hard because
NLM(0 ) is highly nonlinear. We found that iterating the
following two steps yields a good result in practice:
0 = NLM(0 ),
0 = argmin0 0 ∗ k0 − b0 + w3 0 − 0 .
Discussion Cho et al. [6] also use the Radon transform to
recover the blur kernel. However, their approach to compute the kernel projection is different from ours. They rely
on heuristics to identify straight edges in the images, and
extract the projections from these edges. Because this process relies on a few arbitrary thresholds to locate and analyze the edges, it is sensitive to noise. We also show that it
performs poorly on noisy inputs in the experimental section.
In comparison, our approach does not rely on such arbitrary
thresholds and performs well on noisy images.
For initialization, we set 0 to be zero (a black image). Solving Eq. 13b yields a noisy 0 that also contains useful highfrequency image structures. In the alternating minimization process, the noise in 0 is gradually reduced, while the
high-frequency image details are preserved. To show the
effectiveness of our method, we compare it with other two
recent non-blind deconvolution methods, i.e., Zoran and
Weiss [23] and Cho et al. [5] in Fig. 5.
4. Experimental results
Final noise-aware nonblind deconvolution
We implemented our method in Matlab on an Intel Core
i5 CPU with 8GB of RAM. We apply directional filters
along 36 regularly sampled orientations, that is, one sample every 5◦ . The computation time is a few minutes for a
one-megapixel image. For all the experiments, we set the
Once an accurate k0 is estimated, we use it to estimate
a good latent image 0 from the noisy input b0 . This is not
a trivial task when b0 contains severe noise [21]. However,
since k0 is fixed at this stage, it is safe to apply existing
(a) Abbey(input, 5% noise)
(b) Chalet(input, 5% noise)
(c) Aque(input,10% noise)
(f) Abbey (result, 5% noise)
(i) Abbey (result, 10% noise)
(d) Kernel 1
i d i
(g) Chalet (result, 5% noise)
(j) Chalet (result, 10% noise)
(e) Kernel 2
(h) Aque (result, 5% noise)
i d i
(k) Aque (result, 10% noise)
Figure 6. Comparing Tai and Lin’s method [17] and our method on synthetic data. Three input blurry image examples with different levels
of noise are shown in (a),(b),(c). (d) and (e) are the ground truth blur kernels from Levin et. al. [14]. (d) is used for the examples “Abbey”
and “Chalet”, and (e) is used for the example “Aque”. (f-k) show the estimated kernels and the latent images of Tai and Lin’s method and
our method with 5% noise and 10% noise. Due to the space limit only the areas highlighted by the bounding boxes in (a-c) are shown. Full
size images for comparison are in the supplementary material.
We first conducted experiments on images that we convolved with a known blur kernel and to which we added
noise in a controlled fashion. This allows us to report quantitative measures in addition to visual results.
mean and standard deviations of 0.05 and 0.1 for a [0,1]
intensity range. Tai and Lin kindly provided the results
for their method. The comparison shows that visually our
estimated blur kernels are closer to the ground truth, and
our estimated latent images contain more details and less
ringing artifacts. We also evaluate the results quantitatively
by computing the Peak Signal-to-Noise Ratio (PSNR) and
Structural SIMilarity (SSIM) (Table 1).
Comparisons with Tai and Lin’s method Tai and Lin’s
method [17] is the most related work to ours since it also
seeks to handle noisy images. This section focuses on comparing this method with our approach. We first ran comparisons on synthetic images (Fig. 6), where the latent sharp
images were blurred using two blur kernels provided by
Levin et al. [14]. We then added Gaussian noise with zero
Comparisons with other methods We also conducted
experiments to explore how noise affects the performance
of other state-of-the-art single-image blind deconvolution
methods. Using the “Aque” image and the blur kernel
shown in Fig. 6(e), we generated 10 input images with noise
from 1% to 10%. We then applied different blind deconvolution methods to these test images, and measure the PSNR
extent σf of the directional filter to 30 pixels. We also set
w1 = 0.05 and w2 = 1 (Eq. 11), and w3 = 0.05 (Eq. 12).
4.1. Synthetic data
22.43 21.05
22.73 21.61
19.79 18.95
22.80 19.35
26.58 24.53
28.46 25.58
ing artifacts. Overall, our approach produces visually more
satisfying results.
We further show our results on real-world photographs
that were captured under common low-light conditions with
a Nikon D90 DLSR camera and a 18 − 105mm lens.
We compare our results with those of other state-of-theart methods, including Goldstein and Fattal [9], Cho and
Lee [4], Cho et al. [6], Levin et al. [15]. The results (Fig. 9)
show that our recovered latent images exhibit less artifacts,
such as noise and ringing, and contain more high-frequency
details at the same time. These observations are consistent
across all test images. We provide additional examples in
supplemental material.
.8122 .7242
.8150 .7270
.8244 .7162
.8273 .7200
.8206 .7415
.8512 .7469
Table 1. The comparison experiments of our method and Tai and
Lin [17] on synthetic blurry images with different amount of
noises. The performances are evaluated by PSNR and SSIM, comparing the generated latent images with the ground truth.
Goldstein and Fattal
Cho and Lee
Cho et al.
Levin et al.
Tai and Lin
5. Conclusion
We have shown that most state-of-the-art image deblurring techniques are sensitive to image noise. In this paper,
we propose a new single image blind deconvolution method
that is more robust to noise than previous approaches. Our
method uses directional filters to reduce the noise while
keeping the blur information in their orthogonal direction
intact. By applying a series of such directional filters, we
showed how to recover correct 1D projections of the kernel
in all directions, which we use to estimate an accurate blur
kernel using the inverse Radon transform. We also introduced a noise-tolerant non-blind deconvolution technique
that generates high-quality final results. The effectiveness
of the proposed approach is demonstrated on several comparisons on synthetic and real data.
Noise level (%)
Figure 7. The PSNR curves of various blind deconvolution algorithms, including Goldstein and Fattal [9], Cho and Lee [4], Cho et
al. [6], Levin et al. [15] and our method, on the 10 synthetic test
images with noise level from 1% to 10%, generated by the “Aque”
image and the kernel shown in Fig. 6(e). The two data points of
Tai and Lin’s method [17] are shown as black diamonds, which
are provided by the authors. While the PSNR values are closer
to ours, the visual difference is still significant; our approach produces cleaner images (Fig. 8). All images are included in the supplementary material.
We would like to thank the anonymous reviewers for
their helpful feedback. This research is partially supported by the following grants to Dimitris Metaxasa: NSF1069258 and Adobe Systems.
curve of each method (Fig. 7). The accuracies of previous methods degrade rapidly when the noise level increases.
On the contrary, our method is more robust, i.e., it works
more reliably in the presence of noise, and achieves satisfactory results even when the input noise level is high. This
figure also includes two data points of the Tai and Lin’s
method [17] provided by the authors themselves.
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4.2. Results on real examples
We first compared our method and Tai and Lin’s method
on real-world images shown in their original paper [17], and
the results are shown in Fig. 8. The results of other state-ofthe-art methods can be found in [17]. Our estimated kernels
are sharper than Tai and Lin’s. The close-ups show that
our method recovers more high-frequency details. For the
boundaries of objects, our results have less noticeable ring-
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(a) Santorini
(b) Books
Figure 8. Comparisons of Tai and Lin’s method and our method on real-world images from [17]. Our results contain more high-frequency
details and less ringing artifacts. Zoom-in regions are shown in bounding boxes.
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Figure 9. Comparisons on real-world examples, where we compare our results with the results of Goldstein and Fattal [9], Cho and Lee [4],
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