128,046 research outputs found
A simple online competitive adaptation of Lempel-Ziv compression with efficient random access support
We present a simple adaptation of the Lempel Ziv 78' (LZ78) compression
scheme ({\em IEEE Transactions on Information Theory, 1978}) that supports
efficient random access to the input string. Namely, given query access to the
compressed string, it is possible to efficiently recover any symbol of the
input string. The compression algorithm is given as input a parameter \eps
>0, and with very high probability increases the length of the compressed
string by at most a factor of (1+\eps). The access time is O(\log n +
1/\eps^2) in expectation, and O(\log n/\eps^2) with high probability. The
scheme relies on sparse transitive-closure spanners. Any (consecutive)
substring of the input string can be retrieved at an additional additive cost
in the running time of the length of the substring. We also formally establish
the necessity of modifying LZ78 so as to allow efficient random access.
Specifically, we construct a family of strings for which
queries to the LZ78-compressed string are required in order to recover a single
symbol in the input string. The main benefit of the proposed scheme is that it
preserves the online nature and simplicity of LZ78, and that for {\em every}
input string, the length of the compressed string is only a small factor larger
than that obtained by running LZ78
Finger Search in Grammar-Compressed Strings
Grammar-based compression, where one replaces a long string by a small
context-free grammar that generates the string, is a simple and powerful
paradigm that captures many popular compression schemes. Given a grammar, the
random access problem is to compactly represent the grammar while supporting
random access, that is, given a position in the original uncompressed string
report the character at that position. In this paper we study the random access
problem with the finger search property, that is, the time for a random access
query should depend on the distance between a specified index , called the
\emph{finger}, and the query index . We consider both a static variant,
where we first place a finger and subsequently access indices near the finger
efficiently, and a dynamic variant where also moving the finger such that the
time depends on the distance moved is supported.
Let be the size the grammar, and let be the size of the string. For
the static variant we give a linear space representation that supports placing
the finger in time and subsequently accessing in time,
where is the distance between the finger and the accessed index. For the
dynamic variant we give a linear space representation that supports placing the
finger in time and accessing and moving the finger in time. Compared to the best linear space solution to random
access, we improve a query bound to for the static
variant and to for the dynamic variant, while
maintaining linear space. As an application of our results we obtain an
improved solution to the longest common extension problem in grammar compressed
strings. To obtain our results, we introduce several new techniques of
independent interest, including a novel van Emde Boas style decomposition of
grammars
RLFC: Random Access Light Field Compression using Key Views and Bounded Integer Encoding
We present a new hierarchical compression scheme for encoding light field
images (LFI) that is suitable for interactive rendering. Our method (RLFC)
exploits redundancies in the light field images by constructing a tree
structure. The top level (root) of the tree captures the common high-level
details across the LFI, and other levels (children) of the tree capture
specific low-level details of the LFI. Our decompressing algorithm corresponds
to tree traversal operations and gathers the values stored at different levels
of the tree. Furthermore, we use bounded integer sequence encoding which
provides random access and fast hardware decoding for compressing the blocks of
children of the tree. We have evaluated our method for 4D two-plane
parameterized light fields. The compression rates vary from 0.08 - 2.5 bits per
pixel (bpp), resulting in compression ratios of around 200:1 to 20:1 for a PSNR
quality of 40 to 50 dB. The decompression times for decoding the blocks of LFI
are 1 - 3 microseconds per channel on an NVIDIA GTX-960 and we can render new
views with a resolution of 512X512 at 200 fps. Our overall scheme is simple to
implement and involves only bit manipulations and integer arithmetic
operations.Comment: Accepted for publication at Symposium on Interactive 3D Graphics and
Games (I3D '19
Bandwidth compression of sonar displays
A major problem affecting the design of data compression systems
is that of employing a buffer of limited size and at the same time
prevent uncontrollable loss of data due to overflow. One method of
alleviating this problem is to employ an adaptive compression algorithm.
With this design approach when overflow is imminent the compression
algorithm is degraded which effectively reduces the input rate to the
buffer.
A method is proposed here, where by using a recirculating register
as the buffer the recirculating data controls the input rate and hence
the performance of the system.
The system has been analysed for a Poisson input process, and
simulated using synthetic patterns similar to that encountered on sonar
displays. The results indicate that this form of storage is quantitatively
similar to random-access storage but qualitatively superior due
to the random nature of the losses.
An experimental system has been built using dynamic MOS shift
registers for the store and a simple run-length coding procedure
IBVC: Interpolation-driven B-frame Video Compression
Learned B-frame video compression aims to adopt bi-directional motion
estimation and motion compensation (MEMC) coding for middle frame
reconstruction. However, previous learned approaches often directly extend
neural P-frame codecs to B-frame relying on bi-directional optical-flow
estimation or video frame interpolation. They suffer from inaccurate quantized
motions and inefficient motion compensation. To address these issues, we
propose a simple yet effective structure called Interpolation-driven B-frame
Video Compression (IBVC). Our approach only involves two major operations:
video frame interpolation and artifact reduction compression. IBVC introduces a
bit-rate free MEMC based on interpolation, which avoids optical-flow
quantization and additional compression distortions. Later, to reduce duplicate
bit-rate consumption and focus on unaligned artifacts, a residual guided
masking encoder is deployed to adaptively select the meaningful contexts with
interpolated multi-scale dependencies. In addition, a conditional
spatio-temporal decoder is proposed to eliminate location errors and artifacts
instead of using MEMC coding in other methods. The experimental results on
B-frame coding demonstrate that IBVC has significant improvements compared to
the relevant state-of-the-art methods. Meanwhile, our approach can save bit
rates compared with the random access (RA) configuration of H.266 (VTM). The
code will be available at https://github.com/ruhig6/IBVC.Comment: Submitted to IEEE TCSV
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