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A content-aware quantisation mechanism for transform domain distributed video coding
The discrete cosine transform (DCT) is widely applied in modern codecs to remove spatial redundancies, with the resulting DCT coefficients being quantised to achieve compression as well as bit-rate control. In distributed video coding (DVC) architectures like DISCOVER, DCT coefficient quantisation is traditionally performed using predetermined quantisation matrices (QM), which means the compression is heavily dependent on the sequence being coded. This makes bit-rate control challenging, with the situation exacerbated in the coding of high resolution sequences due to QM scarcity and the non-uniform bit-rate gaps between them. This paper introduces a novel content-aware quantisation (CAQ) mechanism to overcome the limitations of existing quantisation methods in transform domain DVC. CAQ creates a frame-specific QM to reduce quantisation errors by analysing the distribution of DCT coefficients. In contrast to the predetermined QM that is applicable to only 4x4 block sizes, CAQ produces QM for larger block sizes to enhance compression at higher resolutions. This provides superior bit-rate control and better output quality by seeking to fully exploit the available bandwidth, which is especially beneficial in bandwidth constrained scenarios. In addition, CAQ generates superior perceptual results by innovatively applying different weightings to the DCT coefficients to reflect the human visual system. Experimental results corroborate that CAQ both quantitatively and qualitatively provides enhanced output quality in bandwidth limited scenarios, by consistently utilising over 90% of available bandwidth
Automatic instantiation of abstract tests on specific configurations for large critical control systems
Computer-based control systems have grown in size, complexity, distribution
and criticality. In this paper a methodology is presented to perform an
abstract testing of such large control systems in an efficient way: an abstract
test is specified directly from system functional requirements and has to be
instantiated in more test runs to cover a specific configuration, comprising
any number of control entities (sensors, actuators and logic processes). Such a
process is usually performed by hand for each installation of the control
system, requiring a considerable time effort and being an error prone
verification activity. To automate a safe passage from abstract tests, related
to the so called generic software application, to any specific installation, an
algorithm is provided, starting from a reference architecture and a state-based
behavioural model of the control software. The presented approach has been
applied to a railway interlocking system, demonstrating its feasibility and
effectiveness in several years of testing experience
Fairness Testing: Testing Software for Discrimination
This paper defines software fairness and discrimination and develops a
testing-based method for measuring if and how much software discriminates,
focusing on causality in discriminatory behavior. Evidence of software
discrimination has been found in modern software systems that recommend
criminal sentences, grant access to financial products, and determine who is
allowed to participate in promotions. Our approach, Themis, generates efficient
test suites to measure discrimination. Given a schema describing valid system
inputs, Themis generates discrimination tests automatically and does not
require an oracle. We evaluate Themis on 20 software systems, 12 of which come
from prior work with explicit focus on avoiding discrimination. We find that
(1) Themis is effective at discovering software discrimination, (2)
state-of-the-art techniques for removing discrimination from algorithms fail in
many situations, at times discriminating against as much as 98% of an input
subdomain, (3) Themis optimizations are effective at producing efficient test
suites for measuring discrimination, and (4) Themis is more efficient on
systems that exhibit more discrimination. We thus demonstrate that fairness
testing is a critical aspect of the software development cycle in domains with
possible discrimination and provide initial tools for measuring software
discrimination.Comment: Sainyam Galhotra, Yuriy Brun, and Alexandra Meliou. 2017. Fairness
Testing: Testing Software for Discrimination. In Proceedings of 2017 11th
Joint Meeting of the European Software Engineering Conference and the ACM
SIGSOFT Symposium on the Foundations of Software Engineering (ESEC/FSE),
Paderborn, Germany, September 4-8, 2017 (ESEC/FSE'17).
https://doi.org/10.1145/3106237.3106277, ESEC/FSE, 201
Mistakes in medical ontologies: Where do they come from and how can they be detected?
We present the details of a methodology for quality assurance in large medical terminologies and describe three algorithms that can help terminology developers and users to identify potential mistakes. The methodology is based in part on linguistic criteria and in part on logical and ontological principles governing sound classifications. We conclude by outlining the results of applying the methodology in the form of a taxonomy different types of errors and potential errors detected in SNOMED-CT
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