Retinal image quality assessment through a visual similarity index

Retinal image quality is commonly analyzed through parameters inherited from instrumental optics. These parameters are defined for ‘good optics’ so they are hard to translate into visual quality metrics. Instead of using point or artificial functions, we propose a quality index that takes into account properties of natural images. These images usually show strong local correlations that help to interpret the image. Our aim is to derive an objective index that quantifies the quality of vision by taking into account the local structure of the scene, instead of focusing on a particular aberration. As we show, this index highly correlates with visual acuity and allows inter-comparison of natural images around the retina. The usefulness of the index is proven through the analysis of real eyes before and after undergoing corneal surgery, which usually are hard to analyze with standard metrics.

Water-quality assessment of the Lower Susquehanna River Basin, Pennsylvania and Maryland : sources, characteristics, anaylsis, and limitations of nutrient and suspended-seditment data, 1975-90 /

"National Water-Quality Assessment Program"

Advisory Committee on Federal Workforce Quality Assessment.

Mode of access: Internet.

Water-quality assessment of Francis E. Walter reservoir, Luzerne and Carbon Counties, Pennsylvania /

"June 1983."

Water-quality assessment of the Indiana Dunes National Lakeshore, 1973-74 /

Mode of access: Internet.

Water-quality assessment of White River between Lake Sequoyah and Beaver Reservoir, Washington County, Arkansas /

Mode of access: Internet.

Water-quality assessment of the Cypress Creek watershed, Warrick County, Indiana /

Mode of access: Internet.

Lake water quality assessment program : northeastern Illinois lakes /

"The Northeastern Illinois Planning Commission's Natural Resources Dept. conducted the lake assessment data collection effort for the six county northeastern Illinois region." -- P. iii.

Lake water quality assessment program, 1993 : northeastern Illinois lakes /

"January 1995."

Water quality assessment of Governor Bond (Greenville New) Lake Bond County, Illinois : 1977-1982.

"IEPA/WPC/84-011." -- Cover.

Methods for comparing water-quality conditions among National Water-Quality Assessment Study Units, 1992-1995 /

Mode of access: Internet.

Rainfall-runoff relationships and water-quality assessment of Coon Creek watershed, Anoka County, Minnesota /

Bibliography: p. 71-73.

No-reference image quality assessment in contourlet domain

The target of no-reference (NR) image quality assessment (IQA) is to establish a computational model to predict the visual quality of an image. The existing prominent method is based on natural scene statistics (NSS). It uses the joint and marginal distributions of wavelet coefficients for IQA. However, this method is only applicable to JPEG2000 compressed images. Since the wavelet transform fails to capture the directional information of images, an improved NSS model is established by contourlets. In this paper, the contourlet transform is utilized to NSS of images, and then the relationship of contourlet coefficients is represented by the joint distribution. The statistics of contourlet coefficients are applicable to indicate variation of image quality. In addition, an image-dependent threshold is adopted to reduce the effect of content to the statistical model. Finally, image quality can be evaluated by combining the extracted features in each subband nonlinearly. Our algorithm is trained and tested on the LIVE database II. Experimental results demonstrate that the proposed algorithm is superior to the conventional NSS model and can be applied to different distortions. © 2009 Elsevier B.V. All rights reserved.

Model and performance of a no-reference quality assessment metric for video streaming

Video streaming via Transmission Control Protocol (TCP) networks has become a popular and highly demanded service, but its quality assessment in both objective and subjective terms has not been properly addressed. In this paper, based on statistical analysis a full analytic model of a no-reference objective metric, namely pause intensity (PI), for video quality assessment is presented. The model characterizes the video playout buffer behavior in connection with the network performance (throughput) and the video playout rate. This allows for instant quality measurement and control without requiring a reference video. PI specifically addresses the need for assessing the quality issue in terms of the continuity in the playout of TCP streaming videos, which cannot be properly measured by other objective metrics such as peak signal-to-noise-ratio, structural similarity, and buffer underrun or pause frequency. The performance of the analytical model is rigidly verified by simulation results and subjective tests using a range of video clips. It is demonstrated that PI is closely correlated with viewers' opinion scores regardless of the vastly different composition of individual elements, such as pause duration and pause frequency which jointly constitute this new quality metric. It is also shown that the correlation performance of PI is consistent and content independent. © 2013 IEEE.

Quality assessment of video transmission in heterogeneous networks as applied to real-time telecare

This work looks into video quality assessment applied to the field of telecare and proposes an alternative metric to the more traditionally used PSNR based on the requirements of such an application. We show that the Pause Intensity metric introduced in [1] is also relevant and applicable to heterogeneous networks with a wireless last hop connected to a wired TCP backbone. We demonstrate through our emulation testbed that the impairments experienced in such a network architecture are dominated by continuity based impairments rather than artifacts, such as motion drift or blockiness. We also look into the implication of using Pause Intensity as a metric in terms of the overall video latency, which is potentially problematic should the video be sent and acted upon in real-time. We conclude that Pause Intensity may be used alongside the video characteristics which have been suggested as a measure of the overall video quality. © 2012 IEEE.