In Broadcast - July 2015 - 44


44

www.inbroadcast.com | Vol: 5 - Issue 7 | July 2015

InMedia

Video Clarity's Log-Graphing
Tools Help Harness The Power
Of Full-Reference Testing
Adam Schadle, Vice President of Video Clarity, discusses the importance of log-graphing
tools and making the most of full-reference testing...

I

f you've read the past few articles
I have written for InBroadcast,
then you know that I've stressed the
importance of full-reference testing
when it comes to checking video and
audio quality. Full-reference testing is
one of the most accurate methods for
assessing quality changes.
The basic idea is to take a short
video clip, send it through a system
to be tested, and then compare the
output of the system to the original.
Any differences in any of the video
frames caused by the system can be
measured using a variety of objective
metrics in these side by side tests.
You get numerical results that very
closely approximate what a human
viewer would estimate the video
quality to be when watching the same
video sequences. In terms of time
and expense, full-reference testing
produces very accurate and highly
repeatable results at a much lower
cost than subjective video testing with
human viewers.
Broadcasting, cable, and IPTV
operators the world over rely on our
RTM real-time A/V monitors and
ClearView video quality analysers
to verify the quality of their output not only to ensure the effectiveness
of the delivery systems they have
in place now, but to determine the
best combinations of equipment and
delivery protocols to implement as the
industry evolves.
With
the
increasing
number
of variables, requirements, and
regulations involved in programme
delivery today, there are a lot of
measurements to track. So how can
you make sense of all of the data
from those full-reference tests? That's
where Video Clarity's log-graphing
tools come in, and they are included
with every RTM and ClearView
system. These tools take all the video
and audio quality test scores from
ClearView and RTM-generated log files
and plot the measurements on graphs,
so that users can clearly visualise

the performance of any device and
network path under test.
Video Clarity just released new and
improved versions of our formerly
Excel-based
log-graphing
tools.
You can see the data either as a
comparison of like tests or as a timebased interactive graph, with zooming
functions to track performance easily
over time. The new tools also let you
output the graphs in user-friendly PDF
format, which means you can associate
more volumes of test data with any
given group of measurement data sets.
One of the tools, the Metric Log
Grapher, applies to both ClearView
and RTM systems. This test-graphing
application automatically groups like
test-log files, such as DMOS, from a
system-generated log folder. The user
interface prompts for the folder that
contains the metric log files to be
processed.
Metric Log Grapher will process
all metric files with the following
suffixes: afreq, apeak, dmos, jnd, lkfs,
movie, peaq, psnr, ssim, and tpeak. It
automatically takes the data located in
the folder and creates a comparative
overlay graph of each metric type
on one or several graphs, depending
on how many different types of tests
are in the log folder. In this way,
groups of the same log-file type are
automatically overlaid together so
that you can compare the results of
each test that was done on a given
sequence or set of sequences. Metric
Log Grapher generates graphs and
consolidated comma separated value
(CSV) files that compare each video
component and audio channel. (If it
detects MS-SSIM -.ssim - in a DMOS
file, it will also create MS-SSIM graph
plots and CSV files.) It also generates
summary charts comparing minimums,
maximums, and averages. In the end,
users get a .ZIP folder containing PDF
files of the comparison and summary
graphs and their related CSV files,
which can be used to interpret the data
further.

Another tool, RTM Log
Grapher, applies only
to RTM products. This
software
application
creates a graph of
system-generated logs
that contain minimum,
maximum, and average
scores from an RTM
system's run-time tests.
With RTM Log Grapher,
you can take RTMgenerated test data of
any duration - hours,
days, or weeks - and
select all or part of the
data set to view using
interactive zoom and
scroll functions.
RTM Log Grapher has
an easy-to-use selection
map for each test type
that may be generated
in any given test run.
You can direct the RTM
Log Grapher to create
graphs for PSNR Y, Cr,
and Cb; DMOS Y; audio channels; LKFS;
audio alignment; and video offset for
both dynamic realignment and full
alignment.
Both Metric Log Grapher and RTM
Grapher are generally used on the
Video Clarity system that is running
the test, but you can also apply them
to ClearView or RTM test logs that have
been saved to any computer system

DMOS - Luma

PSNR Summary

running Windows.
Putting the data into graphic
form is an important way to spot
trends and errors, explain it to nontechnical audiences, and demonstrate
compliance. So however you're using
them, Video Clarity's log-graphing
tools help you visualise all of the data
in order to make the most of your fullreference testing.

Comparing LKFS from both inputs of the RTM System
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