Video Clarity Newsletter

Video Clarity created ClearView to aid in the assessment of Video Quality. ClearView provides many tools, which help broadcasters and manufacturers.

Broadcasters check their end-to-end solution during the buying phase, setup phase, and when anomalies are discovered. Manufacturers continually push the envelope in order to improve the video quality. ClearView provides a system solution for playing, recording, aligning, scoring, testing, and visually inspecting the video quality.

This newsletter will, generally, discuss inspecting, scoring and testing video quality on the left and show how ClearView can aid on the right. Several links provide additional reading material.

If you would like to schedule a demonstration or simply talk to us further, select Contact Us on the right side or visit us at one of our upcoming trade shows.

Multiple Side-by-Side Viewing Modes

The easiest way to judge video quality is to bring in a group of people and ask them. It sounds simple enough, but it is very time and resource consuming. Moreover, what does "good" mean? Do you put the original and processed videos on two different display? How do you calibrate the displays?

The Video Quality Expert Group (VQEG) created a specification for subjective video quality testing and submitted it to the governing body as ITU-R BT.500 Recommendation. This recommendation describes methods for subjective video quality analysis where a group of human testers analyze the video sequence and grade the picture quality. The grades are combined, correlated and reported as Mean Opinion Score (MOS).

The main idea can be summarized as follows:

• Choose video test sequences (known as SRC)
• Create a controlled test environment (known as HRC)
• Choose a test method (DSCQS SSCQE)
• Invite a sufficient number of human testers (20 or more)
• Carry out the testing
• Calculate the average score and scale

ClearView Solution

To aid in subjective testing, ClearView includes many valuable tools

• Record the incoming video from a variety of hardware interfaces and Input compressed and uncompressed files
  
• Play test sequences for any duration and rate
  
• Play test sequences side-by-side in multiple viewing modes or sent to 2 different displays
  
• View individual pixels, zoom, pan and scan, turn off fields, turn off colors, etc.

Quantitative Picture Analysis/Scoring

Objective Metrics build models that describe the influences of several physical image characteristics on video quality, usually through a set of video attributes thought to determine video quality. The models express video quality in terms of visible distortions, or artifacts introduced during the design process. Examples of typical distortions include flickering, blockiness, noisiness, or color shifts. The more sophisticated algorithms divide the image into layers to weight background and foreground differently.

VQEG and the University of Texas did extensive subjective testing and published their result. The objective models produce a score, and that score is mapped to the subjective results. VQEG and the University of Texas rated each algorithm on how well they did relative to the subjective testing.

To summarize, a quantitative objective score predicts subjective testing results.

ClearView Solution

To aid in objective scoring, ClearView includes many valuable tools

• Record, Input Your Test Sequence or Use a Pre-Loaded One
  
• Play the Test Sequence to the Device Under Test (DUT)
  
• Record the Output of the DUT or Input a File
  
• Automatic Temporal and Spatial Alignment
  
• Calculate the Score based on the Human Visual System - Sarnoff Algorithm
  
• Log & Graph the Score based on the JND Scale
  
• View the Video Sequences to See if You Agree

Pass/Fail Automated Testing

With the advent of Digital Television (DTV), video processing has changed significantly. Almost all videos are compressed, scaled, broadcasted or IP delivered, and decompressed. This has created an opportunity for video technology manufacturers.

Moreover, the average time to market from concept to delivery for high-tech equipment has shrunk from five or six years in the ‘90s to one or two years today. The first manufacturer to introduce a high quality product gains a sustainable competitive edge. As companies race to introduce more features in less time, the controlling factor for product introduction has shifted from the speed of development to the speed of validating that the system works.

To answer this demand, some testing organizations have adopted scripting in hopes of saving time. While running test scripts is faster than manual testing, how do you automate video quality analysis? Unfortunately, video quality testing has not kept up. Most companies employ testers with “golden eyes” to verify that the quality is acceptable. In addition, many talented testers prefer manual testing so that they can spend their time devising creative test cases rather than becoming proficient with complex scripting languages.

ClearView Solution

To aid in pass/fail testing, ClearView includes many valuable tools

• Record or Input Your "Gold" Sequence
  
• Record the Output of the Device Under Test (DUT) or Input a File
  
• -OR- Record the Output of the DUT and "Gold" Sequence Simultaneously
  
• Automatic Temporal and Spatial Alignment
  
• Calculate the Differences
  
• Log & Graph Pass/Fail against a Threshold
  
• Automated Scripting or Interactive GUI
  
• Optionally, Subjectively View the Video Sequences to Verify Pass/Fail