Inter BEE 2010 Report: Digital Broadcasting Puts AV Data Quality and Image Testing Gear in Spotlight.
Noticeable at Inter BEE 2010 was the proliferation of AV data quality testing equipment. Quality evaluation technologies have never stood out as much as they have been recently. These technologies and software applications are suddenly popping up everywhere.
Devices that measure the quality of radio waves have always been around, but devices specialized to measure digital data and the picture quality of that data have been thin on the ground. The advances in quality control promise to reduce the incidence of reception trouble. (Koji Suginuma)
The Difference between Quality and Picture Quality
Devices that evaluate quality of the AV stream have been offered by a limited number of manufacturers in the past, but at this year's exhibition you could feel the expansion in this area.
A lot of the exhibits featured quality evaluation equipment. Quality evaluation and picture quality evaluation are often confused, and so it is important to know the difference between these two completely different things.
Quality evaluation involves assessing whether AV data for digital broadcast adheres to the "syntax" rules for the data. Japanese television broadcasting uses MPEG2 to encode content, but before verification can be assessed, the placement of data must be inspected for correctness.
Audiovisual data encoded with MPEG2 is multiplexed into the data string. Audio and visual data is not placed into separate radio waves or data streams, rather they share the same single stream. This sharing process is called multiplexing. Conversely, the process of sorting out the audio and visual components into their original form is called demultiplexing. For demultiplexing to be successful, multiplexing must follow syntax rules.
Including many different programs in a single broadcast wave is also the job of multiplexing. With terrestrial digital broadcasting, a single frequency (broadcast station) is not limited to one HDTV program broadcast. HD can be mixed with SD, or multiple SD programs can be transmitted together in an SD-only broadcast.
Furthermore, viewers can select up to 3 viewing angles from within the broadcast program video. All of this is possible through multiplexing, with indespensible syntax checking performed by quality evaluation devices and software.
Once the validity of the multiplexed data has been confirmed, the audiovisual data has to be checked to ensure that it has been correctly encoded. If video data is not correctly assembled, it might cause the screen at the receiving end to freeze, or go completely black.
These phenomena are easy to see when they happen, but without inspecting the data it's impossible to tell whether their occurrence is an intended effect or a malfunction due to an encoding problem. Quality evaluation devices also provide these kinds of alert.
Picture Quality Evaluation -- An Alternative Subjectivity
In contrast, picture quality evaluation shows how faithful an image is when compared with its original. Picture quality does not indicate some level of beauty. Picture quality evaluation devices do not give evaluations like "gorgeous colors" or "crisp image". Rather, there are internationally standardized methods such as ISO that are used to assess picture quality. Once a video has been encoded and decoded, it is compared with its original to determine how much it has been degraded by the process.
To make this measurement, a number of evaluators must look at the video over and over again. This requires a specialized evaluation room adjusted for brightness and background according to the international standards. Obviously, since this kind of highly involved picture quality evaluation can almost never be carried out in practice, picture quality evaluation devices have appeared to do the job.
Picture quality evaluation devices do not only indicate differences compared to the original image. There are also systems that include visual modeling so that the device can determine whether those differences will have a big effect on viewers or not. Users of these devices must have some level of knowledge since picture quality evaluation will be affected depending on the type of visual model used.
Responding to MVC
Nikon has added the NH264H1 (OPH3) as a 3-D video content option for its H.264 analysis tools. This system inspects the 3-D format MVC stream.
MVC is designed to expand MPEG 4 AVC/H.264 (AVC/H.264 hereafter), so it's easy to understand why the company is providing this additional option to their H.264 analysis tools. This technology will be used for authoring 3-D Blu-ray discs and so on.
Evaluation by Guessing the Original Image
The MP Factory Ver.5 from KDDI R&D labs inspects AV data in the stream or in storage, and supports MPEG 1/2/4 AVC/H.264. This system is mainly designed for quality testing, but is also capable of picture quality testing.
The software features functions that indicate the PSNR value (how much difference compared to the original), without actually using the original image to perform the picture quality testing. KDDI says the software can guess the original image from the data in the stream after encoding and offers highly accurate estimations about the differences of the image being inspected.
MP factory is available function by function, in kit form that users can assemble as software they develop themselves. So, rather than as stand-alone software for testing, it includes those products that are sold as the functions mentioned above.
Support for a Variety of Tests
K-WILL, a specialist testing equipment manufacturer exhibited the company's VP3000H quality testing equipment with SDI input. The VP3000H features a mode for detecting digital noise and freezes by comparing the original signal, and intermittent audio, and a mode that detects block distortion, freezes and intermittent audio without using the original signal. The VP3000H uses a multi-window LCD to display a variety of information simultaneously and enable the user to thoroughly check the state of the object being tested.
K-WILL also presented a reference exhibit of their MPEG PROBE testing device with IP packet input. This technology has been designed for content streamed using IP packets, and can simultaneously test multiple packets. The company plans to develop systems to deal with both SDI input and IP input in the near future.
Encoders used for development
Interra Systems exhibited their file-based content verification quality testing tool, Baton. The testing engine that lies at the heart of Baton has been used by encoder makers all over the world for testing during encoder development for many years.
Digital encoding involves a wide variety of guidelines, to which signals must conform. However, quite often there are holes in the guidelines, or unidentifiable sections remain, and sometimes conflicting demands arise between different guidelines. In the Japanese system, there are standard guidelines and operational guidelines, and general equipment must be compliant with these operational guidelines. To date, Baton has been used to develop testing engines once the complex guidelines have been understood, but is now available as a generic testing tool.
IT Access is the agent selling this product in Japan.
Flagship Picture Quality Evaluation Devices
The Clear View Series developed by an American company Video Clarity was exhibited exclusively by Techno House. This series is mostly storage-type picture quality testing equipment. Using two types of visual models to indicate picture quality, both the original image and the image to be tested are recorded in the device, which calculates the PSNR value indicating differences.
Users need to understand the particular characteristics of the visual models to use this system. This device is used for equipment development as well as other uses such as assessing new encoders bought by terrestrial TV networks in the US etc. The series also features devices capable of real-time monitoring, which enable the user to monitor PSNR changes and observe transmission quality and so forth.
There was a lot of this type of quality testing equipment on display at Inter BEE. Up until now broadcasting has been the only actual source of terrestrial digital transmission, but in future, these sources will come from a variety of devices such as in-house broadcasting modulation equipment. Quality testing devices will be indispensable tools in determining causes as to why images do not appear on connected TV sets and so forth.
Photo 1 Nikon exhibited their 3-D MVC data inspection tools.
Photo 2 K-WILL's SDI-connectable VP3000H reads digital AV data and performs quality tests.
Photo 3 The Clear View by America's Video Clarity uses visual models to assess picture quality, and is also used to test encoders.
Photo 4 The Clear View by America's Video Clarity Series internally records the original image and image to be tested.