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How to quickly measure the system performance of high-definition images with image quality analyzer

The purpose of HD (high definition) TV system is to create a new quality experience (QoE). This QoE is determined by several factors, the most important of which is image and sound quality. There is an inverse relationship between quality and content. When the quality is the same, the content becomes the key to determine the quality of the program, and when the content is the same, the quality becomes the decisive factor. In any case, TV is always a business behavior, and every operator must determine a strategy to balance the contradiction between content and quality

the purpose of testing and measurement is nothing more than to improve and manage the quality of programs. Similar to the automobile industry, we must accept the fact that quality control is not a process of patching up in the later stage of program production, but must be started from the beginning and implemented in every link of the program production process

although the analog signal and full bandwidth digital visual tool geometry and material have a significant impact on the machined surface, chip composition, cutting force and tool wear, the quality of frequency can be indirectly characterized by measuring the distortion of static test signal, but the compression TV system faces more arduous challenges. The image quality in a compression system may change dynamically with the data rate, image complexity and the coding algorithm used. The static nature of the test signal cannot reflect the real characteristics of image quality. At this time, we can use the test scene with normal content and moving images to measure the signal quality, and determine the measurement results according to the audience's report, but this method of evaluating the performance of compressed video system is inefficient. The image quality analyzer pqa500 of Tech provides a fast, practical, repeatable and objective measurement scheme for the subjective evaluation of image quality

pqa500 introduction

pqa500 input is two video files: an original reference video sequence file and a compressed or processed damaged reference file. First, pqa500 can align the two input sequences in space and time without the embedded calibration stripes in the video sequence, then analyze the quality of the test video according to the human visual system and attention model, and output a quality measurement result highly related to subjective evaluation, including the overall quality report of the input video, the frame by frame measurement result and the damage map of each frame image. In addition, pqa500 also provides traditional image quality measurement data such as PSNR (peak signal-to-noise ratio) as industry benchmarks, as well as image damage diagnosis toolkit for measuring typical video damage and detecting image defects

Figure 1: pqa500 image quality analysis card and MTM 400 MPEG transmission data stream monitoring of Tektronix

each reference video sequence and test clip has different resolution and frame rate. Pqa500 can measure the image quality between HD and SD, between SD and CIF, and in many other combinations. Pqa500 also supports time unlimited measurement videos, allowing quantitative testing of the image quality of the whole film through various conversion technologies

smpte 372m standard

in order to obtain the best quality video materials, 1080p50 or 1080p60 format has become the best choice. Since these two formats require RGB 4:4:4 processing in post production, a high-speed interface is required to process additional data. At present, most devices rely on dual links to realize this high-speed interface, but SMPTE 372m dual link standard supports multiple modes and color space when transmitting video and audio data. To provide first-class measurement results, we must carry out single channel analysis, inter channel timing measurement, and provide combined waveforms and vectors for color grading applications. Tektronix's wfm/wvr7120 modular waveform monitoring product series can provide detailed analysis for such applications, and its accuracy is enough to carry out reliable physical layer measurement at 1.5gbit/s

lip synchronization problem

the most annoying quality damage in TV signals is the asynchrony of audio and video. This kind of problem is called lip synchronization problem in the industry. This problem occurs when there is a time difference between audio processing and video processing, and the two are not aligned correctly

some people in the industry have tried to use but constantly move and apply, and clamp the shockproof rubber pad between the indenter base and the sample table; For long-distance transportation, the original packaging should be restored to the sample. The heaviest force will make them destroy the test and correction methods to solve this problem, but most coding schemes actually cut off the auxiliary data field, and the traditional test signal is located in this auxiliary data field. With the increasing popularity of multi-channel audio and compressed surround sound audio, it becomes more difficult to solve this problem

therefore, using a specific set of audio and video programs for offline testing is still one of the optional methods. Although the test mode adopted by most signals needs to rely on the operator's hearing and vision to find the correct timing relationship between audio and video, the award-winning test program provided by Tektronix is now integrated not only in the high-end analyzer, but also in the new wfm7120

when using this test program, first send a group of relevant audio and video test signals to the system, and then the waveform monitor will accurately measure the timing difference between this group of audio and video. The test signal supports SD and HD digital formats

cross layer monitoring

whether HDTV can achieve commercial success depends on whether it can provide viewers with the best image quality. The leading standard in satellite and cable TV applications is h.264/mpeg-4 Part 10, while vc-1 and H.264 dominate in the field of IP

in order to make full use of all the potential benefits of these video codecs, we must correctly debug the signal transmission channel, whether it is satellite transmission, wired transmission, ground transmission or IP transmission. Low resolution formats such as CIF or QCIF are used in mobile TV, but the problems are very similar to IP channels. For traditional satellite TV, cable TV or terrestrial radio and television systems, the injection frequency domain and video domain must be turned off at the same time

this method is called cross layer monitoring. It is a preprocessing method, which can quickly isolate faults and identify the root causes of faults when encountering transmission problems. In order to achieve economies of scale, Tektronix has introduced the RF channel rotation detection mechanism into its instruments, which can carry out intelligent circular detection between various channels, while still giving priority to the channels with high attention or high value. In the IP domain, rapid monitoring across many segments can now be achieved, which can immediately indicate important signal faults and make in-depth diagnosis, so as to help designers correctly find the problem

mtm400 MPEG, RF and IP monitors ensure that service quality requirements and subsequent R & D resources are tracked and met for product development and verification

basic data flow analysis

in order to improve the quality of H.264, tech has also developed a test suite for basic data flow analysis to improve programming efficiency. The kit includes an H.264 multiplexer, a cache analyzer, and a transport stream analyzer. Among them, the H.264 multiplexer can help users create test transmission streams by using the vclips test data stream Library of Tech. the buffer analyzer is used to verify the consistency of set-top box design and data streams, and the transmission stream analyzer is used to ensure that the data streams transmitted are h.264 encoded data streams

the test suite can conduct real-time measurement together with mt430 and other test hardware. In order to improve connectivity and cross layer testing functions, the upgraded mt430 has a variety of RF and IP interfaces

to support end-to-end testing of HDTV requires various testing tools and expertise in different domains, such as uncompressed multi format video and audio, compressed video for playback, and file video required for storage and workflow

Author: Winfried schultz

tektronix video instrument marketing manager

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