Picture Quality Analysis System

Features & Benefits

• Fast, Accurate, Repeatable, and Objective Picture Quality Measurement
• Predicts DMOS (Differential Mean Opinion Score) based on Human Vision System Model
• Picture Quality Measurements can be made on a Variety of HD Video Formats (1080i, 720p) and SD Video Formats (525i or 625i)
• Makes Picture Quality Comparison across Different Resolutions from HD to SD, or SD/HD to CIF
• User-configurable Viewing Condition and Display Models for Reference and Comparison
• Attention/Artifact Weighted Measurement
• Region Of Interest (ROI) on Measurement Execution and Review
• Automatic Temporal and Spatial Alignment
• Embedded Reference Decoder imported from MTS4EA
• Easy Regression Testing and Automation using XML Scripting with "Export/Import" File from GUI
• Multiple Results View Options
• Optional SD/HD SDI Interface with Simultaneous Generation/Capture, 2-channel Capture and 2-channel Generation with Swap-channel Capability
• IP Interface with Simultaneous Generation/Capture and 2-Ch Capture
• Cross Interface Configuration such as Generating from SDI and Capturing from IP or vice versa with Option SDI
• Preinstalled Sample Reference and Test Sequences

Applications

• CODEC Design, Optimization, and Verification
• Conformance Testing, Transmission Equipment, and System Evaluation
• Digital Video Mastering
• Video Compression Services
• Digital Consumer Product Development and Manufacturing

Picture Quality Analysis System

The PQA600 is the latest-generation Picture Quality Analyzer built on the Emmy Award winning Tektronix PQA200/300. Based on the concepts of the human vision system, the PQA600 provides a suite of repeatable, objective quality measurements that closely correspond with subjective human visual assessment. These measurements provide valuable information to engineers working to optimize video compression and recovery, and maintaining a level of common carrier and distribution transmission service to clients and viewers.

Compressed Video Requires New Test Methods

The true measure of any television system is viewer satisfaction. While the quality of analog and full-bandwidth digital video can be characterized indirectly by measuring the distortions of static test signals, compressed television systems pose a far more difficult challenge. Picture quality in a compressed system can change dynamically based on a combination of data rate, picture complexity, and the encoding algorithm employed. The static nature of test signals does not provide true characterization of picture quality.

Human viewer testing has been traditionally conducted as described in ITU-R Rec. BT.500-11. A test scene with natural content and motion is displayed in a tightly controlled environment, with human viewers expressing their opinion of picture quality to create a Differential Mean Opinion Score, or DMOS. Extensive testing using this method can be refined to yield a consistent subjective rating. However, this method of evaluating the capabilities of a compressed video system can be inefficient, taking several weeks to months to perform the experiments. This test methodology can be extremely expensive to complete, and often the results are not repeatable. Thus, subjective DMOS testing with human viewers is impractical for the CODEC design phase, and inefficient for ongoing operational quality evaluation. The PQA600 provides a fast, practical, repeatable, and objective measurement alternative to subjective DMOS evaluation of picture quality.

System Evaluation

User Interface of PQA600. Showing reference, test sequences, with difference map and statistical graph.

The PQA600 can be used for installation, verification, and troubleshooting of each block of the video system because it is video technology agnostic: any visible differences between video input and output from processing components in the system chain can be quantified and assessed for video quality degradation. Not only can CODEC technologies be assessed in a system, but any process that has potential for visible differences can also be assessed. For example, digital transmission errors, format conversion (i.e. 1080i to 480p in set-top box conversions), 3-2 pull-down, analog transmission degradation, data errors, slow display response times, frame rate reduction (for mobile transmission and videophone teleconferencing), and more can all be evaluated, separately or in any combination.

How It Works

The PQA600 takes two video files as inputs: a reference video sequence and a compressed, impaired, or processed version of the reference. First, the PQA600 performs a spatial and temporal alignment between the two sequences, without the need for a calibration stripe embedded within the video sequence. Then the PQA600 analyzes the quality of the test video, using measurements based on the human vision system and attention models, and then outputs quality measurements that are highly correlated with subjective assessments. The results include overall quality summary metrics, frame-by-frame measurement metrics, and an impairment map for each frame. The PQA600 also provides traditional picture quality measures such as PSNR (Peak Signal-to-Noise Ratio) as an industry benchmark impairment diagnosis tool for measuring typical video impairments and detecting artifacts.

Each reference video sequence and test clip can have different resolutions and frame rates. The PQA600 can provide picture quality measurement between HD vs SD, SD vs CIF, or any combination. This capability supports a variety of repurposing applications such as format conversion, DVD authoring, IP broadcasting, and semiconductor design. The PQA600 can also support measurement clips with long sequence duration, allowing a video clip to be quantified for picture quality through various conversion processes.

Prediction of Human Vision Perception

PQA600 measurements are developed from the human vision system model and additional algorithms have been added to improve upon the model used in the PQA200/300. This new extended technology allows legacy PQR measurements for SD while enabling predictions of subjective quality rating of video for a variety of video formats (HD, SD, CIF, etc.). It takes into consideration different display types used to view the video (for example, interlaced or progressive and CRT or LCD) and different viewing conditions (for example, room lighting and viewing distance).

Picture Quality Analysis System

A model of the human vision system has been developed to predict the response to light stimulus with respect to the following parameters:

• Contrast including Supra-threshold
• Mean Luminance
• Spatial Frequency
• Temporal Frequency
• Angular Extent
• Temporal Extent
• Surround
• Eccentricity
• Orientation
• Adaptation Effects

A: Modulation Sensitivity vs. Temporal Frequency


B: Modulation Sensitivity vs. Spatial Frequency

This model has been calibrated, over the appropriate combinations of ranges for these parameters, with reference stimulus-response data from vision science research. As a result of this calibration, the model provides a highly accurate prediction.

The graphs above are examples of scientific data regarding human vision characteristics used to calibrate the human vision system model in the PQA600. Graph (A) shows modulation sensitivity vs. temporal frequency, and graph (B) shows modulation sensitivity vs. spatial frequency. The use of over 1400 calibration points supports high-accuracy measurement results.

C: Reference Picture


D: Perceptual Contrast Map

Picture (C) is a single frame from the reference sequence of a moving sequence, and picture (D) is the perceptual contrast map calculated by the PQA600. The perceptual contrast map shows how the viewer perceives the reference sequence. The blurring on the background is caused by temporal masking due to camera panning and the black area around the jogger shows the masking effect due to the high contrast between the background and the jogger. The PQA600 creates the perceptual map for both reference and test sequences, then creates a perceptual difference map for use in making perceptually based, full-reference picture quality measurements.

Comparison of Predicted DMOS with PSNR

E: Reference 


F: Test


G: PSNR Map


H: Perceptual Difference Map for DMOS

In the example above, Reference (E) is a scene from one of the VClips library files. The image Test (F), has been passed through a compression system which has degraded the resultant image. In this case the background of the jogger in Test (F) is blurred compared to the Reference image (E). A PSNR measurement is made on the PQA600 of the difference between the Reference and Test clip and the highlighted white areas of PSNR Map (G) shows the areas of greatest difference between the original and degraded image. Another measurement is then made by the PQA600, this time using the Predicted DMOS algorithm and the resultant Perceptual Difference Map for DMOS (H) image is shown. Whiter regions in this Perceptual Contrast Difference map indicate greater perceptual contrast differences between the reference and test images. In creating the Perceptual Contrast Difference map, the PQA600 uses a human vision system model to determine the differences a viewer would perceive when watching the video.

The Predicted DMOS measurement uses the Perceptual Contrast Difference Map (H) to measure picture quality. This DMOS measurement would correctly recognize the viewers perceive the jogger as less degraded than the trees in the background. The PSNR measurement uses the difference map (G) and would incorrectly include differences that viewers do not see.

Attention Model

Attention Map Example: The jogger is highlighted

The PQA600, or PQASW Opt. ADV, also incorporates an Attention Model that predicts focus of attention. This model considers:

• Motion of Objects
• Skin Coloration (to identify people)
• Location
• Contrast
• Shape
• Size
• Viewer Distraction due to Noticeable Quality Artifacts

These attention parameters can be customized to give greater or less importance to each characteristic. This allows each measurement using an attention model to be user-configurable. The model is especially useful to evaluate the video process tuned to the specific application. For example, if the content is sports programming, the viewer is expected to have higher attention in limited regional areas of the scene. Highlighted areas within the attention image map will show the areas of the image drawing the eye's attention.

Artifact Detection

Artifact Detection Settings

Artifact Detection reports a variety of different changes to the edges of the image:

• Loss of Edges or Blurring
• Addition of Edges or Ringing/Mosquito Noise
• Rotation of Edges to Vertical and Horizontal or Edge Blockiness
• Loss of Edges within an Image Block or DC Blockiness

They work as weighting parameters for subjective and objective measurements with any combination. The results of these different measurement combinations can help to improve picture quality through the system.

For example, artifact detection can help answer questions such as: “Will the DMOS be improved with more de-blocking filtering?” or, “Should less prefiltering be used?”

If edge-blocking weighted DMOS is much greater than blurring-weighted DMOS, the edge-blocking is the dominant artifact, and perhaps more de-blocking filtering should be considered.

In some applications, it may be known that added edges, such as ringing and mosquito noise, are more objectionable than the other artifacts. These weightings can be customized by the user and configured for the application to reflect this viewer preference, thus improving DMOS prediction.

Likewise, PSNR can be measured with these artifact weightings to determine how much of the error contributing to the PSNR measurement comes from each artifact.

The Attention Model and Artifact Detection can also be used in conjunction with any combination of picture quality measurements. This allows, for example, evaluation of how much of a particular noticeable artifact will be seen where a viewer is most likely to look.

Comprehensive Picture Quality Analysis

The PQA600 provides Full Reference (FR) picture quality measurements that compare the luminance signal of reference and test videos. It also offers some No Reference (NR) measurements on the luminance signal of the test video only. Reduced Reference (RR) measurements can be made manually from differences in No Reference measurements. The suite of measurements includes:

• Critical Viewing (Human Vision System Model-based, Full Reference) Picture Quality
• Casual Viewing (Attention Weighted, Full Reference, or No Reference) Picture Quality
• Peak Signal-to-Noise Ratio (PSNR, Full Reference)
• Focus of Attention (Applied to both Full Reference and No Reference Measurements)
• Artifact Detection (Full Reference, except for DC Blockiness)
• DC Blockiness (Full Reference and No Reference)

Configure Measure Dialog


Edit Measure Dialog

The PQA600 supports these measurements through preset and user-defined combinations of display type, viewing conditions, human vision response (demographic), focus of attention, and artifact detection, in addition to the default ITU BT-500 conditions. The ability to configure measurement conditions helps CODEC designers evaluate design trade-offs as they optimize for different applications, and helps any user investigate how different viewing conditions affect picture quality measurement results. A user-defined measurement is created by modifying a preconfigured measurement or creating a new one, then saving and recalling the user-defined measurement from the Configure Measure dialog menu.

Easy-to-Use Interface

The PQA600 has two modes: Measurement and Review. The Measurement mode is used to execute the measurement selected in the Configure Dialog. During measurement execution, the summary data and map results are displayed on-screen and saved to the system hard disk. The Review mode is used to view previously saved summary results and maps created either with the measurement mode or XML script execution. The user can choose multiple results in this mode and compare each result side by side using the synchronous display in Tile mode. Comparing multiple results maps made with the different CODEC parameters and/or different measurement configurations enables easy investigation of the root cause of any difference.

Multiple Result Display

Integrated Graph

Resultant maps can be displayed synchronously with the reference and test video in a Summary, Six-tiled, or Overlaid display.

In Summary display, the user can see the multiple measurement graphs with a barchart along with the reference video, test video, and difference map during video playback. Summary measures of standard parameters and perceptual summation metrics for each frame and overall video sequence are provided.

Six-tiled display

In Six-tiled display, the user can display the 2 measurement results side by side. Each consists of a reference video, test video, and difference map to compare to each other.

Overlay display, Reference and Map

In Overlay display, the user can control the mixing ratio with the fader bar, enabling co-location of difference map, reference, and impairments in test videos.

Error logging and alarms are available to help users efficiently track down the cause of video quality problems.

All results, data, and graphs can be recalled to the display for examination.

Automatic Temporal/Spatial Alignment

Auto spatial alignment execution with spatial region of interest selected

The PQA600 supports automatic temporal and spatial alignment, as well as manual alignment.

The automatic spatial alignment with spatial region of interest in Measure mode selected independently of the spatial alignment function can measure the cropping, scale, and shift in each dimension, even across different resolutions and aspect ratios (for example, when aligning SD to HD video). If extra blanking is present within the standard active region, it is measured as cropping when this function is enabled.

The automatic spatial and temporal alignment allows picture quality measurement between reference and test videos of different resolutions and frame rates.

Region of Interest

Output Spatial ROI on Review mode for in-depth investigation

There are two types of spatial/temporal Region of Interest (ROI): Input and Output. Input ROIs are used to eliminate spatial or temporal regions from the measurement which are not of interest to the user. For example, Input Spatial ROI is used when running measurements for reference and test videos which have different aspect ratios. Input Temporal ROI, also known as temporal sync, is used to execute measurements just for selected frames and minimize the measurement execution time.

Output ROIs can be used to review precalculated measurement results for only a subregion or temporal duration. Output Spatial ROI is instantly selected by mouse operation and gives a score for just the selected spatial area. It's an effective way to investigate a specific spatial region in the difference map for certain impairments. Output Temporal ROI is set by marker operation on the graph and allows users to get a result for just a particular scene when the video stream has multiple scenes. It also allows users to provide a result without any influence from initial transients in the human vision model. Each parameter can be embedded in a measurement for the recursive operation.

Automated Testing with XML Scripting

Script Sample


Import/Export Script in Configure Measure Dialog


Result File Sample

In the CODEC debugging/optimizing process, the designer may want to repeat several measurement routines as CODEC parameters are revised. Automated regression testing using XML scripting can ease the restrictions of manual operation by allowing the user to write a series of measurement sequences within an XML script. The script file can be exported from or imported to the measurement configuration menu to create and manage the script files easily. Measurement results of the script operation can be viewed by using either the PQA600 user interface or any spreadsheet application that can read the created .csv file format as a summary. Multiple scripts can be executed simultaneously for faster measurement results.

SD/HD SDI Interface and IP Interface

SDI Generation / IP Capture

An SD/HD SDI interface and IP interface enable both generation and capture of SDI video and IP video with three modes of simultaneous operation.

Simultaneous generation and capture lets the user playout the reference video clips directly from the PQA600 into the device under test. The test output from the device can then be simultaneously captured by the PQA600. This saves the user from having to use an external video source to apply any required video input to the device under test. With this generation capability, files created by video editing software can be directly used as reference and test sequences for picture quality measurements.

2-channel SDI Capture

Simultaneous 2-channel capture lets the user capture two live signals to use as reference and test videos in evaluating the device under test in operation.

To accommodate equipment processing delay that may be present in the system, the user can use the Delay Start function when capturing video. Using Delayed Start minimizes the number of unused overhead frames in the test file and enables faster execution of the auto temporal alignment in the measurement.

2-channel SDI Generation

Simultaneous 2-channel generation capability, available only in SDI interface selection, supports two types of subjective testing. With two displays, the user can check the reference and test video content on side-by-side monitors.

Cross Interface Configuration

With one display and swap-channel capability, the user can check the reference and test video content without moving the eye's focus point. In any modes, the user can select the Cross Interface configuration such as generating from SDI and capturing from IP or vice versa. The compressed video file captured through IP will be converted to an uncompressed file internally by an embedded reference decoder imported from MTS4EA.

Supported File Formats for SD/HD SDI Interface

The SD/HD SDI video option can generate SDI video from files in the following formats (8 bit unless otherwise stated):

• .yuv (UYVY, YUY2)
• .v210 (10 bit, UYVY, 3 components in 32 bits)
• .rgb (BGR24)
• .avi (uncompressed, BGR32 (discard alpha channel) / BGR24 / UYVY / YUY2 / v210)
• .vcap (created by PQA600 SDI video capture)
• .vcap10 (10 bit, created by PQA600 video capture)

Option	Supported Frame Geometry	Formats Supported by SD/HD SDI Interface
SD-SDI	720×486, 720×576	525i/59.94, 625i/50
HD-SDI	1280×720, 1920×1080	720p/50, 720p/59.94, 720p/60
		1080i/50, 1080i/59.94, 1080i/60
		1080p/23.98, 1080p/23.98SF, 1080p/24, 1080p/24SF, 1080p/25, 1080p/29.97, 1080p/30

Supported File Formats for IP Interface

The IP interface option can generate and capture the compressed file in the following formats:

• .mpg
• .ts
• .trp

Supported File Formats for Measurement

All formats support 8 bit unless otherwise stated, and measurements use 8MSBs:

• .yuv (UYVY, YUY2, YUV4:4:4, YUV4:2:0_planar)
• .v210 (10 bit, UYVY, 3 components in 32 bits)
• .rgb (BGR24, GBR24)
• .avi (uncompressed, BGR32 (discard alpha channel) / BGR24 / UYVY / YUY2 / v210)
• ARIB ITE format (4:2:0 planar with 3 separate files (.yyy, .bbb, .rrr))
• .vcap (created by PQA600 SDI video capture)
• .vcap10 (10 bit, created by PQA600 video capture)

 

The following compressed files are internally converted to an uncompressed file before measurement execution:

 

Elementary Stream

• H.264/AVC/MPEG-4 Part 10 – Baseline, Extended, Main, High 10, High 4:2:2, and High 4:4:4 profiles all levels 1 to 5:1
• MPEG-2 – Main Profile at Main, High, and High 1440 levels, 4:2:2 Profile at Main and High Levels
• VC-1 – All Profiles, all Levels
• MPEG-4 Part 2 – Simple Profile at Levels 0-5 and Advanced Simple
• Profile at Levels 0-5
• H.263 Baseline

System Layer

Elementary streams contained within:

• MPEG-2 Transport/Program Stream
• MP4 Parts 1, 12, and 15
• ASF
• 3GPP
• DVD VOB
• Quicktime MOV

Preinstalled Video Sequences

Sequence	Resolution	Formats	Clips
Vclips	1920×1088	YUV4:2:0 planar	V031202_Eigth_Ave, V031255_TimeSquare, V031251_Stripy_jogger
	1920×1080	UYVY	V031251_Stripy_jogger
	1280×720	UYVY, YUV4:2:0 planar	V031002_Eigth_Ave, V031055_TimeSquare, V031051_Stripy_jogger with 3/10/26 Mb/s
	864×486	YUV4:2:0 planar	Converted V031051_Stripy_jogger with 2/4/7 Mb/s
	320×180	YUV4:2:0 planar	Converted V031051_Stripy_jogger with 1000/1780/2850 Kb/s
PQA300 without Trigger	720×486	UYVY	Ferris, Flower, Tennis, Cheer with 2 Mb/s_25 fps
	720×576	UYVY	Auto, BBC, Ski, Soccer
PQA300 with Trigger	720×486	UYVY	Mobile with 3/6/9 Mb/s
	720×576	UYVY	Mobile with 3/6/9 Mb/s

Performance You Can Count On

Depend on Tektronix to provide you with performance you can count on. In addition to industry-leading service and support, this product comes backed by a one-year warranty as standard.