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The Objective Measurement Graph pane displays the graph of the DMOS, JND, PSNR, Spatial, or Temporal over time. The actual value, minimum, maximum and average values are displayed in the Objective Metric Controls pane. Examples, using the various objective measurements are on our website under www.videoclarity.com/WhitePapers/.

The Objective Metrics can be used to calculate the perceived video quality (Sarnoff/PQR JND, MS-SSIM DMOS), QC a product when the results are known (PSNR with Thresholding), looking for artifacts when no reference is present (Spatial and Temporal). In all cases, the metrics are displayed and written to a LOG file for off-line analysis.

DMOS

The MS-SSIM algorithm from the University of Texas is used as a basis for a top-down way of predicting the video quality. This is a full reference algorithm as it measures the perceived structural similarity between the original and processed videos. It then correlated this data to the DMOS scale using the LIVE database at the University. The DMOS scale is between 0 and DMOS Max Value (4, 7, or 10 based in the ClearView Configuration Menu); where 0 is perfect. For more information about MS-SSIM or the DMOS scale, please refer to our website at www.videoclarity.com/WhitePapers/.

JND

The Sarnoff/PQR JND model is a method of predicting the subjective rating of a group of human testers using a bottom-up approach. It looks for blocks, blurring, luminous variations, noise, etc. artifacts and generates a number based on the weighted sum of these artifacts. It then correlates this number to the JND scale using the VQEG database. The JND is theoretically between 0 and 100; where 0 is perfect. In practice, the number should never exceed about 13 or 14. For more information about the Sarnoff algorithm or the JND scale, please refer to our website at www.videoclarity.com/WhitePapers/a>.

PSNR

The PSNR algorithm measures the video differences between the original and the processed video in absolute terms. This is termed an objective metric as it does not talk about perceived quality to the human eyes. It measures the absolute differences using the following algorithm.

PSNREquation1

The PSNR is given in decibel units (dB), which measure the ratio of the peak signal and the difference between two images. An increase of 20 dB corresponds to a ten-fold decrease in the RMS (root mean squared) difference between two images. For simplicity, we display 100 when the images are identical. The actual value is infinite.

PSNR measures all of the differences between the reference and processed videos. It does not try to weight these. The calculation is very fast and is used to perform QA/QC when the perceived video quality is already known.

Spatial

Spatial measures the activity within a video sequence. Spatial is a no-reference metric. Large values indicate a substantial change within an image – for example: panning stadium crowds would generate a large Spatial Index. A solid color would produce a low Spatial Index. For more information about the Spatial metric, please refer to ITU-T P.910 (a link is on our website at www.videoclarity.com/WhitePapers/).

SpatialEquation

The Spatial Index is the STD deviation, and presented in Pixel Value units, which measure the value difference from one pixel to its neighbors across the image. If two sequences are being played, then the Spatial Index is calculated for both video sequences, and the differences are displayed and graphed. The Log file holds the actual values for both video sequences and the differences.

Temporal

Temporal measures the activity frame-to-frame within a video sequence. Temporal is a no-reference metric. Large values indicate a substantial change occurred during the video sequence – for example: a scene change would generate a large Temporal Index. A frozen frame would generate a Temporal Index of 0. For more information about the Temporal metric, please refer to ITU-T P.910 (a link is on our website at www.videoclarity.com/WhitePapers/).

TemporalEquation

The Temporal Index is the STD deviation, and presented in Pixel Value units, which measure the value difference from one pixel across many frames. If two sequences are being played, then the Temporal Index is calculated for both video sequences, and the differences are displayed and graphed. The Log file holds the actual values for both video sequences and the differences.

Objective Measurement Graph
PSNR_Graph

The Objective measurement graph is enabled by pressing the Graph button in the Objective Metric Controls pane. If all of the data has already been collected (which it does by playing through the 2 video sequences the first time after the Objective Metric is turned on), the graph will be displayed as shown above. If the data has not been collected, the Graph button will switch to Graphing mode, and a horizontal line will be drawn across the center of the screen. The video sequences are played from the start through the end points. To change the start and end points, use Clip Alignment to adjust the first and last positions for both Viewports. Once the video sequences have been played, the graph is scaled and the minimum, maximum, and average Objective Metrics are displayed along with the graph. Using the shuttle bar (slide bar), the user can display any frame to visually assess the 2 video sequences.
Note: The frame is associated with the right side of the slide bar.

Pixel Values

To display individual pixel values press the right mouse button.

Note: the left mouse button will still control panning.

Scrolling to any X,Y location will show the pixel values for the same location for both video sequences. Holding the right button while moving the cursor will allow moving the cursor in increments of 4 pixels at a time.

Note 2: to get finer control of the X,Y location, use the Pixel Value Hotkeys, which increment in 1-pixel increments, or type in an X,Y location in the Pixel Value Controls
Note 3: you can also type in an X,Y location directly.

Objective Metric Controls

The Objective Metric Control Pane controls the behavior of the JND, PSNR, Spatial, and Temporal objective metric, displays the Pixel Values at a chosen location, and sets the A-B parameters.

Objective Metrics Controls
PSNRPane

JNDPane

DMOSPane

Objective Metrics Description

DMOS This tab selects the DMOS Metric settings
Note: Moving among the Objective Metrics does not turn on or off the metric calculations. This simply displays the collect data.
Note2: DMOS takes a considerable amount of time so we do not allow moving to another pane while this calculation is processing.
JND This tab selects the JND Metric settings
Note: Moving among the Objective Metrics does not turn on or off the metric calculations. This simply displays the collect data.
Note2: JND takes a considerable amount of time so we do not allow moving to another pane while this calculation is processing.
PSNR This tab selects the PSNR Metric settings
Note: Moving among the Objective Metrics does not turn on or off the metric calculations. This simply displays the collected data.
Spatial This tab selects the Spatial Metric settings
Note: Moving among the Objective Metrics does not turn on or off the metric calculations. This simply displays the collected data.
Note2: If you have 2 video sequences loaded, it will calculate the Spatial for both sequences independently and subtract the difference. The Log file will have 3 sets of data. The Graph will display the subtracted difference.
Temporal This tab selects the Temporal Metric settings
Note: Moving among the Objective Metrics does not turn on or off the metric calculations. This simply displays the collected data.
Note2: If you have 2 video sequences loaded, it will calculate the Temporal for both sequences independently and subtract the difference. The Log file will have 3 sets of data. The Graph will display the subtracted difference.
PixVal This tab enables you to view individual Pixel Values. Please refer to thePixel Value Controls for more information.
A Minus B This tab enables you to set the A-B parameters. Please refer to the A-B Controls for more information
On This enables/disables calculating the Objective Metrics. When checked, the Metric calculation is enabled. Data is collected while the sequence is playing. To play the sequence, please press the Graph or Log buttons. When Unchecked, the calculated data is removed from memory.
Note: Unchecking the box will stop an already activated objective calculation.
Spatial Selecting this applies the spatial alignment calculated in the Metric Adjust pane.
Norm/Normalize Selecting this applies the color hue/luminance intensity offset calculated in the Metric Adjust pane.
Thrs This allows a threshold to be set of Y, Cb and Cr. Each component can be turned on/of. PSNR values under this threshold are returned as failures (including Luminance and Chrominance). JND, Spatial, and Temporal values over this threshold are returned as failures.
Note: JND, DMOS combine Cb & Cr together so there is only 1 threshold for color.
Failures These are informational messages and cannot be changed. It displays the number of frames (or fields) that are outside the threshold (see not above).
Y/G Show the Objective Metric data for the Y/G value
Cb/B Show the Objective Metric data for the Cb/B value
Cr/R Show the Objective Metric data for the Cr/R value
F1/Fr, F2, Current, min, max, avg These are informational messages and cannot be changed.
Current – the current metric value
F1/Fr – the current Sarnoff JND or DMOS metric value for Field #1 or Frame
F2 – the current Sarnoff JND or DMOS metric value for Field#2
Min – the minimum metric value
Max – the maximum metric value
Avg – the average as defined in the appropriate ANSI spec. For PSNR the average is based on T1.TR.74-2001; for DMOS and JND, average is a 4th squared, 4th root minkowski average; for Spatial, Temporal it is a straight average.
Graph Display the Y/G, Cb/B, or Cr/R values over time on the Objective Metric Graph.
If the data has not been calculated, then pushing this button will play the video sequences, calculate the Objective Metrics, and display them. Note 1: Y/G data will be printed in Green. Cb/B data will be printed in Blue. Cr/R data will be printed in Red.
Note 2: In the upper, right corner, the graph will display D for DMOS, J for JND, P for PSNR, S for SPATIAL, and T for TEMPORAL.
Log This creates a log file which includes:

  • Video Sequence Library
  • Video Sequence Name
  • Clip Alignment Parameters
  • Objective Metrics
    • DMOS
    • JND
    • PSNR
    • SPATIAL
    • TEMPORAL

If the data has not been calculated, then pushing this button will play the video sequences, calculate the Objective Metrics, and write them to the appropriate file.
When you press log, you will be prompted to enter a location to save the file along with a filename.

Note 1: You can restore these files using File Import, and ClearView will automatically load the clips, restore the image format, video format, alignment, and read in the Objective Metrics.
Note 2: Files are written as a 12 column, space-delimitated file. 

  • The first 3 columns are Viewport A’s data.
  • The second 3 columns are Viewport B’s data.
  • The third  3 columns are Viewport B’s data subtracted from Viewport A’s data 
  • The fourth 3 columns are the results against the threshold (aka pass/fail)


Pixel Value Controls
PixelValuePane

Pixel Value Descriptions

Y/G Cb/B Cr/R A B These are the pixel values in decimal at the same X,Y location for video sequence A & B.The color is also displayed for reference.Note 1: if you zoom the original image, then you can see the cursor more clearly.
Note 2: to get finer control of the X,Y location, use the Pixel Value Hotkeys, which increment in 1-pixel increments, or type in an X,Y location in the Pixel Value Controls.
X, Y This is the X, Y location of the current pixel.Pressing the right mouse button enables this mode.Note: This is referenced within the original image – not the location after the video sequences have been rendered.

A Minus B Controls
A-BPane

A Minus B Descriptions

A-B Use Diff Threshold Checking this box performs a |A-B| > Threshold on either the Chroma or Y pixels
Unchecking this box, performs an A-B > 0 on all pixel values
If true, it displays the difference.
If false, it displays black
Threshold This is the threshold value for the A-B Use Diff Threshold above
Chroma Check means that the A-B calculation will be performed only on the chroma values (Cr & Cb)
Uncheck means that the A-B calculation will be performed only on the luminance value (Y)
A-B Addback Checking this box performs a |A-B| > Threshold calculation.

  • If (A-B) >= Threshold, a Green pixel is displayed
  • If (B-A) >= Threshold, a Yellow pixel is displayed
  • If (((A-B) < Threshold) && ((B-A) < Threshold)), the original video sequence is displayed

Unchecking this box displays the results of |A-B| if it is greater than the threshold.

Metric Adjust Controls
MetricAdjust

Metric Adjust Descriptions

Spatial-Align Checking this box performs a Spatial Alignment in both the horizontal and vertical direction. The current video frame in Viewport B is compared to the current frame in Viewport A. The results are shown in X, Y.
Note: The video sequence can be adjusted on the fly based on a setting in configure. This offset only applies to the objective metrics.
X, Y These are the X,Y offset values after the Spatial-Alignment. They can be overridden.
Note 1: the offsets are restricted to be +/- 8 (X) and +/- 16 (Y).
Note 2: the X offset is restricted to divisible by 2 because the color is 4:2:2.
Note 3: the Y Offset is restricted to divisible by 2 for interlaced content.
Normalize Checking this box performs a Luminance Intensity and Chrominance Hue calculation. The current video frame in Viewport B is compared to the current frame in Viewport A. The results are show in Y/G, Cb/B, Cr/R.
Note 1: The video sequence is not adjusted. This offset only applies to the objective metrics.
Note 2: The offset is a linear offset per frame and is used to make PSNR more robust.
Y/G, Cb/B, Cr/R These are the Y/G, Cb/B, and Cr/R luminance/chrominance offsets after the Normalization.
X, Y, W, H This allows you to set a window size for the objective metrics. By default it is full screen, but the size can be adjusted.
Note: to remove borders with noise, this tool can be used to exclude the noise.
 
 
 
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