Digital Video Measurements
- Updated2023-08-17
- 16 minute(s) read
Digital Video Measurements
If you are used to analog component measurements, you will find that digital video measurements are closely related to the analog component measurements. One important reason is that digital video signals are component signals by nature. Secondly, NI VMS analyzes digitized analog signals and digital signals by means of the same software tools. Conveniently, this gives digital video analysis the same familiar look and feel as analog analysis in NI VMS.
Time Required for NI VMS Measurements
Test time for digital signals tends to be longer than for CAV signals because digital video usually has higher resolutions and because NI VMS must test three channels rather than one for most digital video parameters. Longer testing times are to a certain extent countered by the fact that digital requires NI VMS to test fewer parameters because of the lower complexity of the signals themselves.
NI VMS Measurements
The digital video measurements do not match the analog component video measurements exactly. Some of the analog component measurements are not relevant to digital video and have been omitted from the list of digital measurements. Of the measurements that are common to analog and digital, you will find that a few digital measurements differ slightly. This is due to specific conditions that apply differently to analog and digital video. The digital video measurements include:
- Channel Delay
- Colour Bars
- Edge Finder
- Group Delay
- Horizontal Timing
- K Factor
- Level Meter
- Line Frequency
- Multiburst
- Noise Spectrum
- Non-Linearity
- Short-Time Distortion
- Sweep
- Video Signal Info
These measurements are described in the following:
Channel Delay
Pattern(s): Multiburst or Sweep
Definition: This is a measurement of the relative timing of the three component video channels. The measurement analyses the time (phase) difference between pairs of channels using a test pattern containing identical sinusoidal signals in all channels - the third burst of a multiburst, or the center of a sweep. A negative delay from channel A to B indicates that channel A leads channel B.
Colour Bars
Pattern(s): 75% or 100% Colour Bars
Definition: This is a measurement of the amplitude of 8 color bars (white, yellow, cyan, green, magenta, red, blue, black) in a single specified component channel. Colour bar levels should be measured for each component to verify the brightness, contrast, and color fidelity of the video signal. They can also be used as a basic indication of non-linear distortions. Nominal levels can be predicted for each color and component and an error value calculated from the measured levels. There are 24 measurements for each color component type (sRGB, StudioRGB or YCbCr). Refer to relevant standards for colourimetry equations. Note that SDTV and HDTV use different equations. 100% color bars are normally used as the test signal because they use the full dynamic range of all component channels.
| Measurement | Definition |
|---|---|
| Bar Amplitude | Amplitude of the color bar measured over its center |
| Bar Amplitude Error | The difference between the measured color bar amplitude and its nominal amplitude, expressed as a percentage of full range at the given resolution (number of bits) and given color coding sRGB, StudioRGB or YCbCr. |
The following table lists nominal bar levels for 100% color bars at 8 bit resolution.
| 576p, 480p (SDTV,EDTV) | 720p, 1080i (HDTV) | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Colour | G | B | R | Y | Cb | Cr | Y | Cb | Cr |
| White | 255 | 255 | 255 | 255.0 | 0.0 | 0.0 | 255.0 | 0.0 | 0.0 |
| Yellow | 255 | 0 | 255 | 225.9 | -127.4 | 20.7 | 236.6 | -127.5 | 11.7 |
| Cyan | 255 | 255 | 0 | 178.8 | 43 | -127.5 | 200.8 | 29.2 | -127.5 |
| Green | 255 | 0 | 0 | 149.7 | -84.4 | -106.7 | 182.4 | -98.3 | -115.8 |
| Magenta | 0 | 255 | 255 | 105.3 | 84.4 | 106.7 | 76.2 | 98.3 | 115.8 |
| Red | 0 | 0 | 255 | 76.2 | -43.0 | 127.5 | 54.2 | -29.2 | 127.5 |
| Blue | 0 | 255 | 0 | 29.1 | 127.4 | -20.7 | 18.4 | 127.5 | -11.7 |
| Black | 0 | 0 | 0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
Edge Finder
Pattern(s): Any signal containing one or more waveform edges or bars
Definition: This is a measurement of the amplitude and timing of some or all the waveform edges or bars located over the specified search interval(s). A bar is classified as a rising edge followed by a falling edge. You can configure multiple measurements over multiple video lines.
You can configure the maximum numbers of found edges or bars, as well as the Low ref and high ref levels. If multiple edges or bars are found, they will be reported in separate index numbers in the results list.
The following table includes descriptions of the UI controls for the edge finder.
| Measurement Control | Description |
|---|---|
| Operation | Specifies the measurement type. |
| Max Edges | Specifies the maximum number of edges to find. |
| Operations parameters [Index] | Specifies the number of measurements to configure. You can define the following parameters for each measurement:
|
| Remove | Removes the current indexed measurement in Operations parameters. |
| Empty | Deletes all of the configured measurements in Operations parameters. |
| BC | Enables backward-compatible reporting of measurements. |
| Low ref level | Specifies the low ref level of the measurement. |
| High ref level | Specifies the high ref level of the measurement. |
| Channel Selection | Specifies which color component channels to include in the measurement. Contains the following options:
|
| Items to measure | Specifies which values to measure. Contains the following options:
|
The following table includes descriptions of the returned results for the edge finder.
| Measurement | Definition |
|---|---|
| Measurement Type | Indicates the type of measurement used, including rising edges, falling edges, or bar. |
| Max Edges | Indicates the maximum number of edges to find, as configured in the UI, where -1 indicates all edges. |
| Low Ref Level | Indicates the low reference level, as configured in the UI. |
| High Ref Level | Indicates the high reference level, as configured in the UI. |
| Color Coding | Indicates the type of color coding used, where 1 indicates RGB and 0 indicates YCbCr. |
| Frame Index | Indicates the frame number on which the measurement was executed. This measurement is included in the operation parameters index. |
| Line | Indicates the line number of the measured frame. This measurement is included in the operation parameters index. |
| Search Start | Specifies the start time, in microseconds, on the specified line of the analysis area. This measurement is included in the operation parameters index. |
| Search End | Indicates the end time, in microseconds, on the specified line of the analysis area. This measurement is included in the operation parameters index. |
| Number of “m” “c” | Indicates the number of "m" and "c" found, where, "m" indicates rising edges, falling edges, or bar, and "c" indicates the color component. This measurement is included in the operation parameters index. |
| Low Level | Indicates the level of the signal at the bottom of the edge or bar. This measurement can only be used when you specify Rising Edges or Falling Edges as the measurement type. |
| High Level | Indicates the level of the signal at the top of the edge or bar. This measurement can only be used when you specify Rising Edges or Falling Edges as the measurement type. |
| Amplitude Level | Indicates the difference in amplitude between the low level and the high level. This measurement can only be used when you specify Rising Edges or Falling Edges as the measurement type. |
| Rise Time | Indicates the time between the configured Low Ref (%) and High Ref (%) amplitude levels of a rising edge. This measurement can only be used when you specify Rising Edges or Bar as the measurement type. |
| Fall Time | Indicates the time between the configured High Ref (%) and Low Ref (%) amplitude levels of a falling edge. This measurement can only be used when you specify Falling Edges or Bar as the measurement type. |
| Center | Indicates the time of the 50% amplitude level of an edge transition, or the center of a bar. This measurement can only be used when you specify Rising Edges, Falling Edges, or Bar as the measurement type. |
| Width | Indicates the width of the found bar. This measurement can only be used when you specify Bar as the measurement type. |
The following table includes descriptions of the returned results when you select BC in the UI to enable the return of backward-compatible results.
| Measurement | Definition |
|---|---|
| Number Found | Number of matching features found. |
| Low Level | The level of the signal at the bottom of the edge(s) or bar(s). |
| High Level | The level of the signal at the top of the edge(s) or bar(s). |
| Amplitude | The difference in amplitude between the low level and the high level. |
| Centre | The time of the 50% amplitude level of an edge transition, or the center of a bar (if multiple features found then the average will not apply to and single feature). |
| Rise Time | The time between the 10% and 90% amplitude levels of a rising edge. |
| Fall Time | The time between the 90% and 10% amplitude levels of a falling edge. |
| Width (50% Level) | Width of a single bar or average bar width measured at 50% amplitude. |
Group Delay and Frequency Response (SinX)/X
Pattern(s): (SinX) / X
Definition: This is a measurement of the frequency response (gain) and group delay of a test signal that contains all frequencies in the video bandwidth. All measurements are made relative to a user-specified reference frequency. The positive and negative (SinX) / X pulses may be analysed individually or combined. A high sampling rate and very accurate pulse peak locations are required in order to avoid response anomalies.
| Measurement | Standard | Definition |
|---|---|---|
| Gain | – | Gain, or frequency response, is the gain experienced by the signal at different frequencies relative to a reference low frequency. Results are expressed in dB. |
| Group Delay | – | Group delay represents the delay experienced by the signal at different frequencies relative to a reference low frequency, and will indicate a non-linear phase response. Results are expressed in nanoseconds. |
| Frequency | – | Measurement frequencies defined in the Locations Editor (SinX)/X configuration. |
Horizontal Timing
Pattern(s): Sync and Data Enable
Definition: This is a measurement of the timing of the Sync Pulse and the horizontal blanking and active video intervals. It is assumed that the entire line is made up of the blanking interval followed by the active video interval. Results are given in units of time and sample interval (T).
| Measurement | Definition |
|---|---|
| Sample Interval (T) | Reciprocal of sample frequency. |
| Sync Width | The time between the leading and trailing edges of the horizontal sync pulse. |
| Sync Start | Location of sync start. |
| Sync Start | Location of sync end. |
| Sync H Polarity | Horizontal sync pulse polarity. |
| Sync V Polarity | Vertical sync pulse polarity. |
| Start of Active Video | The time between start of line and start of active video. |
| End of Active Video | The time between start of line and end of active video. |
| Active Line Interval | The time between the first rising edge and last falling edge of active video. |
| Total Line Interval | Total line duration from start of one line to start of next line. |
K Factor
Pattern(s): 2T Pulse and Luminance Bar
Definition: This is a measurement of the amplitude, timing, and distortion of a 2T pulse and luminance bar. The K Factor rating system represents measurements that are weighted according to subjectively determined scales of picture impairment. T refers to the Nyquist interval, which relates to the nominal signal bandwidth. K-Bar is equivalent to the Line Time Distortion measurement. K-50/60Hz is equivalent to the result of the Field Time Distortion measurement divided by two.
| Measurement | Standard | Definition |
|---|---|---|
| Pulse/Bar Ratio | – | The ratio of the peak amplitude of the 2T pulse to the luminance bar amplitude expressed as a percentage of the luminance bar. Pulse amplitude is measured relative to a reference level calculated as the average of the blanking level 1 µs before and after the pulse peak. |
| Pulse/Bar Ratio Error | Rec. 569 §2.5 | The difference between the amplitudes of the pulse and the luminance bar, expressed as a percentage of the luminance bar amplitude |
| K Pulse-Bar | – | A weighted percentage of the difference between the 2T pulse amplitude and the luminance bar amplitude |
| K 2T | Rec. 567 | The greatest weighted amplitude of a positive-going or negative-going echo-term half-wave that is within 1 µs of the 2T pulse leading or trailing edge half-amplitude points |
| Pulse Width (HAD) | – | Also known as Half Amplitude Duration, it is the width of the 2T pulse at its 50% peak level |
Level Meter
Pattern(s): Any Part(s) of Active Line(s)
Definition: This measurement is a level meter single-point or multipoint measurement of the DC level and frequency for the selected components and channels. Measurement modes include Average, Difference, Minimum, or Maximum. You can configure multiple measurements over multiple video lines. Average mode measures the average between the Start and End values on the line. Difference mode requires 2 sets of Operation parameters per measurement result. Minimum mode measures the minimum between the Start and End values on the line. Maximum mode measures the maximum between the Start and End values on the line.
The following table includes descriptions of the UI controls for the level meter.
| Measurement Control | Description |
|---|---|
| Operation | Specifies the measurement type. |
| Operations parameters [Index] | Specifies the number of measurements to configure. You can define the following parameters for each measurement:
|
| Remove | Removes the current indexed measurement in Operations parameters. |
| Empty | Deletes all of the configured measurements in Operations parameters. |
| BC | Enables backward-compatible reporting of measurements. |
| Channel Selection | Specifies which color component channels to include in the measurement. Contains the following options:
|
| Items to report | Specifies which values to report. Contains the following options:
|
| Items to measure | Specifies which values to measure. Contains the following options:
|
The following table includes descriptions of the returned results for the level meter.
| Measurement | Definition |
|---|---|
| Measurement Type | Indicates the type of measurement used, including Average, Difference, Minimum, or Maximum. |
| No of Measurements | Indicates the number of found measurements. A cluster of data appears in the results for each measurement index, x. |
| Color Coding | Indicates the color coding used for the measurements, where 0 indicates YCbCr and 1 indicates RGB. |
| Point x Frame Index | Indicates the frame number of the measurement. |
| Point x Line | Indicates the line of the measurement. |
| Point x Search Start | Indicates the start search index on the video line. |
| Point x Search End | Indicates the end search index on the video line. |
| Point x Color Component Level | Indicates the DC level of the color component at the measurement location. This result repeats three times in each cluster of results, once for each the Y or G, Cb or B, and Cr or R color components, depending on the color coding used. |
| Point x Color Component Frequency | Indicates the frequency of the amplitude tone of the color component found at the measurement location. This result repeats three times in each cluster of results, once for each the Y or G, Cb or B, and Cr or R color components, depending on the color coding used. |
The following table includes descriptions of the returned results when you select BC in the UI to enable the return of backward-compatible results.
| Measurement | Definition |
|---|---|
| Single Point A | Clusters results for a single point marked as A. |
| Color Component Level | Indicates the DC level of the color component. This result repeats three times, once for each Y or G, U/Pb or B, and V/Pr or R, depending on whether YCbCr or RGB color coding is used. |
| Color Component Frequency | Indicates the frequency of the Y or G color component. This result repeats three times, once for each Y or G, U/Pb or B, and V/Pr or R, depending on whether YCbCr or RGB color coding is used. |
| Location or Time | For Average, Maximum, and Minimum measurements, Location indicates the location of the measurement. For Difference measurements, Time indicates the length of time over which the difference measurement is taken. |
Line Frequency
Pattern(s): Sync
Definition: This is a measurement of line period and frequency obtained from the position of consecutive horizontal sync pulses. Field frequency and period (for interlaced signals), or frame frequency and period (for progressive signals) are estimated based on the measured line interval and the number of lines per frame for the selected video standard.
| Measurement | Definition |
|---|---|
| Line Frequency | The reciprocal of the time between the datum point of consecutive horizontal sync pulses |
| Line Frequency Error | The difference between the measured line frequency and the nominal line frequency, expressed as a percentage of the nominal line frequency |
| Line Interval | The time between the datum point of consecutive horizontal sync pulses |
| Field/Frame Frequency | The measured line frequency divided by the number of lines per field (interlaced) or frame (progressive) |
| Field/Frame Interval | The reciprocal of field/frame frequency |
Multiburst (Frequency Response)
Pattern(s): Multiburst
Definition: This is a measurement of the amplitude and frequency of six different frequency bursts in a multiburst signal. It represents the frequency response of the signal.
| Measurement | Definition |
|---|---|
| Reference Amplitude | The amplitude of a low-frequency reference signal on the same line as the multiburst, expressed as raw digital value and in % of full range. |
| Burst Amplitudes | The peak-to-peak amplitude of the largest detected single tone found in the burst signal, expressed in dB and absolute value. |
| Max. Difference | The difference in amplitude between the largest and smallest burst amplitudes. |
| Burst Frequencies | The frequency of the largest detected single tone found in the burst signal. |
Burst frequency depends on the component type and video standard, according to the following table:
| Component | Format | Burst 1 | Burst 2 | Burst 3 | Burst 4 | Burst 5 | Burst 6 |
|---|---|---|---|---|---|---|---|
| R, G, B | 720p, 1080i | 5 | 10 | 15 | 20 | 25 | 30 |
| Y | 720p, 1080i | 5 | 10 | 15 | 20 | 25 | 30 |
| Cb, Cr | 720p, 1080i | 2.5 | 5 | 7.5 | 10 | 12.5 | 15 |
| R, G, B | 480p, 576p | 2 | 4 | 6 | 8 | 10 | 12 |
| Y | 480p, 576p | 2 | 4 | 6 | 8 | 10 | 12 |
| Cb, Cr | 480p, 576p | 1 | 2 | 3 | 4 | 5 | 6 |
Noise Spectrum
Pattern(s): Pedestal or Ramp
Definition: This is a measurement of the RMS level of noise in a quiet signal (ie. no sudden changes in level). Either a Ramp or Pedestal signal may be used. Several filtering options are available to produce the measurement. Measurement is improved by averaging over several lines.
| Measurement | Definition |
|---|---|
| Luminance Noise | The signal-to-noise ratio of a signal with constant pedestal level or slow ramp, expressed in dB relative to the reference of 255 or 235, (for 8 bit) peak-to-peak level. |
| Peak Noise Level | The peak-to-peak noise level of the highest amplitude noise component in the selected band |
| Peak Noise Frequency | The frequency at which the highest amplitude noise component was found |
Non-Linearity
Pattern(s): Staircase or Ramp
Definition: This is a measurement of the non-linearity of amplitude increments in either a staircase or a ramp signal.
| Measurement | Definition |
|---|---|
| Luminance Non-Linearity | The difference between the largest and smallest staircase step amplitudes, expressed as a percentage of the amplitude of the largest step. Non-linearity can be measured using a ramp signal, by measuring the average luminance level at several evenly spaced intervals along the ramp, and calculating the differences between them as pseudo step heights. |
| Step Non-Linearity Errors | The difference between the amplitude of each step and the largest step, expressed as a percentage of the amplitude of the largest step. |
| Largest Step | The step number with the highest step height. |
| Largest Height | Height of the largest step. |
Short Time Distortion
Pattern(s): 1T Luminance Bar
Definition: This is a measurement of the amount of distortion in the rising and falling edges of a luminance bar signal produced by exceeding the nominal bandwidth of the video signal with 1T rise and fall times. T refers to the Nyquist interval, which is equal to the reciprocal of twice the nominal signal bandwidth.
| Measurement | Standard | Definition |
|---|---|---|
| Bar Amplitude | – | The difference in level between the midpoint of the bar and the average of the blanking level measured 1 µs before the bar start location and 1 µs after the bar end location. |
| Bar Width | – | The width of the luminance bar measured between its 50% edge levels. |
| Rise Time | – | The time between the 10% and 90% rising edge levels, where the 0% level is located 1 µs before the 50% level of the leading edge, and the 100% level is measured at the bar center. |
| Rise Preshoot | – | The percentage of rising edge amplitude that undershoots blanking level prior to the start of the rising edge. |
| Rise Overshoot | – | The percentage of rising edge amplitude that overshoots the bar level at the end of the rising edge. |
| Rise Settling Time | – | This is the time from the 50% point of the rising edge until the signal has settled completely within a band centered on the bar center level. The width of the settling band is specified in Advanced Settings (typically 5% of bar center level). |
| Fall Time | – | The time between the 90% and 10% falling edge levels, where the 0% level is located 1 µs before the 50% level of the leading edge, and the 100% level is measured at the bar center. |
| Fall Preshoot | – | The percentage of falling edge amplitude that overshoots the bar level prior to the start of the falling edge. |
| Fall Undershoot | – | The percentage of falling edge amplitude that undershoots blanking level at the end of the falling edge. |
| Fall Settling Time | – | This is the time from the 50% point of the falling edge until the signal has settled completely within a band centered on the post-bar blanking level. The width of the settling band is specified in Advanced Settings (typically 5% of bar center level). |
Sweep (Frequency Response)
Pattern(s): Sweep
Definition: This is a measurement of the amplitude and frequency of a continuous frequency sweep. Measurements are made at a specified number of points between the start and end of the sweep signal. The first amplitude measured at the start of the sweep is used as reference for all other amplitudes, expressed in dB and raw value.
Video Signal Info
Pattern(s): None
Definition: Digital HDMI signals have a wide range of signal characteristics embedded within the signal that you can request to be made available as results for post processing and reporting. These characteristics can be sorted into signal groups whose members share common characteristics. Video Signal Info supports measurement and reporting of one or more signal groups selectable from a list of supported groups. Each report consists of a header describing the report, followed by a report body. The body consists of a number of <parameter name, optional parameter value, optional unit> lines terminated by two blank lines.
Some groups support a low level (byte level) report in addition to the high level report, as selectable by the “High Level Results” selector.
The HDMI standard defines a set of infoframes and packets which provides details about specific parts of the HDMI signal acquired (audio, video, HDMI, vendor information, etc). A separate report is available for a number of these infoframes and packets. Refer to Supported Video Signal Info Reports for a list of supported reports.