TEKTRONIX 4K/UHD Monitoring and Measurement Guidelines

External reference calibration (optional):

If higher accuracy is required, a black field or three-level reference signal can be connected to the "External Reference" port of the instrument to compare the timing of Link A with the reference signal and further calibrate the link delay.

Question 2: What is the role of VPID (Video Payload Identifier) in 4K/UHD systems? How to verify the correctness of VPID through Tek 8000 series devices, and what are the common errors?

Answer: VPID is based on the SMPTE ST 352 standard and stored in the SDI auxiliary data area. Its core function is to enable devices to quickly recognize video formats (resolution, number of links, sampling rate, color gamut, etc.), avoiding manual configuration errors. It is a "format passport" compatible with multiple 4K/UHD devices.

1、 Steps to verify VPID for Tek 8000 series:

Quick verification of video sessions:

Open the "Video Session" display (Page 1) and view the "352M Payload" field (i.e. UDW1-4 bytes of VPID) for each link:

The four links must meet the following requirements: UDW1-3 (format information) is completely consistent (such as 89h CAh 00h), UDW4 (link number) is 01h → 41h → 81h → C1h according to A → D;

ANC Data Inspector deep validation:

Go to "ANC Data Inspector", filter for "DID/SDID=41/01" (VPID identification), and view:

Checksum (Exp/ACT Chksum): must be consistent, otherwise VPID data will be damaged;

Location information: Normal VPID is located at "Field1/Line9", abnormal location may cause the device to not recognize it;

Datalist locates sample level information:

Based on the "Line" and "Sample" displayed by the ANC Inspector, locate the VPID packet in the "Datalist" and confirm that UDW1-4 bytes have no bit errors (such as stuck bits).

2、 Common VPID errors and reasons:

Link number error: UDW4 is not in the order of A → D (01h/41h/81h/C1h), such as Link B/C exchange, resulting in device splicing image misalignment;

VPID duplication/missing: If there are multiple VPIDs on the same link or if a link does not have a VPID, the device cannot determine the format, resulting in an "unknown format" error message;

Checksum mismatch: Data is damaged during signal transmission, and cable shielding needs to be checked or intermediate equipment (such as SDI distributor) needs to be replaced.

Question 3: How to choose between BT.709 and BT.2020 color gamut in K/UHD content creation? How to verify the correctness of color gamut settings through testing signals with Tek 8000 series devices?

Answer: Color gamut selection needs to be combined with content usage and display device capabilities, and verification relies on standard test signals and professional monitoring tools, as follows:

1、 Color gamut selection principle:

Choose the scene for BT.709:

The content needs to be compatible with traditional HD devices (such as old TVs and HD players);

The production environment does not have BT.2020 display devices (such as the monitor only supporting BT.709) to avoid color deviation in the later stage;

Choose the scene for BT.2020:

4K HDR content (such as movies and high-end TV programs) needs to utilize a wide color gamut to enhance color richness;

The target display device supports BT.2020 (such as 4K HDR TV, professional cinema projection).

2、 Color gamut correctness verification steps (using Tek 8000 series):

Prepare test signal:

Generate a "100% split color bar signal" (left half BT.709, right half BT.2020), ensuring that the signal contains RGB three channel full range levels (0% -100%);

Switching instrument color gamut settings:

Go to "CONFIG MENU>Colorimetry", select "BT.709" and "BT.2020" respectively, and observe the RGB waveform display:

Correct setting: The RGB level of the corresponding half is stable at 0% (0mV) and 100% (700mV) without fluctuations;

Error setting: The RGB level of non corresponding half deviates by 0%/100% (for example, under BT.709 setting, the green level of BT.2020 half is only 80%);

Comparison brightness and color difference formula:

Go to "MEAS>Amplitude>Y" and measure the brightness value:

BT.709：Y=0.2126R'+0.7152G'+0.0722B'， The Y value of the white color bar is approximately 700mV;

BT.2020：Y=0.2627R'+0.6780G'+0.0593B'， The Y value of the white color bar is approximately 680mV;

If the values match, the color gamut setting is correct, and if the deviation exceeds 5%, it needs to be readjusted.