Can ColourSpace calibrate displays on a SMPTE ST 2110 network?

Yes. SMPTE ST 2110 replaces SDI cabling with managed IP networks for professional broadcast and post production signals, but the display at the end of the chain is still a display. It is measured, profiled and calibrated in exactly the same way as before.

What changes is how the test patches reach the display, and the metadata that tells the display what kind of signal it is receiving. Both of those need to be right for a calibration to be valid - and both are easy to get wrong in an IP facility, as signals often pass through gateways and processing nodes that can silently alter them.

IP changes the cabling, not the colour science.

This page covers a vendor-neutral way to calibrate ST 2110 displays with ColourSpace today, the checks needed to make sure the IP path is not altering the patches, and a reference table showing how ST 2110 signals colour information compared to SDI and HDMI.

How do you send ColourSpace test patches over ST 2110?

The simplest approach uses equipment most facilities already have: an SDI test pattern generator (TPG) supported by ColourSpace, feeding an SDI to ST 2110 gateway. No ST 2110 capability is needed in ColourSpace or the TPG itself - the gateway handles the IP side.

The signal path

  1. ColourSpace controls the TPG and the probe exactly as it would on any other system.
  2. SDI TPG outputs the calibration patches over SDI, in the format the display will be used with.
  3. SDI to ST 2110 gateway converts the SDI signal to an ST 2110-20 stream, locked to the facility's PTP timing (SMPTE ST 2059-2).
  4. The ST 2110 network routes the stream to the display, usually under control of the facility's broadcast controller (NMOS IS-04/IS-05 or a vendor control system).
  5. The display receives the stream on a native ST 2110 input, or via an ST 2110 to SDI gateway in front of an SDI display.
  6. The probe measures the display and connects back to ColourSpace as normal. Where the display supports it, LUT upload and display control also work as normal over the network.

Practical points

  • Calibrate through the input that will be used. Many professional monitors store calibration per input or per signal mode, so a calibration made via a local SDI input may not apply to the IP input. Either calibrate through the ST 2110 path, or verify the result through it.
  • Allow for path latency. Gateways, frame synchronisers and the network all add delay. Static calibration patches are unaffected by an occasional dropped or repeated frame, but each new patch must have fully reached the display before it is measured - increase the patch delay in ColourSpace if readings appear to lag behind patch changes.
  • Use the operational format. Set the TPG to the resolution, frame rate, sampling, bit depth and HDR/SDR mode the display will actually be used with, so the gateway and display are exercised in the same configuration they run in day to day.

What should be checked in an SDI to ST 2110 gateway before calibrating?

A gateway that alters the signal will produce a calibration that is accurate for the wrong input values. These are the points to verify before trusting any measurements made through an IP path.

1. Signal range

Range errors are the most common problem. ST 2110 signals range with the RANGE parameter - NARROW (the default if it is absent), FULLPROTECT or FULL - while SDI generally does not signal range at all, relying on convention and manual settings. Check that the gateway passes code values straight through, without rescaling between narrow and full range, and that the RANGE value it declares matches what the TPG is actually sending. Patches at and beyond the nominal black and white levels (for example 10-bit code values 64 and 940, plus values below and above them) will quickly show any clipping or rescaling.

2. Colorimetry and transfer signalling

The display uses the stream's signalling to select its mode, so incorrect metadata can put a correctly calibrated display into the wrong mode. Check that the gateway translates the SDI payload ID (SMPTE ST 352) colorimetry and transfer characteristic into the correct ST 2110 colorimetry and TCS values. Some gateways ignore the incoming payload ID and declare fixed values (often BT709 and SDR) unless set manually. Most gateways show the stream's SDP in their web interface, or it can be viewed in the facility's NMOS controller.

3. Sampling and bit depth

Check whether the gateway preserves the incoming sampling (RGB 4:4:4 or YCbCr 4:2:2) and bit depth, or converts them. Conversions add matrix rounding and chroma filtering, both of which change patch values - especially on small or saturated patches. Using full field or large window patches reduces the effect of chroma filtering, but avoiding the conversion is better.

4. No processing in the path

Many gateways include processing features - colour correction, legalisers or clippers, HDR/SDR conversion, scaling and sharpening. All of these must be bypassed for calibration, both in the sending gateway and in any processing node or receiving gateway the stream passes through.

5. Uncompressed video only

The calibration path should use uncompressed ST 2110-20. See below for why JPEG XS (ST 2110-22) should be avoided.

A simple path test

If the display also has a direct SDI input that shares the same calibration, measure the same patch set both directly over SDI and through the IP path, and compare the results in ColourSpace. Any difference beyond normal probe repeatability points to the IP path altering the signal, and should be resolved before calibrating.

How does SMPTE ST 2110 signal colour space, transfer function and range?

In ST 2110, a stream is described by its SDP (Session Description Protocol) file, which carries the parameters a receiver needs to interpret the video. These parameters do the same job as the payload ID on SDI, and the InfoFrames on HDMI. The table below lists the equivalent signalling across all three.

Colour signalling equivalents: SDI, SMPTE ST 2110-20 and HDMI
Property SDI (SMPTE ST 352 payload ID) ST 2110-20 (SDP parameter and values) HDMI (InfoFrames)
Colour space / primaries Colorimetry field (for example Rec.709 or Rec.2020) colorimetry= BT601, BT709, BT2020, BT2100, ST2065-1, ST2065-3, XYZ, UNSPECIFIED AVI InfoFrame colorimetry / extended colorimetry
Transfer function Transfer characteristic field (SDR-TV, HLG, PQ) TCS= SDR (default), HLG, PQ, LINEAR, BT2100LINPQ, BT2100LINHLG, ST2065-1, ST428-1, DENSITY, UNSPECIFIED Dynamic Range and Mastering InfoFrame EOTF
Signal range Not generally signalled - narrow (legal) range by convention, set manually otherwise RANGE= NARROW (default), FULLPROTECT, FULL AVI InfoFrame quantisation range
Sampling Sampling structure field sampling= for example RGB, YCbCr-4:4:4, YCbCr-4:2:2, YCbCr-4:2:0, ICtCp-4:2:2 AVI InfoFrame colour format
Bit depth Bit depth field depth= 8, 10, 12, 16, 16f (16-bit float) Deep colour signalling

Common combinations

Typical ST 2110-20 parameter combinations
Signal colorimetry TCS
SDR HD (Rec.709) BT709 SDR
Wide gamut SDR (Rec.2020) BT2020 SDR
HLG HDR BT2100 HLG
PQ HDR BT2100 PQ

As an example, the format line of an SDP file for a 1080p50, 10-bit, YCbCr 4:2:2, HLG stream looks like this:

a=fmtp:96 sampling=YCbCr-4:2:2; width=1920; height=1080; exactframerate=50; depth=10; TCS=HLG; colorimetry=BT2100; RANGE=NARROW; PM=2110GPM; SSN=ST2110-20:2017; TP=2110TPN

Note that ST 2110-20 can carry RGB 4:4:4 at 10, 12 or 16 bits, avoiding the chroma subsampling common in SDI chains. Where both the gateway and display support it, an RGB 4:4:4 path is the cleanest option for calibration.

Can JPEG XS (ST 2110-22) be used for display calibration?

It should be avoided. ST 2110-22 carries compressed video, most commonly JPEG XS, to reduce network bandwidth. JPEG XS is designed to be visually lossless, not mathematically lossless, so the code values that reach the display are not guaranteed to be the values ColourSpace sent. Any difference becomes an error built into the calibration.

Calibration and verification should always use uncompressed ST 2110-20. If a display is normally fed with JPEG XS, calibrate it with an uncompressed stream - the calibration describes the display, not the compression.

Calibrating an ST 2110 facility?

If you are planning display calibration for an ST 2110 facility, OB truck or IP-based post production environment, contact Light Illusion to discuss your setup. For general information on ColourSpace, see the ColourSpace page, and for background on HDR signals see What is HDR?