HDR Calibration

The calibration of HDR, specifically HDR TVs, is presently what is known as a Crap Shoot... For the real videophile there is presently no truly accurate way to calibrate HDR TVs, although Light Illusion is working with various manufacturers to change this situation.

Most professional HDR grading displays can be accurately calibrated, as they have internal 3D LUT calibration, and are integrated with ColourSpace

HDR

HDR has had something of a difficult birth, with different display manufacturers effectively defining their own HDR, specifications, based loosely around a set of common specifications.

Having said that, there is nothing to stop a standard gamut display (Rec709), with standard HD or even SD resolution, working with HDR dynamic range for example. A number of professional HDR grading displays are actually HD resolution, not UHD (4K).

The HDR standards, such as they exist, are aimed more at consumer viewing, including BluRay players, as well as HDR TVs.

For the sake of simplicity within this guide, we will assume that HDR TVs means UHD 4K resolution, ST2084 (PQ) HDR EOTF, and Rec2020 colour gamut, using HDR10, HDR10+, & Dolby Vision, as well as HLG.

HDR Grading Displays

The calibration of grading displays is, in the main part, very simple with ColourSpace, with little difference from SDR calibration. Many HDR grading displays, from manufacturers such as FSI, Canon, ASUS, Eizo, Konvision, Kroma, etc., are fully integrated with ColourSpace, and use 3D LUT calibration for HDR exactly as for SDR.

HDR calibration for professional grading displays is explained in more detail at the end of this page.

HDR TVs

User calibration of home HDR TVs is actually something of an oxymoron...

For a number of reasons, there is presently no viable way to directly, and accurately, calibrate HDR on HDR TVs.

For most videophiles, home cinema calibration means taking control of all aspects of the display's image path, enabling precise control to be attained over all the display's colourimetry. Often, this means using 3D LUT based calibration, as this is the pinnacle of all calibration techniques.

With SDR TVs, external LUT boxes, such as the Lumagen Radiance, as well as the software based madVR playback system, can be used to very accurately calibrate connected displays, using ColourSpace to generate the 3D calibration LUT.

Direct internal 3D LUT based calibration of home TVs is a limited option as few TV manufacturers offer in-built 3D LUT capability... This lack of in-built 3D LUT capability also extends to new HDR TVs, as not one has in-built 3D LUT capability for HDR use.

The issue with HDR TVs is there are few viable ways to calibrate them with 3D LUTs, as even though LUT boxes, such as the Lumagen Radiance Pro and MadVR/Envy, can work with HDR images, most HDR TVs have their factory EOTF presets fixed, and cannot have them disabled, while still maintaining HDR compatibility. This makes secondary, external LUT Box calibration impossible.

Consequently, HDR TV calibration is, in the main, nothing more than limited manual adjustments.

Light Illusion Manufacturing Partners

Light Illusion is working on HDR TV calibration with various TV manufacturers and hardware manufacturers, and we hope to have better calibration approaches for home TVs in the near future, including 3D LUT based HDR calibration.

The first home TV manufacturer to offer accurate HDR TV calibration in partnership with Light Illusion will be announced soon!

COMPLAIN TO YOUR HDR TV SET MANUFACTURER AND DEMAND THEY ADDRESS THESE ISSUES!

A very unique capability of ColourSpace HDR calibration is the ability to perform Increased Resolution PQ LUT calibration.

Light Illusion will be delighted to assist any TV manufacturers that wish to address correct HDR calibration.

HDR TV Calibration

For home HDR TVs, the lack of viable 3D LUT calibration capability leaves us with Manual Calibration...

The problem with manual display calibration is that few displays (including traditional SDR Rec709 displays) are designed to calibrate accurately through the use of the display's available manual controls - including the guesswork based AutoCal some calibration systems promote. This can be due to poor internal image processing electronics, with poor colour decoupling (RGB cross-colour contamination) for example, which causes the controls to not work as expected, or due to simple poor implementation of the display's CMS (Colour Management System).

This is why true videophiles use 3D LUT boxes for SDR Rec709 display calibration accuracy, as this negates all the display's internal design issues, and produced the best possible final calibration.

And HDR TVs are no exception. They suffer the same issues and limitations with respect to accurate manual calibration.

So, as there are no viable ways to calibrate home HDR TVs via 3D LUTs, we are limited by the level of accuracy in-built into the display by the manufacturer. But, what exactly does this mean for HDR HDR TV calibration?
(As mentioned above, the issue is that at the present time there are no home HDR TVs with 3D LUT calibration capabilities, and most do not allow for their in-built EOTF to be disabled, making external 3D LUT Box calibration unusable...)

With SDR TVs, calibration is based on matching the TV as closely as possible to a given standard, such as Rec709 with a power law EOTF (we do not recommend the use of BT1886). With HDR TVs there is a further issue as the target colour space is Rec2020, which no TV can attain. This means the TV cannot be calibrated directly to the standard, as only a small part of the Rec2020 gamut will be covered by the display. Additionally, the ST2084 HDR EOTF is not relative, as it is a nits based absolute standard, based on a 10000 nit maximum luminance standard. This means different displays with different peak luminance levels will use a different portion of the full ST2084 EOTF, with different Tone Mapping roll-off.

The result is this is less about calibration standards, and more about the process the display manufacturer enables any user to adopt for manual calibration. There is really no calibration being performed, as the process used just verifies display setting, such as maximum luminance, black/white points of the display, the grey scale, and peak RGB gamut values, and then hopes the display's own processing will correctly place the volumetric colours where they should be within the target colour space.

Unfortunately, this is the basic reality of HDR TV calibration.

HDR10, Dolby Vision, and HLG

At the moment there are three competing HDR standards - HDR10 (and HDR10+), Dolby Vision, and HLG (Hybrid Log-Gamma).

Dolby Vision is a proprietary format, and requires all elements in the image chain to be Dolby licensed, providing a relative guarantee of final image display.

HRD10 and HDR10+ are open standards, so lack the adherence to fixed standards for image playback, with each display manufacturer defining their own internal HDR processing.

Note: the underlying calibration of HDR10, HDR10+, and Dolby Vision is identical, as all use the same target colour space PQ EOTF and Rec2020 Gamut - the same calibration should work for all standards.

HLG is simpler to calibrate as it is a Relative standard, and uses a similar approach to SDR calibration, including the ability to easily use external LUT boxes for 3D based calibration.

PQ Based HDR Manual Calibration with ColourSpace

Understanding the above, the first stage for any HDR calibration is about profiling the display to assess its present level of accuracy, and involves using a patch generator connected to the ColourSpace laptop to inject the correct metadata into the signal chain, which triggers the display's HDR capabilities. Without the correct metadata in the HDMI signal path most home HDR TVs will default to SDR operation, so will not profile as expected for HDR.

If the TV/display can be manually switched into HDR mode there is no need for a special HDR signal generator - any patch generator will work as required.

Ideal pattern generators for this include the Murideo SIX-G & SEVEN-G, and Radiance Pro LUT Boxes, and the very cheap Raspberry Pi based PGenerator, as they will all act as patch generators, and insert the required HDR metadata into the signal path.

An alternative to an actual patch generator is to use a HDfury box to inject the required metadata into the HDMI signal path.

HDfury

An alternative HDR metadata insertion is the HDfury box, which can be used within the HDMI signal path from the ColourSpace laptop to the HDR TV, injecting the required metadata into the signal path.

Using a HDfury box can make use of the in-built ColourSpace TPG for direct display profiling, using the HDfury's own control program to pre-set the required HDR metadata settings.

With this configuration any HDR display can be profiled with ColourSpace.

HDR Metadata

Using the HDFury GUI add the required custom HDR Metadata.
(Always tick the REC.2020 flag)

Custom Metadata (P3 Primaries, 0.005 Black / 1000 nits Peak / 1000 MaxCLL / 400 MaxFALL): 87:01:1a:74:02:00:c2:33:c4:86:4c:1d:b8:0b:d0:84:80 :3e:13:3d:42:40:e8:03:32:00:e8:03:90:01
Custom Metadata (P3 Primaries, 0.005 Black / 4000 nits Peak / 1000 MaxCLL / 400 MaxFALL): 87:01:1a:b0:02:00:c2:33:c4:86:4c:1d:b8:0b:d0:84:80 :3e:13:3d:42:40:a0:0f:32:00:e8:03:90:01

And set the required custom AVI InfoFrame.
For PC/Laptop with HDMI 1.x and PGenerator, set output RGB-Data and patch scale 16-235 while for AccuPel and DVDO AVLab set RGB-Video output with no patch scale.

82:02:0D:AE:00:E8:64:10:00:00:00 for 1080p60 RGB
82:02:0D:AE:00:E8:64:20:00:00:00 for 1080p24 RGB

For DVDO AVLab, as an additional option RGB-Video 2160p24 8-bit output can be used

82:02:0D:AE:00:E8:64:5D:00:00:00 for 2160p24 RGB

For PC/laptop with HDMI 2.0 output, RGB-Data and patch scale 16-235 can be used

82:02:0D:AE:00:E8:64:51:00:00:00 for 2160p60 RGB

With the Murideo SIX-G & SEVEN-G, PGenerator, and Radiance Pro or HDFury correctly configured for HDR metadata, and connected both to the ColourSpace laptop and the HDR display to be profiled, put up a small size (approx. 10% by area) patch window.

Record the 100% peak white value. This peak white value needs to be used to generate and save a new ST2084_Rec2020 colour space for the specific HDR display being calibrated, using this maximum peak luminance value as the clip point for the display. Name the new colour space something you will easily remember.
Note: If the white point of the display is not accurate to D65, a lower Nits value should be used as calibration will force the peak value lower.

The saved colour space can then be used as the target colour space for the standard manual calibration approach for the given display for grey scale, and EOTF, as much as the display allows for.

Note: For Dolby Vision 2.0 Calibration the new ST2084 colour space is not used, as the manual grey scale calibration is aimed at the display's default 2.2 EOTF. See below.

After manual calibration has been performed, the new ST2084 colour space can be used to verify the calibration using Display Profiling as normal.

Example PQ Based HDR Calibration

The following shows a couple of examples of the extremely limited HDR calibration offered by TV manufacturers for HDR TVs.

LG TV HDR Setup

LG's documentation for UHD Alliance Greyscale Tracking is a very good example of HDR TV calibration limitations.

The guide has no colour calibration component at all - it is just setting the greyscale (as the document title states), and setting the white point to D65.

The TV makes the assumption that all UHD material is graded to P3 primaries (which is presently true, although there is no guarantee to that fact, and in reality is an incorrect step, as all UHD consumer sources have the material mapped into Rec2020 gamut as the delivery container!), and then assumes that the internal colour management of the TV is good enough to correctly map all volumetric colour space accurately.

And as all Home Cinema enthusiasts know, no TV manufacturers ever gets that right with SDR TVs. So why should HDR be any different?

Dolby Vision Golden Reference

Another example of the limited HDR calibration offered by TV manufacturers can be seen here with the original Dolby Vision Calibration Guide for Vizio displays.

The guide describes nothing more than a setup of the display through greyscale measurements, and a validation that the display's peak colour values matched against the Golden Reference file for the Vizio display.

The Golden Reference file simply contains the expected maximum primary and secondary colour gamut plots, and the 'calibration' process is simply to match the displays (if possible) to these targets, and then assumes that the internal colour management of the TV is good enough to correctly map all volumetric colour space accurately.

Note: The use of Golden Reference files has since been abandoned, with the introduction of Dolby Vision Calibration 2.0. However the reason for the abandonment is a very good example of the issues facing manual HDR calibration, The unit-to-unit variation of TVs of the same exact model from the same manufacturer vary too much for a single golden reference to be a valid target across the board.

Dolby Vision Calibration 2.0

Dolby Vision Calibration 2.0 is a better approach, as it disables the display's PQ EOTF, but maintains the display in peak luma mode.

The display can then be manually calibrated as normal for grey scale, targeting the screen's default 2.2 gamma curve, and measurements made for the peak RGBW primaries.

The peak RGBW values are then saved to a Dolby Vision reference file, and uploaded into the TV via USB. The internal Dolby Vision processing with the display then maps the display's HDR capabilities to the target PQ EOTF and Rec2020 colour space.

While still somewhat short of true 3D LUT based calibration, this can be viable manual approach to HDR calibration.

However, there is a real issue with final calibration accuracy when attempting to profile a display with a 2.2 EOTF (especially with HDR peak brightness levels), when targeting a PQ EOTF. The excessive curvature of the PQ EOTF vs. a 2.2 power law EOTF means most calibration will become inaccurate, and introduce banding and artefacts into the image, especially in the shadows.

Because of this, Light Illusion has introduced a unique Limit Range approach to HDR calibration, as defined within the Advanced Operation page of the website within the PQ (ST2084) based HDR section, and which has already been adopted by professional display manufacturers, including FSI.
This new, and accurate, approach to HDR calibration could easily be adopted by HDR TV manufacturers.

Note: the underlying calibration of HDR10, HDR10+, and Dolby Vision is identical, as all use the same target colour space PQ EOTF and Rec2020 Gamut - the same calibration should work for all standards.

PQ Based HDR 3D LUT Calibration with ColourSpace

With professional display no metadata is needed to put the display into HDR mode, meaning direct profiling can be used, either via a patch generator, or via direct HDMI output from the ColourSpace laptop, following the standard ColourSpace 3D LUT approach to Display Calibration.

This is explained in some detail within the Advanced Operation page of the website, within the PQ (ST2084) based HDR section.

HLG Manual & 3D LUT Calibration with ColourSpace

Calibration of HDR displays to the HLG standard is a far simpler process, as the approach is basically identical to standard SDR calibration, with no metadata requirement, and as it is a relative standard, rather than PQ's absolute standard, it effectively self-scales to any display's peak luminance capabilities.

As with PQ based HDR, a new user defined colour space must be generated to match the peak luma of the display being calibrated, using the System Gamma option as well as setting the desired Surround Luminance value.

With the new user colour space defined, 3D LUT based calibration can be performed as usual, with the new colour space as the calibration target.