How to use the LG 2019 PQ Curve Upload Template for DeviceControl Interface with LG 2019 OLED TV's.
LG 2019 OLED TV's feature a Dynamic Tone Mapping algorithm (Picture -> Picture Mode - Setting -> Expert Controls).
When Dynamic Tone Mapping is enabled 'On', the HDR10 tone-mapping curve will be dynamically generated after analysis of signal peak and histogram information on a frame by frame basis.
When Dynamic Tone Mapping is disabled 'Off', the LG TV will use the default 'factory' HDR10 tone curve parameters (Peak Luminance, 3x Tone Curve Metadata Point and 3x Roll-Off Point) and will determinate the PQ Luminance of content based to the HDR10 compliant stream static metadata info (SMPTE ST.2086, MaxFALL and MaxCLL) as follows:
Use ST.2086 Mastering Metadata -> Mastering Display Color Volume -> 'Maximum Display Luminance' value.
If 'MaxCLL' (Content Metadata -> Maximum Content Light Level) is present and lower than the 'Maximum Display Luminance' value, it will use MaxCLL value.
If ST.2086 Maximum Display Luminance and MaxCLL are both signaled as zero (as defined for un-available), it assumes and use 4000 nits values as 'Maximum Display Luminance'.
LG 2019 OLED TV's PQ Curve Upload Template is providing a GUI (Graphical User Interface) to configure and upload these 7 tone-mapping engine calculation parameters data values to the TV, to match the actual measured (calibrated) peak luminance of your display; for the tone-mapping calculations to be more accurate and also to adjust the roll-off point for 3 different user-specified mastering display peak values (Maximum Display Luminance of HDR10 ST.2086 static metadata) of your HDR10 content.
That template can be used from any LG 2019 OLED TV user, even if his display has been calibrated or not. It doesn't matter what calibration software will be used to calibrate the LG 2019 OLED TV in HDR10 mode.
When the user has calibrated the display using HDR10 patterns, it will be required to set his measured 100% White calibrated peak output 'nits' to the 'Peak Luminance' parameter value.
For users without any calibration instrument/software who want only to test different tone-mapping parameters, then the default '700' nits value to the 'Peak Luminance' parameter should be used.
For users with calibrated displays from professional calibrators, its not recommended to change any value unless they can get the info from their professional calibrator of what value for Peak Luminance parameter its been uploaded after calibration, as there no way to see what value the professional calibrator has entered internally to the LG 2019 OLED TV.
As a tip, the panel Peak Luminance number in nits can be found to the professional calibrator post-verification grayscale report. This is a detail the user has to discuss with the professional calibrator first, before adjusting the Peak Luminance parameter. When the user will know the Peak Luminance parameter value, then any custom adjustment upload of other parameters it will not alter/undo the current calibration, it will only change the tone-mapping behavior.
The Peak Luminance parameter is the most important setting for the proper tone-mapping engine calculations.
HDR10 Tone Mapping default 'factory' parameters values
Metadata Point 1:
Roll-Off Point 1:
Metadata Point 2:
Roll-Off Point 2:
Metadata Point 3:
Roll-Off Point 3:
Use these values above if you want to restore the 'factory' default tone-mapping parameter values.
Explanation of HDR10 tone mapping engine parameters
Used to set the target output luminance range for tone-mapping engine calculations. Measure your calibrated peak white using a 100% White pattern (940 digital level) with 10% window size (L32 loading) pattern with black background. The 'nits' number of that peak white measurement it will be the 'Peak Luminance' value of that panel.
To verify how the roll-off point value affects the PQ curve tracking, you have to generate HDR10 patterns with the same 'Maximum Display Luminance' value as the Metadata Point number (1,2 or 3) value you want to test.
'Maximum Display Luminance' is the peak luminance of the mastering monitor used for color grading of each HDR10 title. Currently, industry is using 1000/1100/4000 or 10000 nits capable post-production monitors. The 'Maximum Display Luminance' info is part of each movie HDR10 Metadata InfoFrame.
Tone Curve Metadata Point (3x):
Used to define which content metadata peak luminance 'Maximum Display Luminance' value you are defining the tone curve for.
You have the option to define the TV tone-mapping engine behavior (based to the entered roll-off point setting) for 3 different 'Maximum Display Luminance' (peak luminance of the mastering monitor used for color grading) scenarios.
For example, if you set to 'Tone Curve Metadata Point 1' the '1000' nits value, when you will playback a movie with HDR10 Metadata of 1000 nits @ 'Maximum Display Luminance', the TV will adjust the tone-mapping based to the entered 'Roll-Off Point 1' value for that content.
As there available 3x Tone Curve Metadata Point selections, it's up to the user preference which 3 different values he will pre-define.
To provide more help to the user's decision for these 3 'Tone Curve Metadata Point' values, from a very large list I personally keep with HDR10 metadata of many titles, below you will find a summary of current 'Maximum Display Luminance' values HDR10 titles are using:
Roll-Off Point (3x):
Used to set the point at which the tone curve deviates from PQ, expressed as a percentage of the Peak Luminance value.
With the 3 Metadata and Roll-Off Points, it is possible to accurately define tone curves for content with 3 specified metadata points; as example, for 1000/4000/10000 nits peak content.
Content with metadata peak luminance 'Maximum Display Luminance' value different or between these points. it will result in a tone curve that is interpolated between the three defined values.
If a PQ-EOTF 'Hard Clip' is desired regardless of content metadata the TV will receive, for content creation purposes, or to use the display as a PQ-EOTF reference, this can be easily achieved by setting all three Roll-Off Parameters to 100%.
It will be interesting about which will be the calibration results if the user will calibrate with PQ curve parameters applied to provide a 'Hard Clip' and then after the calibration to restore them back to normal values.
Using that 'Hard Clip' method, you can calibrate using the normal TV RGB Balance controls but without any PQ curve tone-mapping active.
If content metadata signals a peak luminance lower than the 'Peak Luminance' Tone Curve Parameter, a Peak Hard Clip tone curve will be used, tracking PQ up to the Peak Luminance Tone Curve Parameter and clipping content at higher luminance.
When you are calibrating HDR10 using the available to normal TV menu RGB balance controls (without bypassing the HDR10 Tone-Mapping processing math's), all these available RGB Balance controls adjustments are taking place in Gamma space. If the panel peak luminance is higher or lower that the assumed peak luminance of the HDR processing math’s, you may find yourself pushing the grayscale adjustments in odd directions to compensate, resulting in the potential for banding.
Banding also called as false contouring or posterization, refers to unrealistic solid strips of color in areas that should display a smooth transition.
How HDR10 PQ-Curve Tone Mapping works?
An HDR image is encoded using a perceptual quantizer opto-electrical transfer function (hereinafter, PQ-OETF) defined by the society of motion picture and television engineers (SMPTE) ST.2084 and has a high dynamic range of 0 to 10000 nits.
LG 2019 OLED TV will need to perform an image processing procedure using a perceptual quantizer electro-optical transfer function (PQ-EOTF) defined in SMPTE ST.2084, in order to display an HDR image.
When the peak luminance output capability of the LG 2019 OLED TV is not matching the luminance level performance of the mastering monitor used for content mastering, then some tone-mapping processing have to be applied.
Tone-Mapping procedure remaps luminance from the source values to the lower values the display can reproduce.
The LG 2019 OLED TV Tone-Mapping image processing module utilize 2 mapping functions.
When the content will have 'Mastering Display Color Volume -> Maximum Display Luminance' value equal or lower from PQ Curve Tone-Mapping 'Peak Luminance' parameter or when the MaxCLL number is lower from content 'Mastering Display Color Volume -> Maximum Display Luminance' value, then the calibrated TV will track accurately the PQ-EOTF up to 'Peak Luminance' value and it will hard-clip above of that value. In that case the TV's Tone-Mapping image processor will use only the first tone-mapping function and it will bypass the second tone-mapping function (roll-off).
When the content will have 'Mastering Display Color Volume -> Maximum Display Luminance' value higher from PQ Curve Tone-Mapping 'Peak Luminance' parameter, then the image processor will see if the Metadata point 1, 2 or 3 has the exact same value as the content 'Mastering Display Color Volume -> Maximum Display Luminance'. If there present such entry, then the second mapping function will be enabled, using the entered percentage value of the 'Roll-Off Point' value for the roll-off calculation, based to the 'Peak Luminance' entered value.
In that case, the TV's Tone-Mapping image processor will use the first tone-mapping function to track accurately the PQ-EOTF up to the entered percentage value of 'Roll-Off Point' (knee point), based to the 'Peak Luminance' value and it will deviate from PQ-EOTF by using a smooth Roll-Off curve until the 'Peak Luminance' value.
The Roll-Off works as a form of compression, so when the content was been mastered for 4000 or 10000 nits, the compression will be even higher.
You can see to the picture below how Tone-Mapping works; with detailed explanation; when you have an LG 2019 OLED TV panel with 820 nits calibrated peak output, using the default Metadata Point & Roll-Off Point parameter values:
When you have upload to all 'Roll-Off Point' parameters 100% values, then the tone mapping processor will track accurately the PQ-EOTF up to 820 nits and it will 'hard clip' the content above to the entered 'Peak Luminance' parameter value (820-10000 nit code values).
Tone Map 1:
When you have a panel with calibrated peak output of 820 nits as entered to the 'Peak Luminance' value parameter, and have configured the Metadata Point 1: 1000 nits / Roll-Off Point: 70%, when the 'Mastering Display Color Volume -> Maximum Display Luminance' value of the content will have 1000 nits, initially the tone-mapping processor with remap the content dynamic range 0-1000 nits to match the panel dynamic range 0-820 nits and then perform a hard clip of 1000-10000 nit code values of the content.
The first tone-mapping function will track accurately the PQ-EOTF up to 70% of the Peak Luminance until 574 nits (820 nits peak * 0.7 roll-off = 574 nits) and the second tone-mapping function will tone map the code values of 574-1000 nits using a smooth rollover curve to match the panel 574-820 nits range.
Tone Map 2:
When you have a panel with calibrated peak output of 820 nits as entered to the 'Peak Luminance' value parameter, and have configured the Metadata Point 2: 4000 nits / Roll-Off Point: 60%, when the 'Mastering Display Color Volume -> Maximum Display Luminance' value of the content will have 4000 nits, initially the tone-mapping processor with remap the content dynamic range 0-4000 nits to match the panel dynamic range 0-820 nits and then perform a hard clip of 4000-10000 nit code values of the content.
The first tone-mapping function will track accurately the PQ-EOTF up to 60% of the Peak Luminance until 492 nits (820 nits peak * 0.6 roll-off = 492 nits) and the second tone-mapping function will tone map the code values of 492-4000 nits using a smooth rollover curve to match the panel 492-820 nits range.
Tone Map 3:
When you have a panel with calibrated peak output of 820 nits as entered to the 'Peak Luminance' value parameter, and have configured the Metadata Point 3: 10000 nits / Roll-Off Point: 50%, when the 'Mastering Display Color Volume -> Maximum Display Luminance' value of the content will have 10000 nits, initially the tone-mapping processor with remap the content dynamic range 0-10000 nits to match the panel dynamic range 0-820 nits.
The first tone-mapping function will track accurately the PQ-EOTF up to 50% of the Peak Luminance until 410 nits (820 nits peak * 0.5 roll-off = 410 nits) and the second tone-mapping function will tone map the code values of 410-10000 nits using a smooth rollover curve to match the panel 410-820 nits range.
Ideally, for the most accurate calibration and for keeping as high as possible the artistic intent of the content, it will be to disable any tone-mapping, so to let the display follow the PQ-EOTF up to the maximum nits the panel can output. This can be performed by uploading to all 'Roll-Off Point' parameters to 100% values. Doing this, the panel will track as best as possible the PQ-EOTF and it will 'hard clip' the content above to the entered 'Peak Luminance' parameter value.
Below there is a summary of the available post-production monitors for color grading of HDR content in the market; including some prototype models also:
The black level luminance level has been estimated based to the manufacturers published contrast ratio specifications.
Reference monitors used for content color grading are calibrated to follow as best as possible the PQ-EOTF up to the nits they are capable to output and they will 'hard-clip' the nits can't able to reach, without any kind of not tone-mapping applied. The same it's happening with gamut calibration also, there not any gamut mapping applied.
Its recommended the post-production monitors to be calibrated and masters using P3 colorspace with D65 white point, rather than using REC.2020, since P3 is typically the largest realizable and accurate color gamut between different mastering monitors.
While REC.2020 refers to a wider color space that was standardized for UHD HDR video mastering, because most displays are still only capable of smaller gamut's than REC.2020, it is being used as a 'container' for smaller gamut's like P3-D65.
When the post production monitors are set to REC.2020, this requires a conversion to their native display primaries, and the methods for doing so can vary between monitors (gamut mapping vs. clipping, for example). For this reason, its most consistent and efficient to calibrate and encode using the P3-D65 colorspace. In that case, the studio will convert the content to BT.2020 later in their workflow.
But as you can see to the summary below, there studios where they used REC.2020 or custom gamut/colorspace coordinates also:
As for the most HDR10 titles currently available to the market, post production studios has been used the Sony BVM-X300 RGB OLED Reference Broadcast Monitor, as there unit-per-unit variations for luminance output capabilities and for gamut coverage also, these broadcast monitors are capable to reach up to ~1100 nits calibrated peak output, so some facilities are calibrating them for 1000 nits, while others for 1100 nits (like 20th Century Fox), for that reason there available a few titles mastered with 1100 nits ('Mastering Display Color Volume -> Maximum Display Luminance' value).
When we say '1000 nits monitor used', doesn't mean that the movie will have up to 1000 nits luminance levels, it can have much lower or much higher, as it's up to the colorist decision if he will 'hard clip' or leave un-clipped the content above 1000 nits, looking the waveform and RGB histogram of the content.
While tracking PQ-EOTF to the max nits of each LG 2019 OLED TV is capable to output; without using any tone-mapping but doing 'hard-clip'; is more accurate way to preserve the creative intent with a more authentic way, many users will prefer the tone-mapping capabilities which can offer a better picture for the average consumer eyes.