ColorBox In-Line Color and HDR/SDR Transform v1.0 39 www.aja.com
BBC HLG LUT Name, Number
Description
HLG > SDR Display, #8c
BT.2100 HLG signals are down-mapped (tone-mapped) to BT.709 using a display-
light conversion. Colors and the appearance of mid-tones and lowlights are
maintained after conversion. The LUT, therefore, attempts to preserve the artistic
intent of the original HLG content. This LUT is designed to complement LUT 5
(BT.709 to BT.2100 HLG up-mapping) so that the losses associated with ‘round-
tripping’ (i.e. SDR-to-HDR-to-SDR conversion) are minimized. “HDR Reference
White” (75% HLG) is tone-mapped to 87% BT.709, facilitating signal headroom for
compressed highlights. 100% HLG signal is tone-mapped to 100% BT.709. With Type
III LUTs that process sub-blacks and super-whites, the HLG super-white signals are
tone-mapped to SDR super-white signals. The LUT outputs are clipped to EBU R.103
signal levels. The 3D-LUT interpolation errors are greatest for the HDR to SDR down-
mapping LUTs, as the output signals reach the extremities of the RGB signal range.
For that reason, in addition to the “ideal” output values for the EBU Tech 3373 HLG
Color Bars, we also provide the expected output values from a trilinear interpolator.
Errors should be smaller with tetrahedral interpolation, the 65-cubed LUTs and also
with real pictures.
NOTE: Neither the EBU Tech 3373 HLG color bars nor the ITU-R BT.2111 HLG color
bars will look like standard BT.709 color bars after conversion, as the BT.2100 color-
primaries are quite different to those of BT.709. Furthermore, the converted color
bars will not look like BT.2111 color bars displayed on a current reference display
as their color-primaries tend to be closer to DCI-P3 than BT.2100. Most noticeable
might be the BT.2100 green, which is much more cyan in color than the DCI-P3 and
BT.709 greens.
HLG > SDR Display Super, #9c
BT.2100 HLG signals are down-mapped (tone-mapped) to BT.709 using a display-
light conversion. Colors and the appearance of mid-tones and lowlights are
maintained after conversion. The LUT, therefore, attempts to preserve the artistic
intent of the original HLG content. “HDR Reference White” (75% HLG) is mapped to
95% BT.709 and HDR highlights extend into the SDR super-white region; for that
reason, only “Full-Range Mode” Type III LUTs are made available. 100% HLG signal
is mapped to the EBU R103 preferred maximum of 105% BT.709. HLG signals above
100% are clipped. This LUT is recommended for use in scenarios where minimizing
SDR>HDR>SDR “round-trip” losses is of the utmost importance. Minimal round-trip
losses are achieved when used with the display-light up-mapping LUT5. Where
the program delivery and distribution chain preserves the SDR super-white signal
range, this LUT9 usually gives better results than LUT8 as its output color volume
is larger. Where there is a risk of the SDR super-white signal range being clipped,
LUT8 should be used instead. The 3D-LUT interpolation errors are greatest for the
HDR to SDR down-mapping LUTs, as the output signals reach the extremities of the
RGB signal range. For that reason, in addition to the “ideal” output values for the
EBU Tech 3373 HLG Color Bars, we also provide the expected output values from
a trilinear interpolator. Errors should be smaller with tetrahedral interpolation, the
65-cubed LUTs and also with real pictures.
NOTE: Neither the EBU Tech 3373 HLG color bars nor the ITU-R BT.2111 HLG color
bars will look like standard BT.709 color bars after conversion, as the BT.2100 color
primaries are quite different from those of BT.709. Furthermore, the converted color
bars will not look like BT.2111 color bars displayed on a current reference display, as
their color primaries tend to be closer to DCI-P3 than BT.2100. Of these, the most
noticeable might be the BT.2100 green. This contains more cyan content than the
DCI-P3 and BT.709 greens.
HLG > PQ 1000 Nits Display, #7c
BT.2100 HLG signals are converted to BT.2100 PQ at the 1000 cd/m2 “bridge”
condition, so that 100% HLG maps to 1000 cd/m2 PQ. See ITU-R report BT.2390
Section 7.2 (“Conversion concepts using a reference condition at 1000 cd/m2”). For
Type III LUTs, HLG signals above 100% are mapped to PQ signals greater than 1000
cd/m2, up to a maximum of 1810 cd/m2 (corresponding to 109% HLG ‘super-white’,
i.e. 10-bit code value 1019).