ColorBox In-Line Color and HDR/SDR Transform v1.0 38 www.aja.com
BBC HLG LUT Name, Number
Description
S-Log3 200% Scene > HLG, #11a
For use with Sony S-Log3 cameras in “SR Live” workflows. S-Log3 (BT.2020 color)
signals produced using Sony’s “SR Live” “200%” workflow (i.e. 200% IRE input equals
90% reflectance) are converted to BT.2100 HLG with ITU-R BT.2408 signal levels. A
200% IRE input signal (90% reflectance) thus maps to 73% HLG. 200% workflows
are commonly encountered whenever the S-Log3 curve has been used in live
productions. A scene-light conversion is used, so that the converted S-Log3 signal
matches the “look” of BT.2100 HLG cameras.
Table 3. BBC HLG LUT Convert From HLG, Detailed Information
BBC HLG LUT Name, Number
Description
HLG > SDR Scene , #12-1c
For matching downstream SDR cameras that approximate the BT.709 OETF with
a square root function. BT.2100 HLG signals are down-mapped (tone-mapped) to
BT.709, using scene-light conversion. The “look” of the original BT.2100 HLG content
is changed to match “native” BT.709 cameras with a square-root approximation
of the BT.709 OETF. This LUT is the exact inverse of LUT 6-1 (BT.709 to BT.2100
up-mapping, scene-light), so that the losses associated with ‘roundtripping’ (i.e.
SDR-to-HDR-to-SDR conversion) are minimized. “HDR Reference White” (75% HLG)
is tone-mapped to 95% BT.709, allowing for some soft-clipping of highlights. A 79%
HLG signal is tone-mapped to 100% BT.709. With Type III LUTs that process sub-
blacks and super-whites, 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.
HLG > SDR Scene Strict, #12-2c
For use with SDR cameras that implement a strict BT.709 OETF. BT.2100 HLG signals
are down-mapped (tone-mapped) to BT.709, using a scene-light conversion. The
“look” of the original BT.2100 HLG content is changed to match “native” BT.709
cameras, with a strict implementation of the BT.709 OETF. This LUT is the exact
inverse of LUT6-2 (BT.709 to BT.2100 HLG inverse tone-mapping, scene-light), 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 95% BT.709,
allowing for some soft-clipping of highlights. 79% HLG signal is tone-mapped to
100% BT.709. With Type III LUTs that process sub-blacks and super-whites, the LUT
outputs are clipped to EBU R.103 signal levels.
NOTE: Unlike BT.2100 HLG, SDR cameras that implement a strict BT.709 OETF tend
to crush detail in the shadows of a scene. Shadow-detail visible in the HDR image
will, as a result, become less evident after applying this conversion. 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.