PQ HDR Add OOTF (Add Contrast) v1.0
PQ HDR Add OOTF (Add Contrast) v1.0
The MBOX PQ HDR Add OOTF (Add Contrast) LUTs are designed to compensate for the fact that the PQ HDR Transfer Function doesn't automatically include a system gamma or non-linear OOTF.
There are 42 LUTs in this LUT pack:
12 x Add OOTF to PQ Fixed at 100 Nits (Gammas 0.90 to 1.40 [1.00 excluded] in 0.05 increments, 1.50 & 1.60)
12 x Add OOTF to PQ Fixed at 1,000 Nits (Gammas 0.90 to 1.40 [1.00 excluded] in 0.05 increments, 1.50 & 1.60)
12 x Add OOTF to PQ Fixed at 10,000 Nits (Gammas 0.90 to 1.40 [1.00 excluded] in 0.05 increments, 1.50 & 1.60)
3 x Linear to PQ LUTs, Fixed with 100, 1,000, and 10,000 nits reference values
3 x PQ to Linear LUTs, fixed with 100, 1,000, and 10,000 nits reference values
Standard Dynamic Range used a Camera OETF gamma of 1/2.2 (about 0.45), while SDR displays used an EOTF of 2.4. The relationship between the camera gamma and the display gamma is called the system gamma, or OOTF; and in the case of SDR video, the system gamma is 1/2.2 * 2.4 = 1.09.
A system gamma of 1.09 means that for every 1 stop of dynamic range captured by the camera, the display reproduces it using 1.09 stops of brightness. This adds a small amount of contrast to the image, which we call "standard contrast".
Without standard contrast, an image appears washed out or flat. While HLG HDR applies a system gamma at the display to any image data encoded in the HLG OETF, Perceptual Quantization HDR does not. Its encoding is absolute.
As a result, mathematically moving from a Camera RAW or LOG format into PQ requires the addition of contrast.
The LUTs in this LUT pack are designed to add an OOTF to log footage directly translated into PQ HDR. Each LUT has two values: the Nits value the image data is held in place at, and a stretch factor (system gamma, or OOTF). The higher the OOTF value, the higher the applied contrast.
The Nits value defines which values are stretched upwards and which are stretched downwards. For instance, when the OOTF is fixed at 1000 nits, every value below 1000 nits brightness is pulled downward as the contrast is applied, and every value above 1000 nits is pulled upwards. As such, fixing at 100 nits is the most common fixed value, since it matches about 2-3 stops above the camera's reference exposure.
The higher dynamic range of HDR video, and the larger display sizes, means that a system gamma of about 1.2 is perceived to be a similar contrast factor as SDR's SG 1.09.
These LUTs may be combined with Mystery Box's Camera LOG to PQ HDR LUTs, to add additional contrast, or combined together for further extended or contracted system gamma ranges. When combining OOTF LUTs, the resulting system gamma / OOTF / stretch factor is the multiplied result of the two combined OOTFs. For instance, if I add both an OOTF of 1.2 and an OOTF of 1.4, my resulting OOTF is 1.2 * 1.4 = 1.68.
When combining with the MBOX Camera LOG to PQ HDR LUTs, the natural language contrast declarations equate to the following OOTFs:
Low Contrast: 1.0
Standard Contrast: 1.09
Medium Contrast: 1.2
High Contrast: 1.35
Very High Contrast: 1.6
For more information regarding system gammas, stretch factors, and contrast in HDR, please see http://mysterybox.us/blog-home/ (specific posts coming soon).
These LUTs are licensed for use in a post-production setting for applying to assets prior to the assets distribution. If you are interested in incorporating these LUTs into HDR encoding, distribution, or exhibition technology, please contact us for more information on licensing.