R: Opto-Optical Transfer Function, general

Opto-Optical Transfer Function, parameterized {spacesRGB}

R Documentation

Opto-Optical Transfer Function, general

Description

This parameterized OOTF maps from ACES (linear scene) RGB to linear display RGB (both of these are optical in nature).
This transform bypasses non-linear signal display RGB (which is electrical in nature).

Usage

general.OOTF( display_pri, Ymin=0.00010, Ymid=7.2, Ymax=108,
                 observerWP=NULL, limiting_pri=NULL,
                 surround='dark', dynrange='SDR', glowmod='1.1', redmod='1.1' )

Arguments

`display_pri`	a 4x2 matrix containing the display primaries, or a numeric vector of length 8 that can be converted to such a matrix, by row. Some built-in matrices are `REC709_PRI`, etc. This argument cannot be `NULL`.
`Ymin`	the minimum display luminance, in `cd/m^2`, or nit.
`Ymid`	the middle display luminance, in `cd/m^2`, or nit.
`Ymax`	the maximum display luminance, in `cd/m^2`, or nit.
`observerWP`	the xy chromaticity of the assumed observer whitepoint. This is used to make a Chromatic Adaptation Transform (CAT) from the ACES whitepoint (approximately D60) to the assumed observer whitepoint. If `observerWP` is `NULL`, it is taken from `display_pri`. If ACES and observer whitepoints are the same, there is no CAT.
`limiting_pri`	a 4x2 matrix containing the limiting primaries, or a numeric vector of length 8 that can be converted to such a matrix, by row. If `limiting_pri` is not `NULL`, and not equal to `display_pri`, then the output RGB is clamped to the RGB cube that corresponds to `limiting_pri`.
`surround`	The level of the surround luminance. Valid values are `'dark'` and `'dim'`. If the level is `'dark'` there is no special color compensation. Partial matching is enabled and matching is case-insensitive.
`dynrange`	the dynamic range of the display system. Valid values are `'SDR'` (standard dynamic range) and `'HDR'` (high dynamic range). If the value is `'HDR'` then `surround` is ignored. Matching is partial and case-insensitive.
`glowmod`	the version of the Glow Modifier to use. The only version currently supported is `"1.1"`. `glowmod` can also be `NULL`, `NA`, or `FALSE`, which means to use no Glow Modifier at all.
`redmod`	the version of the Red Modifier to use. The only version currently supported is `"1.1"`. This string can also be `"1.1+pinv"` which means to use a precision inverse; the forward transfer is exactly the same. This precision inverse uses an iterative root-finder, and is slower than the approximate default inverse. `redmod` can also be `NULL`, `NA`, or `FALSE`, which means to use no Red Modifier at all.

Details

The transfer is complicated; here is a summary of the steps:

glow module (see argument glowmod)
red modifier (see argument redmod)
matrix conversion from AP0 RGB → AP1 RGB
clamp to non-negative RGB
global desaturation (as in RRT.TF)
single-stage tone-scale (SSTS) using Ymin, Ymid, and Ymax
absolute luminance to linear code-value, in cube [0,1]^3
matrix conversion from AP1 RGB to XYZ
dim surround compensation (optional, see arguments surround and dynrange)
clamp XYZ to limiting primaries (optional, see argument limiting_pri)
adapt XYZ from ACES whitepoint to observer whitepoint (optional, see argument observerWP)
matrix conversion from XYZ to linear display RGB (see argument display_pri)
scale and roll-white to avoid clipping (optional, only when observerWP is ACES whitepoint and display whitepoint is D65 or DCI whitepoint)
clamp to non-negative RGB

Value

general.OOTF() returns a TransferFunction of dimension 3 that maps ACES RGB to linear display RGB.
The domain of the returned TransferFunction depends on the values of Ymin, Ymid, and Ymax. The range is [0,1]^3, for which clamping may be used.
The metadata contains the display primaries and whitepoint, which is useful in installRGB().

Source

This function was based on source code at: https://github.com/ampas/aces-dev; especially the file ACESlib.OutputTransforms.ctl. This transform is a sub-transform of the function outputTransform(); it omits the final EOTF^{-1} and optional Full-to-SMPTE range.

References

ST 2065-1:2012. SMPTE Standard - Academy Color Encoding Specification (ACES). 2013.