Source code for colour.models.rgb.transfer_functions.apple_log_profile
"""
Apple Log Profile Log Encoding
==============================
Define the *Apple Log Profile* log encoding.
- :func:`colour.models.log_encoding_AppleLogProfile`
- :func:`colour.models.log_decoding_AppleLogProfile`
References
----------
- :cite:`AppleInc.2023` : Apple Inc. (2023). Apple Log Profile White Paper.
https://developer.apple.com/download/all/?q=Apple%20log%20profile
- :cite:`TheAcademyofMotionPictureArtsandSciences2023` : The Academy of
Motion Picture Arts and Sciences. (2023). IDT.Apple.AppleLog_BT2020.ctl.
Retrieved December 17, 2023, from
https://github.com/ampas/aces-dev/blob/\
528c78fe2c0f4e7eb322581e98aba05de79466cb/transforms/ctl/idt/vendorSupplied/\
apple/IDT.Apple.AppleLog_BT2020.ctl
"""
from __future__ import annotations
import numpy as np
from colour.hints import ( # noqa: TC001
Domain1,
Range1,
)
from colour.utilities import Structure, as_float, from_range_1, optional, to_domain_1
__author__ = "Colour Developers"
__copyright__ = "Copyright 2013 Colour Developers"
__license__ = "BSD-3-Clause - https://opensource.org/licenses/BSD-3-Clause"
__maintainer__ = "Colour Developers"
__email__ = "colour-developers@colour-science.org"
__status__ = "Production"
__all__ = [
"CONSTANTS_APPLE_LOG_PROFILE",
"log_encoding_AppleLogProfile",
"log_decoding_AppleLogProfile",
]
CONSTANTS_APPLE_LOG_PROFILE: Structure = Structure(
R_0=-0.05641088,
R_t=0.01,
sigma=47.28711236,
beta=0.00964052,
gamma=0.08550479,
delta=0.69336945,
)
"""*Apple Log Profile* constants."""
[docs]
def log_encoding_AppleLogProfile(
R: Domain1,
constants: Structure | None = None,
) -> Range1:
"""
Apply the *Apple Log Profile* log encoding opto-electronic transfer function (OETF).
Parameters
----------
R
Linear reflection data :math:`R`.
constants
*Apple Log Profile* constants.
Returns
-------
:class:`numpy.ndarray`
Logarithmically encoded value :math:`P`.
References
----------
:cite:`AppleInc.2023`,
:cite:`TheAcademyofMotionPictureArtsandSciences2023`
Notes
-----
- The scene reflection signal :math:`R` captured by the camera is
represented using a floating point encoding. The :math:`R` value
of 0.18 corresponds to the signal produced by an 18% reflectance
reference gray chart.
+------------+-----------------------+---------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``R`` | 1 | 1 |
+------------+-----------------------+---------------+
+------------+-----------------------+---------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``P`` | 1 | 1 |
+------------+-----------------------+---------------+
Examples
--------
>>> log_encoding_AppleLogProfile(0.18) # doctest: +ELLIPSIS
np.float64(0.4882724...)
"""
R = to_domain_1(R)
constants = optional(constants, CONSTANTS_APPLE_LOG_PROFILE)
R_0 = constants.R_0
R_t = constants.R_t
sigma = constants.sigma
beta = constants.beta
gamma = constants.gamma
delta = constants.delta
P = np.select(
[
R >= R_t, # noqa: SIM300
np.logical_and(R_0 <= R, R < R_t), # noqa: SIM300
R < R_0,
],
[
gamma * np.log2(R + beta) + delta,
sigma * (R - R_0) ** 2,
0,
],
)
return as_float(from_range_1(P))
[docs]
def log_decoding_AppleLogProfile(
P: Domain1,
constants: Structure | None = None,
) -> Range1:
"""
Apply the *Apple Log Profile* log decoding inverse opto-electronic transfer
function (OETF).
Parameters
----------
P
Logarithmically encoded value :math:`P`.
constants
*Apple Log Profile* constants.
Returns
-------
:class:`numpy.ndarray`
Linear reflection data :math:`R`.
References
----------
:cite:`AppleInc.2023`,
:cite:`TheAcademyofMotionPictureArtsandSciences2023`
Notes
-----
- The captured pixel :math:`P` value uses floating point encoding
normalized to the [0, 1] range.
+------------+-----------------------+---------------+
| **Domain** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``P`` | 1 | 1 |
+------------+-----------------------+---------------+
+------------+-----------------------+---------------+
| **Range** | **Scale - Reference** | **Scale - 1** |
+============+=======================+===============+
| ``R`` | 1 | 1 |
+------------+-----------------------+---------------+
Examples
--------
>>> log_decoding_AppleLogProfile(0.48827245852686763) # doctest: +ELLIPSIS
np.float64(0.1800000...)
"""
P = to_domain_1(P)
constants = optional(constants, CONSTANTS_APPLE_LOG_PROFILE)
R_0 = constants.R_0
R_t = constants.R_t
sigma = constants.sigma
beta = constants.beta
gamma = constants.gamma
delta = constants.delta
P_t = sigma * (R_t - R_0) ** 2
R = np.select(
[
P >= P_t, # noqa: SIM300
np.logical_and(0 <= P, P < P_t), # noqa: SIM300
P < 0,
],
[
2 ** ((P - delta) / gamma) - beta,
np.sqrt(P / sigma) + R_0,
R_0,
],
)
return as_float(from_range_1(R))
