Coverage for models/rgb/transfer_functions/filmlight_t_log.py: 65%
37 statements
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1"""
2FilmLight T-Log Log Encoding
3============================
5Define the *FilmLight T-Log* log encoding.
7- :func:`colour.models.log_encoding_FilmLightTLog`
8- :func:`colour.models.log_decoding_FilmLightTLog`
10References
11----------
12- :cite:`Siragusano2018a` : Siragusano, D. (2018). Private Discussion with
13 Shaw, Nick.
14"""
16from __future__ import annotations
18import numpy as np
20from colour.hints import ( # noqa: TC001
21 Domain1,
22 Range1,
23)
24from colour.utilities import as_float, from_range_1, to_domain_1
26__author__ = "Colour Developers"
27__copyright__ = "Copyright 2013 Colour Developers"
28__license__ = "BSD-3-Clause - https://opensource.org/licenses/BSD-3-Clause"
29__maintainer__ = "Colour Developers"
30__email__ = "colour-developers@colour-science.org"
31__status__ = "Production"
33__all__ = [
34 "log_encoding_FilmLightTLog",
35 "log_decoding_FilmLightTLog",
36]
39def log_encoding_FilmLightTLog(
40 x: Domain1,
41 w: float = 128.0,
42 g: float = 16.0,
43 o: float = 0.075,
44) -> Range1:
45 """
46 Apply the *FilmLight T-Log* log encoding opto-electronic transfer function (OETF).
48 Parameters
49 ----------
50 x
51 Linear reflection data :math:`x`.
52 w
53 Value of :math:`x` for which :math:`t = 1.0`.
54 g
55 Gradient at :math:`x = 0.0`.
56 o
57 Value of :math:`t` at :math:`x = 0.0`.
59 Returns
60 -------
61 :class:`numpy.ndarray`
62 *FilmLight T-Log* encoded data :math:`t`.
64 References
65 ----------
66 :cite:`Siragusano2018a`
68 Notes
69 -----
70 +------------+-----------------------+---------------+
71 | **Domain** | **Scale - Reference** | **Scale - 1** |
72 +============+=======================+===============+
73 | ``x`` | 1 | 1 |
74 +------------+-----------------------+---------------+
76 +------------+-----------------------+---------------+
77 | **Range** | **Scale - Reference** | **Scale - 1** |
78 +============+=======================+===============+
79 | ``t`` | 1 | 1 |
80 +------------+-----------------------+---------------+
82 - The following is an excerpt from the FilmLight colour space file
83 `./etc/colourspaces/FilmLight_TLog_EGamut.flspace` which can be
84 obtained by installing the free Baselight for Nuke plugin::
86 T-Log, a cineon driven log tone-curve developed by FilmLight.
87 The colour space is designed to be used as *Working Colour Space*.
89 Version 10.0
90 This is similar to Cineon LogC function.
92 The formula is...
93 y = A + B*log(x + C)
94 ...where x,y are the log and linear values.
96 A,B,C are constants calculated from...
97 w = x value for y = 1.0
98 g = the gradient at x=0
99 o = y value for x = 0.0
101 We do not have an exact solution but the
102 formula for b gives an approximation. The
103 gradient is not g, but should be within a
104 few percent for most sensible values of (w*g).
106 Examples
107 --------
108 >>> log_encoding_FilmLightTLog(0.18) # doctest: +ELLIPSIS
109 0.3965678...
110 """
112 x = to_domain_1(x)
114 b = 1 / (0.7107 + 1.2359 * np.log(w * g))
115 gs = g / (1 - o)
116 C = b / gs
117 a = 1 - b * np.log(w + C)
118 y0 = a + b * np.log(C)
119 s = (1 - o) / (1 - y0)
120 A = 1 + (a - 1) * s
121 B = b * s
122 G = gs * s
124 t = np.where(
125 x < 0.0,
126 G * x + o,
127 np.log(x + C) * B + A,
128 )
130 return as_float(from_range_1(t))
133def log_decoding_FilmLightTLog(
134 t: Domain1,
135 w: float = 128.0,
136 g: float = 16.0,
137 o: float = 0.075,
138) -> Range1:
139 """
140 Apply the *FilmLight T-Log* log decoding inverse opto-electronic transfer
142 function (OETF).
144 Parameters
145 ----------
146 t
147 *FilmLight T-Log* encoded data :math:`t`.
148 w
149 Value of :math:`x` for which :math:`t = 1.0`.
150 g
151 Gradient at :math:`x = 0.0`.
152 o
153 Value of :math:`t` at :math:`x = 0.0`.
155 Returns
156 -------
157 :class:`numpy.ndarray`
158 Linear reflection data :math:`x`.
160 References
161 ----------
162 :cite:`Siragusano2018a`
164 Notes
165 -----
166 +------------+-----------------------+---------------+
167 | **Domain** | **Scale - Reference** | **Scale - 1** |
168 +============+=======================+===============+
169 | ``t`` | 1 | 1 |
170 +------------+-----------------------+---------------+
172 +------------+-----------------------+---------------+
173 | **Range** | **Scale - Reference** | **Scale - 1** |
174 +============+=======================+===============+
175 | ``x`` | 1 | 1 |
176 +------------+-----------------------+---------------+
178 - The following is an excerpt from the FilmLight colour space file
179 `./etc/colourspaces/FilmLight_TLog_EGamut.flspace` which can be
180 obtained by installing the free Baselight for Nuke plugin::
182 T-Log, a cineon driven log tone-curve developed by FilmLight.
183 The colour space is designed to be used as *Working Colour Space*.
185 Version 10.0
186 This is similar to Cineon LogC function.
188 The formula is...
189 y = A + B*log(x + C)
190 ...where x,y are the log and linear values.
192 A,B,C are constants calculated from...
193 w = x value for y = 1.0
194 g = the gradient at x=0
195 o = y value for x = 0.0
197 We do not have an exact solution but the
198 formula for b gives an approximation. The
199 gradient is not g, but should be within a
200 few percent for most sensible values of (w*g).
202 Examples
203 --------
204 >>> log_decoding_FilmLightTLog(0.396567801298332) # doctest: +ELLIPSIS
205 0.1800000...
206 """
208 t = to_domain_1(t)
210 b = 1 / (0.7107 + 1.2359 * np.log(w * g))
211 gs = g / (1 - o)
212 C = b / gs
213 a = 1 - b * np.log(w + C)
214 y0 = a + b * np.log(C)
215 s = (1 - o) / (1 - y0)
216 A = 1 + (a - 1) * s
217 B = b * s
218 G = gs * s
220 x = np.where(
221 t < o,
222 (t - o) / G,
223 np.exp((t - A) / B) - C,
224 )
226 return as_float(from_range_1(x))