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Merge pull request #600 from njwardhan/feature/LUT-Improvements-GSoC
PR: Add "colour.models.rgb.transfer_functions.log" module.
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| Original file line number | Diff line number | Diff line change |
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| # | ||
| """ | ||
| Common Log Encodings | ||
| ==================== | ||
| Defines the common log encodings: | ||
| - :func:`colour.models.log_encoding_Log2` | ||
| - :func:`colour.models.log_decoding_Log2` | ||
| References | ||
| ---------- | ||
| - :cite:`TheAcademyofMotionPictureArtsandSciencesa` : | ||
| The Academy of Motion Picture Arts and Sciences, | ||
| Science and Technology Council, | ||
| & Academy Color Encoding System (ACES) Project Subcommittee.(n.d.-a). | ||
| ACESutil.Lin_to_Log2_param.ctl. Retrieved June 14, 2020, | ||
| from https://github.com/ampas/aces-dev/blob/\ | ||
| 518c27f577e99cdecfddf2ebcfaa53444b1f9343/transforms/ctl/utilities/ACESutil.Lin_to_Log2_param.ctl | ||
| - :cite:`TheAcademyofMotionPictureArtsandSciencesb` : | ||
| The Academy of Motion Picture Arts and Sciences, | ||
| Science and Technology Council, | ||
| & Academy Color Encoding System (ACES) Project Subcommittee.(n.d.-b). | ||
| ACESutil.Log2_to_Lin_param.ctl. Retrieved June 14, 2020, | ||
| from https://github.com/ampas/aces-dev/blob/\ | ||
| 518c27f577e99cdecfddf2ebcfaa53444b1f9343/transforms/ctl/utilities/ACESutil.Log2_to_Lin_param.ctl | ||
| """ | ||
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| from __future__ import division, unicode_literals | ||
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| import numpy as np | ||
| from colour.utilities import from_range_1, to_domain_1 | ||
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| __author__ = 'Colour Developers' | ||
| __copyright__ = 'Copyright (C) 2013-2020 - Colour Developers' | ||
| __license__ = 'New BSD License - https://opensource.org/licenses/BSD-3-Clause' | ||
| __maintainer__ = 'Colour Developers' | ||
| __email__ = 'colour-developers@colour-science.org' | ||
| __status__ = 'Production' | ||
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| __all__ = ['log_encoding_Log2', 'log_decoding_Log2'] | ||
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| def log_encoding_Log2(lin, | ||
| middle_grey=0.18, | ||
| min_exposure=0.18 * 2 ** -6.5, | ||
| max_exposure=0.18 * 2 ** 6.5): | ||
| """ | ||
| Defines the common *Log2* encoding function. | ||
| Parameters | ||
| ---------- | ||
| lin : numeric or array_like | ||
| Linear data to undergo encoding. | ||
| middle_grey : numeric, optional | ||
| *Middle Grey* exposure value. | ||
| min_exposure : numeric, optional | ||
| Minimum exposure level. | ||
| max_exposure : numeric, optional | ||
| Maximum exposure level. | ||
| Returns | ||
| ------- | ||
| numeric or ndarray | ||
| Non-linear *Log2* encoded data. | ||
| Notes | ||
| ----- | ||
| The common *Log2* encoding function can be used | ||
| to build linear to logarithmic shapers in the | ||
| ACES OCIO configuration. | ||
| A (48-nits OCIO) shaper having values in a linear | ||
| domain, can be encoded to a logarithmic domain: | ||
| +-------------------+-------------------+ | ||
| | **Shaper Domain** | **Shaper Range** | | ||
| +===================+===================+ | ||
| | [0.002, 16.291] | [0, 1] | | ||
| +-------------------+-------------------+ | ||
| References | ||
| ---------- | ||
| :cite:`TheAcademyofMotionPictureArtsandSciencesa` | ||
| Examples | ||
| -------- | ||
| Linear numeric input is encoded as follows: | ||
| >>> log_encoding_Log2(18) | ||
| 0.40773288970434662 | ||
| Linear array-like input is encoded as follows: | ||
| >>> log_encoding_Log2(np.linspace(1, 2, 3)) | ||
| array([ 0.15174832, 0.18765817, 0.21313661]) | ||
| """ | ||
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| lin = to_domain_1(lin) | ||
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| lg2 = np.log2(lin / middle_grey) | ||
| log_norm = (lg2 - min_exposure) / (max_exposure - min_exposure) | ||
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| return from_range_1(log_norm) | ||
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| def log_decoding_Log2(log_norm, | ||
| middle_grey=0.18, | ||
| min_exposure=0.18 * 2 ** -6.5, | ||
| max_exposure=0.18 * 2 ** 6.5): | ||
| """ | ||
| Defines the common *Log2* decoding function. | ||
| Parameters | ||
| ---------- | ||
| log_norm : numeric or array_like | ||
| Logarithmic data to undergo decoding. | ||
| middle_grey : numeric, optional | ||
| *Middle Grey* exposure value. | ||
| min_exposure : numeric, optional | ||
| Minimum exposure level. | ||
| max_exposure : numeric, optional | ||
| Maximum exposure level. | ||
| Returns | ||
| ------- | ||
| numeric or ndarray | ||
| Linear *Log2* decoded data. | ||
| Notes | ||
| ----- | ||
| The common *Log2* decoding function can be used | ||
| to build logarithmic to linear shapers in the | ||
| ACES OCIO configuration. | ||
| The shaper with logarithmic encoded values can be | ||
| decoded back to linear domain: | ||
| +-------------------+-------------------+ | ||
| | **Shaper Range** | **Shaper Domain** | | ||
| +===================+===================+ | ||
| | [0, 1] | [0.002, 16.291] | | ||
| +-------------------+-------------------+ | ||
| References | ||
| ---------- | ||
| :cite:`TheAcademyofMotionPictureArtsandSciencesb` | ||
| Examples | ||
| -------- | ||
| Logarithmic input is decoded as follows: | ||
| >>> log_decoding_Log2(0.40773288970434662) | ||
| 17.999999999999993 | ||
| Linear array-like input is encoded as follows: | ||
| >>> log_decoding_Log2(np.linspace(0, 1, 4)) | ||
| array([ 1.80248299e-01, 7.77032379e+00, 3.34970882e+02, | ||
| 1.44402595e+04]) | ||
| """ | ||
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| log_norm = to_domain_1(log_norm) | ||
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| lg2 = log_norm * (max_exposure - min_exposure) + min_exposure | ||
| lin = (2 ** lg2) * middle_grey | ||
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| return from_range_1(lin) |
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