- License Notice
- Image Credits
- Sample Images (Detailed Attribution)
- Image Processing Methods and Techniques
- CROW Software
- Academic Use
Important: The CROW software (source code) is licensed under the CC BY-NC-SA 4.0 (Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International). However, the sample images in the input/ directory have their own individual licenses as specified below. These images are provided as examples only and are not covered by the software license.
What this means:
- The software is free for non-commercial use (personal, educational, research)
- Commercial use requires permission from the author
- Any modifications must be shared under the same license
- Attribution to Robin Molnar is required
If you redistribute CROW, you must respect both the software license and the individual licenses of any sample images you include.
Sample images used in this repository are credited below with their full license information:
- input/1.jpeg - By Ian Kirk, licensed under CC BY 2.0 from Wikimedia Commons
- input/2.jpeg - By Alexis Lours, licensed under CC BY 4.0 from Wikimedia Commons
- input/3.jpeg - "Lilith" by DrL, licensed under CC BY-SA 2.5 from Wikimedia Commons
- input/4.jpeg - By GALAXY 2018 A7, released into Public Domain (CC0 1.0)
- input/5.jpeg - By Lotusgreen, licensed under CC BY-SA 4.0 from Wikimedia Commons
- input/6.jpeg - By Amcyrus2012, licensed under CC BY 4.0 from Wikimedia Commons
- input/7.jpeg - By Evan-Amos, released into Public Domain
Thank you to all photographers who share their work under open licenses!
Source: Wikimedia Commons
Author: Ian Kirk from Broadstone, Dorset, UK
License: CC BY 2.0 (Creative Commons Attribution 2.0 Generic)
Wikipedia Article: https://en.wikipedia.org/wiki/Crow
Commons File: File:Corvus corone -near Canford Cliffs, Poole, England-8.jpg
Description: A carrion crow scavenging on the beach near Canford Cliffs, Poole, Dorset, England
Date Created: 8 February 2014
Location: 50° 41′ 38.78″ N, 1° 55′ 56.22″ W
This image is licensed under the Creative Commons Attribution 2.0 Generic license. You are free to:
- Share — copy and redistribute the material in any medium or format
- Adapt — remix, transform, and build upon the material for any purpose, even commercially
Under the following terms:
- Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made.
Full license text: https://creativecommons.org/licenses/by/2.0/
Source: Wikimedia Commons
Author: Alexis Lours
License: CC BY 4.0 (Creative Commons Attribution 4.0 International)
Wikipedia Article: https://en.wikipedia.org/wiki/Carrion_crow
Image URL: https://en.wikipedia.org/wiki/Carrion_crow#/media/File:Carrion_crow_2022_04_05_05_02.jpg
Commons URL: https://commons.wikimedia.org/w/index.php?curid=119074860
Description: Carrion crow image used as sample for demonstrating CROW color enhancement
This image is licensed under the Creative Commons Attribution 4.0 International license. You are free to:
- Share — copy and redistribute the material in any medium or format
- Adapt — remix, transform, and build upon the material for any purpose, even commercially
Under the following terms:
- Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made.
Full license text: https://creativecommons.org/licenses/by/4.0/
Source: Wikimedia Commons
Author: DrL (original uploader at English Wikipedia)
License: CC BY-SA 2.5 (Creative Commons Attribution-ShareAlike 2.5 Generic)
Wikipedia Article: https://en.wikipedia.org/wiki/Black_cat
Image URL: https://en.wikipedia.org/wiki/Black_cat#/media/File:Blackcat-Lilith.jpg
Commons File: File:Blackcat-Lilith.jpg
Description: A black cat named Lilith resting on a fence, found as a kitten in a supermarket parking lot
Date Created: 15 August 2006
Date Uploaded: 14 June 2007
Note: Original author requests keeping "Lilith" in the file name when sharing
This image is licensed under the Creative Commons Attribution-ShareAlike 2.5 Generic license. You are free to:
- Share — copy, distribute and transmit the work
- Remix — adapt the work
Under the following conditions:
- Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
- Share Alike — If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.
Full license text: https://creativecommons.org/licenses/by-sa/2.5/
Source: Wikimedia Commons
Author: GALAXY 2018 A7
License: CC0 1.0 Universal (Public Domain Dedication)
Wikipedia Article: https://en.wikipedia.org/wiki/Bark_(botany)
#/media/File:Poskozena_borka_na_tresni_20210821_150436.jpg){kind=link}
Commons File: File:Poskozena borka na tresni 20210821 150436.jpg
Description: Damaged bark of a cherry tree, painted over but the tree was able to restore it (Poškozená borka na třešni - zatřena barvou, ale strom byl schopen ji obnovit)
Date Created: 21 August 2021
Date Uploaded: 21 August 2021
This work has been released into the public domain by its author, GALAXY 2018 A7, using the CC0 1.0 Universal Public Domain Dedication.
This means:
- No Rights Reserved - The person who associated a work with this deed has dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
- You can copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission.
- No attribution is required, but attribution is appreciated.
Full license text: https://creativecommons.org/publicdomain/zero/1.0/
Source: Wikimedia Commons
Author: Lotusgreen
License: CC BY-SA 4.0 (Creative Commons Attribution-ShareAlike 4.0 International)
Wikipedia Article: https://en.wikipedia.org/wiki/Bark_(botany)
#/media/File:Chinese_Evergreen_Elm_after_Yellow-Bellied_Sapsucker,_February_2012.jpg){kind=link}
Commons File: File:Chinese Evergreen Elm after Yellow-Bellied Sapsucker, February 2012.jpg
Description: The patterns left in the bark of a Chinese Evergreen Elm after repeated visits by a Yellow-Bellied Sapsucker (woodpecker) in early 2012
Date Created: 24 July 2014
Date Uploaded: 25 July 2014
This image is licensed under the Creative Commons Attribution-ShareAlike 4.0 International license. You are free to:
- Share — copy and redistribute the material in any medium or format
- Adapt — remix, transform, and build upon the material for any purpose, even commercially
Under the following conditions:
- Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
- Share Alike — If you remix, transform, or build upon the material, you must distribute your contributions under the same or compatible license as the original.
Full license text: https://creativecommons.org/licenses/by-sa/4.0/
Source: Wikimedia Commons
Author: Amcyrus2012
License: CC BY 4.0 (Creative Commons Attribution 4.0 International)
Wikipedia Article: https://en.wikipedia.org/wiki/Coal
Image URL: https://en.wikipedia.org/wiki/Coal#/media/File:Bituminous_Coal.JPG
Commons File: File:Bituminous Coal.JPG
Description: Bituminous Coal
Date Created: 7 January 2015
Date Uploaded: 7 January 2015
This image is licensed under the Creative Commons Attribution 4.0 International license. You are free to:
- Share — copy and redistribute the material in any medium or format
- Adapt — remix, transform, and build upon the material for any purpose, even commercially
Under the following terms:
- Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made.
Full license text: https://creativecommons.org/licenses/by/4.0/
Source: Wikimedia Commons
Author: Evan-Amos
License: Public Domain Dedication (Released to Public Domain worldwide)
Wikipedia Article: https://ro.wikipedia.org/wiki/Fontă (Romanian Wikipedia - Cast Iron)
Image URL: https://ro.wikipedia.org/wiki/Fontă#/media/Fișier:Cast-Iron-Pan.jpg
Commons File: File:Cast-Iron-Pan.jpg
Description: A cast-iron pan (O tigaie fabricată din fontă)
Date Created: 29 October 2010
Date Uploaded: 4 November 2010
This work has been released into the public domain worldwide by its author, Evan-Amos.
This means:
- No Rights Reserved - The copyright holder has released this work to the public domain by waiving all rights to the work worldwide under copyright law, including all related and neighboring rights.
- You can copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission.
- No attribution is required, though attribution is appreciated.
- This dedication is valid worldwide, with no conditions unless required by law.
Note: In some countries this may not be legally possible; if so, the author grants anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.
CROW uses several established image processing algorithms and color space transformations:
HSV (Hue, Saturation, Value)
- Used in Methods 1 and 5 for color manipulation
- Reference: OpenCV Documentation - Color Space Conversions
Lab Color Space (CIELAB)
- Used in Method 2 for perceptually uniform color enhancement
- Based on CIE 1976 Lab* color space
- Reference: CIE Color Space
- Smith, A. R. (1978). "Color Gamut Transform Pairs". SIGGRAPH '78 Proceedings
Method 3: Multi-Scale Retinex
- Based on the Retinex theory of color constancy
- Reference: Jobson, D. J., Rahman, Z., & Woodell, G. A. (1997). "A multiscale retinex for bridging the gap between color images and the human observation of scenes". IEEE Transactions on Image Processing, 6(7), 965-976.
- Paper: https://ieeexplore.ieee.org/document/597272
- Land, E. H., & McCann, J. J. (1971). "Lightness and retinex theory". Journal of the Optical Society of America, 61(1), 1-11.
Canny Edge Detection
- Used in Method 5 for structure-preserving color enhancement
- Reference: Canny, J. (1986). "A Computational Approach to Edge Detection". IEEE Transactions on Pattern Analysis and Machine Intelligence, PAMI-8(6), 679-698.
- Paper: https://ieeexplore.ieee.org/document/4767851
Morphological Image Processing
- Used for bird mask detection and refinement
- Operations: erosion, dilation, opening, closing
- Reference: Haralick, R. M., Sternberg, S. R., & Zhuang, X. (1987). "Image Analysis Using Mathematical Morphology". IEEE Transactions on Pattern Analysis and Machine Intelligence, PAMI-9(4), 532-550.
- OpenCV Documentation: Morphological Transformations
OpenCV (Open Source Computer Vision Library)
- Primary library for image processing operations
- Website: https://opencv.org/
- License: Apache 2.0 License
- Bradski, G. (2000). "The OpenCV Library". Dr. Dobb's Journal of Software Tools.
NumPy
- Numerical computing library for array operations
- Website: https://numpy.org/
- License: BSD License
- Harris, C.R., Millman, K.J., van der Walt, S.J. et al. (2020). "Array programming with NumPy". Nature 585, 357–362.
Author: Robin Molnar
GitHub: @robintel
LinkedIn: robintel
License: CC BY-NC-SA 4.0 (Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International)
Repository: https://github.com/robintel/crow
Copyright: © 2025 Robin Molnar
For commercial licensing inquiries, please contact the author through GitHub or LinkedIn.
If you use CROW in academic research or publications, please consider citing:
Molnar, R. (2025). CROW - Color Reveal Of Wings: A Multi-Method Approach
to Revealing Iridescent Colors in Bird Feathers.
GitHub repository: https://github.com/robintel/crow
And acknowledge the underlying algorithms referenced above as appropriate for your work.
If you use CROW in your research or projects, please consider citing this repository and acknowledging the sample image authors.