{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,4]],"date-time":"2026-06-04T21:10:20Z","timestamp":1780607420216,"version":"3.54.1"},"reference-count":51,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2019,3,4]],"date-time":"2019-03-04T00:00:00Z","timestamp":1551657600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Entropy"],"abstract":"<jats:p>Discrete entropy is used to measure the content of an image, where a higher value indicates an image with richer details. Infrared images are capable of revealing important hidden targets. The disadvantage of this type of image is that their low contrast and level of detail are not consistent with human visual perception. These problems can be caused by variations of the environment or by limitations of the cameras that capture the images. In this work we propose a method that improves the details of infrared images, increasing their entropy, preserving their natural appearance, and enhancing contrast. The proposed method extracts multiple features of brightness and darkness from the infrared image. This is done by means of the multiscale top-hat transform. To improve the infrared image, multiple scales are added to the bright areas and multiple areas of darkness are subtracted. The method was tested with 450 infrared thermal images from a public database. Evaluation of the experimental results shows that the proposed method improves the details of the image by increasing entropy, also preserving natural appearance and enhancing the contrast of infrared thermal images.<\/jats:p>","DOI":"10.3390\/e21030244","type":"journal-article","created":{"date-parts":[[2019,3,5]],"date-time":"2019-03-05T03:01:23Z","timestamp":1551754883000},"page":"244","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":77,"title":["Entropy and Contrast Enhancement of Infrared Thermal Images Using the Multiscale Top-Hat Transform"],"prefix":"10.3390","volume":"21","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3698-4043","authenticated-orcid":false,"given":"Julio C\u00e9sar","family":"Mello Rom\u00e1n","sequence":"first","affiliation":[{"name":"Facultad Polit\u00e9cnica, Universidad Nacional de Asunci\u00f3n, San Lorenzo 2160, Paraguay"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9766-4182","authenticated-orcid":false,"given":"Jos\u00e9 Luis","family":"V\u00e1zquez Noguera","sequence":"additional","affiliation":[{"name":"Facultad Polit\u00e9cnica, Universidad Nacional de Asunci\u00f3n, San Lorenzo 2160, Paraguay"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1790-2559","authenticated-orcid":false,"given":"Horacio","family":"Legal-Ayala","sequence":"additional","affiliation":[{"name":"Facultad Polit\u00e9cnica, Universidad Nacional de Asunci\u00f3n, San Lorenzo 2160, Paraguay"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2479-9876","authenticated-orcid":false,"given":"Diego P.","family":"Pinto-Roa","sequence":"additional","affiliation":[{"name":"Facultad Polit\u00e9cnica, Universidad Nacional de Asunci\u00f3n, San Lorenzo 2160, Paraguay"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Santiago","family":"Gomez-Guerrero","sequence":"additional","affiliation":[{"name":"Facultad Polit\u00e9cnica, Universidad Nacional de Asunci\u00f3n, San Lorenzo 2160, Paraguay"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6867-7080","authenticated-orcid":false,"given":"Miguel","family":"Garc\u00eda Torres","sequence":"additional","affiliation":[{"name":"Division of Computer Science, Universidad Pablo de Olavide, ES-41013 Seville, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2019,3,4]]},"reference":[{"key":"ref_1","unstructured":"Havens, K.J., and Sharp, E.J. (2016). Thermal Imaging Techniques to Survey and Monitor Animals in the Wild: A Methodology, Elsevier."},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Portmann, J., Lynen, S., Chli, M., and Siegwart, R. (June, January 31). People detection and tracking from aerial thermal views. Proceedings of the 2014 IEEE International Conference on Robotics and Automation (ICRA), Hong Kong, China.","DOI":"10.1109\/ICRA.2014.6907094"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"12296","DOI":"10.1364\/OE.15.012296","article-title":"Performance of infrared systems in swimmer detection for maritime security","volume":"15","author":"Krapels","year":"2007","journal-title":"Opt. Express"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"143","DOI":"10.1016\/j.infrared.2014.11.015","article-title":"Morphological infrared image enhancement based on multi-scale sequential toggle operator using opening and closing as primitives","volume":"68","author":"Bai","year":"2015","journal-title":"Infrared Phys. Technol."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"61","DOI":"10.1016\/j.infrared.2010.12.001","article-title":"Infrared image enhancement through contrast enhancement by using multiscale new top-hat transform","volume":"54","author":"Bai","year":"2011","journal-title":"Infrared Phys. Technol."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"309","DOI":"10.1016\/j.infrared.2012.03.004","article-title":"A new adaptive contrast enhancement algorithm for infrared images based on double plateaus histogram equalization","volume":"55","author":"Liang","year":"2012","journal-title":"Infrared Phys. Technol."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"84","DOI":"10.1016\/j.infrared.2011.01.001","article-title":"An approach to adaptive infrared image enhancement for long-range surveillance","volume":"54","author":"Lin","year":"2011","journal-title":"Infrared Phys. Technol."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"4283","DOI":"10.1016\/j.optcom.2010.06.072","article-title":"A quantitative measure based infrared image enhancement algorithm using plateau histogram","volume":"283","author":"Lai","year":"2010","journal-title":"Opt. Commun."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"99","DOI":"10.1016\/j.optlastec.2016.03.017","article-title":"Infrared image enhancement based on atmospheric scattering model and histogram equalization","volume":"83","author":"Li","year":"2016","journal-title":"Opt. Laser Technol."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Yoo, J.H., Ohm, S.Y., and Chung, M.G. (2012). Brightness Preservation and Image Enhancement Based on Maximum Entropy Distribution. Convergence and Hybrid Information Technology, Springer.","DOI":"10.1007\/978-3-642-32645-5_46"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"857","DOI":"10.1007\/s11760-016-1032-0","article-title":"Bi-histogram equalization using two plateau limits","volume":"11","author":"Ayala","year":"2017","journal-title":"Signal Image Video Process."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1109\/30.580378","article-title":"Contrast enhancement using brightness preserving bi-histogram equalization","volume":"43","author":"Kim","year":"1997","journal-title":"IEEE Trans. Consum. Electron."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"2072","DOI":"10.1109\/TCE.2009.5373771","article-title":"Bi-histogram equalization with a plateau limit for digital image enhancement","volume":"55","author":"Ooi","year":"2009","journal-title":"IEEE Trans. Consum. Electron."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"675","DOI":"10.1007\/s11760-013-0500-z","article-title":"A new histogram equalization method for digital image enhancement and brightness preservation","volume":"9","author":"Lim","year":"2013","journal-title":"Signal Image Video Process."},{"key":"ref_15","unstructured":"Pineda, I.A.B., Caballero, R.D.M., Silva, J.J.C., Rom\u00e1n, J.C.M., and Noguera, J.L.V. (2019). Quadri-histogram equalization using cutoff limits based on the size of each histogram with preservation of average brightness. Signal Image Video Process."},{"key":"ref_16","unstructured":"Rom\u00e1n, J.C.M., Ayala, H.L., and Noguera, J.L.V. (2017, January 17\u201320). Top-Hat transform for enhancement of aerial thermal images. Proceedings of the 2017 30th SIBGRAPI Conference on Graphics, Patterns and Images (SIBGRAPI), Niteroi, Brazil."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Sun, K., and Sang, N. (2007, January 6\u20138). Enhancement of vascular angiogram by multiscale morphology. Proceedings of the 1st International Conference on Bioinformatics and Biomedical Engineering (ICBBE 2007), Wuhan, China.","DOI":"10.1109\/ICBBE.2007.338"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"4678","DOI":"10.1364\/AO.54.004678","article-title":"Microscopy mineral image enhancement through center operator construction","volume":"54","author":"Bai","year":"2015","journal-title":"Appl. Opt."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"338","DOI":"10.1364\/AO.51.000338","article-title":"Noise-suppressed image enhancement using multiscale top-hat selection transform through region extraction","volume":"51","author":"Bai","year":"2012","journal-title":"Appl. Opt."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"44","DOI":"10.1016\/j.infrared.2016.11.011","article-title":"Edge enhanced morphology for infrared image analysis","volume":"80","author":"Bai","year":"2017","journal-title":"Infrared Phys. Technol."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"2145","DOI":"10.1016\/j.patcog.2009.12.023","article-title":"Analysis of new top-hat transformation and the application for infrared dim small target detection","volume":"43","author":"Bai","year":"2010","journal-title":"Pattern Recognit."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"177","DOI":"10.1016\/j.infrared.2011.12.002","article-title":"Infrared dim small target enhancement using toggle contrast operator","volume":"55","author":"Bai","year":"2012","journal-title":"Infrared Phys. Technol."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"2999","DOI":"10.1016\/j.sigpro.2010.04.021","article-title":"Analysis of different modified top-hat transformations based on structuring element construction","volume":"90","author":"Bai","year":"2010","journal-title":"Signal Process."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1196","DOI":"10.1016\/j.compeleceng.2011.08.010","article-title":"Toggle and top-hat based morphological contrast operators","volume":"38","author":"Bai","year":"2012","journal-title":"Comput. Electr. Eng."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"2004","DOI":"10.1016\/j.optlastec.2012.03.039","article-title":"Multi-scale toggle operator for constructing image sharpness measure","volume":"44","author":"Bai","year":"2012","journal-title":"Opt. Laser Technol."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"685","DOI":"10.1016\/S0165-1684(99)00161-9","article-title":"A multiscale morphological approach to local contrast enhancement","volume":"80","author":"Mukhopadhyay","year":"2000","journal-title":"Signal Process."},{"key":"ref_27","unstructured":"Gonzalez, R.C., Woods, R.E., and Eddins, S.L. (2004). Digital Image Processing Using MATLAB, Pearson-Prentice-Hall."},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Soille, P. (2004). Morphological Image Analysis: Principles and Applications, Springer.","DOI":"10.1007\/978-3-662-05088-0"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1614","DOI":"10.1016\/j.ijleo.2012.06.016","article-title":"A unified form of multi-scale top-hat transform based algorithms for image processing","volume":"124","author":"Bai","year":"2013","journal-title":"Optik"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"328","DOI":"10.1016\/j.optlastec.2011.07.009","article-title":"Image enhancement using multi scale image features extracted by top-hat transform","volume":"44","author":"Bai","year":"2012","journal-title":"Opt. Laser Technol."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"56","DOI":"10.1016\/j.optlastec.2013.10.018","article-title":"Retinal vessel enhancement based on multi-scale top-hat transformation and histogram fitting stretching","volume":"58","author":"Liao","year":"2014","journal-title":"Opt. Laser Technol."},{"key":"ref_32","doi-asserted-by":"crossref","unstructured":"Peng, B., Wang, Y., and Yang, X. (2010, January 17\u201319). A multiscale morphological approach to local contrast enhancement for ultrasound images. Proceedings of the 2010 International Conference on Computational and Information Sciences, Chengdu, China.","DOI":"10.1109\/ICCIS.2010.282"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"4421","DOI":"10.1016\/j.ijleo.2013.01.100","article-title":"Image enhancement through contrast enlargement using the image regions extracted by multiscale top-hat by reconstruction","volume":"124","author":"Bai","year":"2013","journal-title":"Optik"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"3198","DOI":"10.1016\/j.ijleo.2012.09.054","article-title":"Image fusion through local feature extraction by using multi-scale top-hat by reconstruction operators","volume":"124","author":"Bai","year":"2013","journal-title":"Optik"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"93","DOI":"10.1016\/j.infrared.2012.11.003","article-title":"Fusion of visible and infrared images using saliency analysis and detail preserving based image decomposition","volume":"56","author":"Zhao","year":"2013","journal-title":"Infrared Phys. Technol."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"139","DOI":"10.1016\/j.optlastec.2017.07.054","article-title":"Fusion of infrared polarization and intensity images based on improved toggle operator","volume":"98","author":"Zhu","year":"2018","journal-title":"Opt. Laser Technol."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"533","DOI":"10.1109\/TIP.2003.810757","article-title":"Multiscale morphological segmentation of gray-scale images","volume":"12","author":"Mukhopadhyay","year":"2003","journal-title":"IEEE Trans. Image Process."},{"key":"ref_38","first-page":"638","article-title":"Small target detection method based on morphology top-hat operator","volume":"7","author":"Ye","year":"2002","journal-title":"J. Image Graph."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"338","DOI":"10.1007\/s10278-007-9044-5","article-title":"Information entropy measure for evaluation of image quality","volume":"21","author":"Tsai","year":"2008","journal-title":"J. Dig. Imaging"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"10","DOI":"10.1016\/j.patrec.2013.08.024","article-title":"Image enhancement using exposure based sub image histogram equalization","volume":"36","author":"Singh","year":"2014","journal-title":"Pattern Recognit. Lett."},{"key":"ref_41","unstructured":"Ye, Z., Mohamadian, H., Pang, S.S., and Iyengar, S. (2007, January 14\u201316). Image contrast enhancement and quantitative measuring of information flow. Proceedings of the 6th WSEAS International Conference on Information Security and Privacy, Tenerife, Spain."},{"key":"ref_42","doi-asserted-by":"crossref","unstructured":"More, L.G., Brizuela, M.A., Ayala, H.L., Pinto-Roa, D.P., and Noguera, J.L.V. (2015, January 27\u201330). Parameter tuning of CLAHE based on multi-objective optimization to achieve different contrast levels in medical images. Proceedings of the 2015 IEEE International Conference on Image Processing (ICIP), Quebec City, QC, Canada.","DOI":"10.1109\/ICIP.2015.7351687"},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"589","DOI":"10.1109\/42.108593","article-title":"Entropic contrast enhancement","volume":"10","author":"Khellaf","year":"1991","journal-title":"IEEE Trans. Med. Imaging"},{"key":"ref_44","doi-asserted-by":"crossref","unstructured":"Wang, S.H., Cheng, H., Phillips, P., and Zhang, Y.D. (2018). Multiple Sclerosis Identification Based on Fractional Fourier Entropy and a Modified Jaya Algorithm. Entropy, 20.","DOI":"10.3390\/e20040254"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"873","DOI":"10.1177\/0037549716667834","article-title":"Smart detection on abnormal breasts in digital mammography based on contrast-limited adaptive histogram equalization and chaotic adaptive real-coded biogeography-based optimization","volume":"92","author":"Zhang","year":"2016","journal-title":"Simulation"},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"2015","DOI":"10.1109\/TCSVT.2015.2477915","article-title":"A new framework for measuring 2D and 3D visual information in terms of entropy","volume":"26","author":"Lee","year":"2016","journal-title":"IEEE Trans. Circuits Syst. Video Technol."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"379","DOI":"10.1002\/j.1538-7305.1948.tb01338.x","article-title":"A mathematical theory of communication","volume":"27","author":"Shannon","year":"1948","journal-title":"Bell Syst. Tech. J."},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"4815","DOI":"10.1109\/TIP.2016.2598485","article-title":"Image enhancement by entropy maximization and quantization resolution upconversion","volume":"25","author":"Niu","year":"2016","journal-title":"IEEE Trans. Image Process."},{"key":"ref_49","doi-asserted-by":"crossref","unstructured":"Burger, W., and Burge, M.J. (2016). Digital Image Processing: An Algorithmic Introduction Using Java, Springer.","DOI":"10.1007\/978-1-4471-6684-9"},{"key":"ref_50","unstructured":"Dataset (2018, December 01). Thermal Infrared Dataset. Available online: https:\/\/projects.asl.ethz.ch\/datasets\/doku.php?id=ir:iricra2014."},{"key":"ref_51","doi-asserted-by":"crossref","unstructured":"Zuiderveld, K. (1994). Contrast limited adaptive histogram equalization. Graphics Gems, Elsevier.","DOI":"10.1016\/B978-0-12-336156-1.50061-6"}],"container-title":["Entropy"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1099-4300\/21\/3\/244\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T12:36:10Z","timestamp":1760186170000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1099-4300\/21\/3\/244"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,3,4]]},"references-count":51,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2019,3]]}},"alternative-id":["e21030244"],"URL":"https:\/\/doi.org\/10.3390\/e21030244","relation":{},"ISSN":["1099-4300"],"issn-type":[{"value":"1099-4300","type":"electronic"}],"subject":[],"published":{"date-parts":[[2019,3,4]]}}}