Image Enhancement

Color can deeply change its characteristics when put and analyzed into its spatial context. This consideration has originated a group of algorithms which aim to change a point according to the whole scene in which the point is observed. The term used to refer to these algorithms is "Spatial Color Algorithms" (SCAs). In the last years, we proposed several SCAs, based or inspired by Retinex theory of color vision: Brownian Retinex, ACE, RSR, RACE, STRESS.

Spatial Color Algorithms (SCAs)

The term “Spatial Color” refers to a family of algorithms that recompute wavelength/energy arrays into calculated color appearance arrays, or preferred color enhancement arrays, according to the spatial distribution of pixel values in the scene. They can be used for modeling HVS or simply for unsupervised image enhancement.
The starting algorithm of this family is Retinex.
The idea at the base of Retinex, a contraction of the words retina and cortex, is that these two parts of human body, which compose our vision system, realize a robust adjustment to compensate for the high photometric and colorimetric variability of the world around us. This is realized by spatial comparisons within the various areas of the visual input. Such comparisons are modeled as a series of ratios and multiplications among near and far areas. At the base of Retinex computation is the idea, presented above, of performing spatial comparisons among areas of the visual input (image) and computing a chain of ratio-product reset. The ratio-product reset mechanism is also the common core of the Milano-Retinex family, a variant developed at the Università degli Studi di Milano

Fast ACE (FACE)

We have just published the paper "Fast ACE (FACE): An Error-Bounded Approximation of Automatic Color Equalization" in IEEE Transactions on Image Processing, vol. 32, pp. 2786-2799, 2023, doi: 10.1109/TIP.2023.3270770.
In the paper we present an efficient algorithm to approximate the Automatic Color Equalization (ACE) of an input color image, with an upper-bound on the introduced approximation error. The computation is based on Summed Area Tables and a carefully optimized partitioning of the plane into rectangular regions, resulting in a pseudo-linear asymptotic complexity with the n umber of pixels (against a quadratic straightforward computation of ACE). Our experimental evaluation confirms both the speedups and high accuracy, reaching lower approximation errors than existing approaches. We provide a publicly available reference implementation of our algorithm.

Publications

Books

J.J. McCann, V. Vonikakis, A. Rizzi, “HDR Scene Capture and Appearance”, SPIE Spotlight Series, Volume: SL35, Pages: 92, December 2017, ISBN: 9781510618541.

J.J. McCann, A. Rizzi, “The Art and Science of HDR Imaging”, John Wiley & Sons, Pages: XXV+389, November 2011, ISBN: 9780470666227.

Book Chapters

G. Simone, D. Gadia, I. Farup, A. Rizzi, “Ant Colony for Locality Foraging in Image Enhancement”, in Multi-Objective Swarm Intelligence: Theoretical Advances and Applications, Ed. Dehuri, Satchidananda, Jagadev, Alok Kumar Panda, Mrutyunjaya, Studies in Computational Intelligence, Vol. 592, Springer, 2015, ISNB: 978-3-662-46308-6, DOI: https://doi.org/10.1007/978-3-662-46309-3_5.

A. Rizzi, J. McCann, “Understanding glare and how it limits scene reproduction” in the Handbook of Digital Imaging, edited by M. Kriss. John Wiley & Sons, Ltd: Chichester, UK, pp. 433-458, February 2015, ISBN: 978-0-470-51059-9, DOI: https://doi.org/10.1002/9781118798706.hdi072.

M. Chambah, A. Rizzi, “Perception based digital motion picture restoration and quality evaluation”, in Colour-Coded, pp. 95-109, December 2010, ISBN 978-0-901956-86-6.

D. Marini, A. Rizzi, M. Rossi, “Color Appearance for Photorealistic Image Synthesis”, selected for Selected SPIE Papers on CD-ROM, Volume 24. Color Imaging: Device-Independent Color, Color Hard Copy, and Graphic Arts, October 2002, DOI: https://doi.org/10.1117/12.410791.

D. Marini, A. Rizzi, C. Carati, “Color Constancy Effects Measurement of the Retinex Theory”, selected for Selected SPIE Papers on CD-ROM, Volume 24. Color Imaging: Device-Independent Color, Color Hard Copy, and Graphic Arts, October 2002, DOI: https://doi.org/10.1117/12.334564.

Papers on international journals

Plutino A. and Tarini M., "Fast ACE (FACE): An Error-Bounded Approximation of Automatic Color Equalization," IEEE Transactions on Image Processing, vol. 32, pp. 2786-2799, 2023, DOI: 10.1109/TIP.2023.3270770

Plutino A., Barricelli B. R., Casiraghi E., Rizzi A., “Scoping review on automatic color equalization algorithm”, J. Electron. Imaging 30(2), 020901 (2021), DOI: 10.1117/1.JEI.30.2.020901

B.R. Barricelli, E. Casiraghi, J. Gliozzo, V. Huber, B. E. Leone, A. Rizzi, B. Vergani, “Ki67 nuclei detection and Ki67 index estimation: a novel automatic approach based on human vision modeling”, BMC Bioinformatics, Volume 20, Issue 1, pp. 1-14, December 2019, DOI: https://doi.org/10.1186/s12859-019-3285-4.

G. Gianini, C. Bonanomi, C. Mio, M. Anisetti, A. Rizzi, “Glare-removal as an ill-conditioned problem”, Journal of Electronic Imaging, Volume 28, Issue 6, 063014, December 2019, DOI: https://doi.org/10.1117/1.JEI.28.6.063014 .

A. Rizzi, B. Barricelli, C. Bonanomi, L. Albani, G. Gianini, “Visual Glare Limits in High Dynamic Range Displays for Medical Imaging”, IET Image Processing, Volume 12, Issue 7, pp.976 – 988, October 2018, DOI: https://doi.org/10.1049/iet-cvi.2018.5252.

F. Cozzi, C. Elia, G. Gerosa, F. Rocchetta, M.P. Lanaro, A. Rizzi, G. Gianini, “Use of an Occlusion Mask for Veiling Glare Removal in HDR Images”, Journal of Imaging, Volume 4, Issue 8, August 2018, DOI: https://doi.org/10.3390/jimaging4080100.

M. Lecca, A. Rizzi, G. Gianini, “Review and Comparison of Random Spray Retinex and of its variants STRESS and QBRIX”, Cultura e Scienza del Colore – Color Culture and Science, Volume 9, pp. 55-64, April 2018, DOI: https://doi.org/10.23738/ccsj.i92018.06.

M. Lecca, G. Simone, C. Bonanomi, A. Rizzi, “Point-based Spatial Color Sampling in Milano-Retinex: a Survey”, IET Image Processing, Volume 12, Issue 6, pp. 833-849, February 2018, DOI: https://doi.org/10.1049/iet-ipr.2017.1224.

C. Bonanomi, S. Balletti, M. Lecca, M. Anisetti, A. Rizzi, E. Damiani “I3D: a new dataset for testing denoising and demosaicing algorithms”, Multimedia Tools and Applications, Volume 79, Issue 13-14, pp. 8599 - 8626, July 2018, DOI: https://doi.org/10.1007/s11042-018-6396-4.

G. Gianini, A. Rizzi, “A Fuzzy Set Approach to Retinex Spray Sampling”, Multimedia Tools and Applications, Volume 76, Issue 23, pp. 24723-24748, June 2017, DOI: https://doi.org/10.1007/s11042-017-4877-5.

M. Lecca, C. M. Modena, A. Rizzi, “Using pixel intensity as a self- regulating threshold for deterministic image sampling in Milano Retinex: the T-Rex algorithm”, Journal of Electronic Imaging, Volume 27, Issue 1, pp. 011005-1 - 011005-11, January 2018, DOI: https://doi.org/10.1117/1.JEI.27.1.019801.

M. Lecca, A. Rizzi, R.P. Serapioni, “GRASS: A Gradient-based Random Sampling Scheme for Retinex ”, IEEE Transaction on Image Processing, Volume 26, Issue 6, pp. 2767-2780, June 2017, DOI: https://doi.org/10.1109/TIP.2017.2686652.

A. Rizzi, C. Bonanomi, “Milano Retinex family”, Journal of Electronic Imaging, Volume 26, Issue 3, pp. 031207-1 - 031207-7 , DOI: https://doi.org/10.1117/1.JEI.26.3.031207.

M. Lecca, A. Rizzi, R.P. Serapioni, “GREAT: A Gradient-based Color Sampling Scheme for Retinex”, Journal of the Optical Society of America A, Volume 34, Issue 4, pp. 513-522, April 2017, DOI: https://doi.org/10.1364/JOSAA.34.000513.

D. Marini, C. Bonanomi, A. Rizzi, “Perceptual contrast enhancement in visual rendering of astro-photographs”, Journal of Electronic Imaging, Volume 26, Issue 3, 031205, March 2017, DOI: https://doi.org/10.1117/1.JEI.26.3.031205.

G. Gianini, M. Lecca, A. Rizzi, “A population-based approach to point-sampling spatial color algorithms”, Journal of the Optical Society of America A, Volume 33, Issue 12, pp. 2396-2413, 2016, DOI: https://doi.org/10.1364/JOSAA.33.002396.

C. Fernandez-Maloigne, J. Moreno, A. Rizzi, C. Bonanomi, “QUALITAS: Image Quality Assessment for Stereoscopic Images.”, Journal of Imaging Science and Technology, Volume 60, Issue 5, pp. 50405-1-50405-13, September 2016, DOI: https://doi.org/10.2352/J.ImagingSci.Technol.2016.60.5.050405.

M. Lecca, A. Rizzi, G. Gianini, “Energy-driven path search for Termite Retinex”, Journal of Optical Society of America A, Volume 33, Issue 1, pp. 31-39, January 2016, DOI: https://doi.org/10.1364/JOSAA.33.000031.

G. Gianini, A. Manenti, A. Rizzi, “QBRIX: a Quantile-based Approach to Retinex”, Journal of the Optical Society of America A, Volume 31, Issue 12, pp. 2663-2673, 2014, DOI: https://doi.org/10.1364/JOSAA.31.002663.

G. Simone, G. Audino, I. Farup, F. Albregtsen, A. Rizzi, “Termite Retinex: A New Implementation based on a Colony of Intelligent Agents”, Journal of Electronic Imaging, Volume 23, Issue 1, 013006, January 2014, DOI: https://doi.org/10.1117/1.JEI.23.1.013006.

N. Richard, C. Fernandez-Maloigne, C. Bonanomi, A. Rizzi, “Fuzzy Color Image Segmentation using Watershed Transform”, Journal of Image and Graphics, Voulme 1, Issue 3, pp. 157-160, September 2013, DOI: http://dx.doi.org/10.12720/joig.1.3.157-160.

O. Kolarings, I. Farup, A. Rizzi, “Spatio-Temporal Retinex-Inspired Envelope with Stochastic Sampling: A Framework for Spatial Color Algorithms” Journal of Imaging Science and Technology, Volume 55, Issue 4, pp. 040503-1–040503-10, July 2011, DOI: https://doi.org/10.2352/J.ImagingSci.Technol.2011.55.4.040503, (IS&T Best Paper Award 2011).

S. Zuffi, C. Brambilla, R. Eschbach, A. Rizzi, “Comparing image preference in controlled and uncontrolled viewing conditions” Journal of Electronic Imaging, Volume 19 Issue 4, 043014, October 2010, DOI: https://doi.org/10.1117/1.3514732.

A. Rizzi, J.J. McCann, “Glare-limited Appearances in HDR Images”, Journal of the Society for Information Display, Volume 17, Issue 1, pp. 3-12, 2009, DOI: https://onlinelibrary.wiley.com/doi/abs/10.1889/JSID17.1.3.

E. Provenzi, C. Gatta, M. Fierro, A. Rizzi, “A Spatially Variant White Patch and Gray World Method for Color Image Enhancement Driven by Local Contrast”, IEEE Transactions on Pattern Analysis and Machine Intelligence, Volume 30, Issue 10, pp. 1757 - 1770, October 2008, DOI: https://doi.org/10.1109/TPAMI.2007.70827.

J.J. McCann, A. Rizzi, “Camera and visual veiling glare in HDR images” Journal of the Society for Information Display, Volume 15, Issue 9, pp. 721–730, 2007., DOI: https://doi.org/10.1889/1.2785205.

E. Provenzi, M. Fierro, A. Rizzi, L. De Carli, D. Gadia, D. Marini, “Random Spray Retinex: a new Retinex implementation to investigate the local properties of the model” IEEE Transactions on Image Processing, Volume 16, Issue 1, pp. 162-171, January 2007, DOI: https://doi.org/10.1109/TIP.2006.884946.

C. Gatta, A. Rizzi, D. Marini, “Local Linear LUT Method for Spatial Color Correction Algorithm Speed-up”, IEE Proceedings Vision, Image & Signal Processing, June 2006 - Volume 153, Issue 3, pp. 357-363, June 2006, DOI: https://doi.org/10.1049/ip-vis:20050279.

A. Artusi, C. Gatta, D. Marini, W. Purgathofer, A. Rizzi, “Speed-up Technique for a Local Automatic Color Equalization Model” Computer Graphics Forum, Volume 25, Issue 1, pp. 5–14 March 2006, DOI: https://doi.org/10.1111/j.1467-8659.2006.00914.x.

E. Provenzi, A. Rizzi, L. De Carli, D. Marini, “Mathematical definition and analysis of the Retinex algorithm” Journal of Optical Society of America A, Volume 22, Issue 12, pp. 2613-2621, December 2005, DOI: https://doi.org/10.1364/JOSAA.22.002613.

D. Marini, A. Rizzi, M. Rossi, “Postfiltering for Color Appearance in Synthetic Images Visualization”, Journal of Electronic Imaging, Volume 13, Issue 1, January 2004, DOI: https://doi.org/10.1117/1.1635367.

A. Rizzi, C. Gatta, D. Marini, “From Retinex to Automatic Color Equalization: issues in developing a new algorithm for unsupervised color equalization”, Journal of Electronic Imaging, Volume 13, Issue 1, pp. 75-84., January 2004, DOI: https://doi.org/10.1117/1.1635366.

A. Rizzi, D. Marini, L. Rovati, F. Docchio, “Unsupervised Corrections of Unknown Chromatic Dominants using a Brownian-Path-Based Retinex Algorithm”, Journal of Electronic Imaging, Volume 12, Issue 3, July 2003, DOI: https://doi.org/10.1117/1.1584051.

A. Rizzi, C. Gatta, D. Marini, “A New Algorithm for Unsupervised Global and Local Color Correction”, Pattern Recognition Letters, Volume 24, Issue 11, pp. 1663-1677, July 2003, DOI: https://doi.org/10.1016/S0167-8655(02)00323-9.

G. Ciocca, D. Marini, A. Rizzi, R. Schettini, S. Zuffi, “Retinex Preprocessing of Uncalibrated Images for Color Based Image Retrieval”, Journal of Electronic Imaging, Volume 12, Issue 1, pp. 161-172, January 2003, DOI: https://doi.org/10.1117/1.1526844.

Conference Proceedings

B. Sarti, A. Plutino, A. Rizzi, “Glare ottico nelle immagini iperspettrali”, XVI Conferenza del Colore, Colore e Colorimetria - Contributi Multidisciplinari - Vol. XVIA, pp. 26-33, Bergamo (Italy), 3-4 September 2020, https://www.gruppodelcolore.org/wp-content/uploads/2020/11/ColoreEcolorimetriaContributiMultidisciplinari_VolXVIA-1.pdf.

E. Casiraghi, B. Vergani, B. Barricelli, S. Liberini, B.E. Leone, A. Rizzi, “Ruolo del colore nello sviluppo di un sistema automatico per l’analisi di immagini istologiche di tessuto tumorale”, XV Conferenza del Colore, Colore e Colorimetria - Contributi Multidisciplinari - Vol. XVA, pp. 39-48, Macerata (Italy), 5-7 Settembre 2019, https://www.gruppodelcolore.org/wp-content/uploads/2019/11/Colore-e-Colorimetria.ContributiMultidisciplinari_Vol-XVA.pdf.

A. Plutino, M. Lecca, A. Rizzi, “A Cockpit of Measures for Image Quality Assessment in Digital Film Restoration”, International Conference on Image Analysis and Processing (ICIAP), New Trends in Image Analysis and Processing, pp. 159-169, September 2019, DOI: https://doi.org/10.1007/978-3-030-30754-7_16.

S. Liberini, M.P. Lanaro, M. Rossi, A. Rizzi, “About glare and luminance measurements”, Electronic Imaging, Color Imaging XXIV: Displaying, Processing, Hardcopy, and Applications, pp. 84-1-84-6, San Francisco (USA), 13-17 January 2019, DOI: https://doi.org/10.2352/ISSN.2470-1173.2019.14.COLOR-084.

M. Lecca, G. Simone, A. Rizzi, “Milano Retinex Paths as Local Minima of an Energy Functional with Tunable Color and Spatial information”, SIAM Conference on Imaging Science, Bologna (Italy), 5-8 June 2018.

M. Lecca, C.M. Modena, A. Rizzi, “T-Rex: A Milano Retinex Implementation based on Intensity Thresholding”, 6th Computational Color Imaging Workshop (CCIW'17), LCNS 10213 Lecture Notes in Computer Science, Milan (Italy), 29-31 March 2017, DOI: https://doi.org/10.1007/978-3-319-56010-6.