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2 months in the USA for Emilie
Emilie Robert, doctoral student at DEOS/CIMI (ED-AA) and whose thesis is on the science of colors, went on a research exchange to the USA at the Munsell Color Science Laboratory (MCSL) in Rochester. During 2 months, she was able to propose a new experience to the MCSL team allowing her to complete one of the two studies of her thesis whose subject is: Study and modeling of a vision system with high color fidelity.
CAN YOU EXPLAIN TO US WHAT YOUR THESIS WORK CONSISTS OF?
The images of our daily life of the 21st century are acquired and viewed in color. Our televisions, our telephones and computers, all allow an indirect vision – scene -> acquisition system -> display system -> eye – with the illusion of an optimal concordance with the direct vision – scene -> eye, that we carry to the world which surrounds us.
For certain imaging applications that are extremely demanding in terms of colorimetry, such as the film industry, the textile industry, surveillance, or even space exploration, this illusion is regularly altered by the extreme acquisition conditions encountered.
My thesis work aims at defining methods for the reproduction of digital images of very high color quality. Thus my work revolves around two axes: the spectral sensitivity of the human eye, and the chain of processing of color information by modern image sensors. Two studies are conducted on (i) the method for calculating the color correction matrix, and (ii) taking into account individual variations in human color vision. The studies carried out during my thesis aim at defining which of these two aspects of the chain of the indirect vision, largely studied independently of each other, is at the origin of the most important disorders for the colorimetric fidelity.
DEOS-CIMI, my host laboratory at ISAE SUPAERO wished to complete its expertise in image sensors for space and defense applications through this thesis and in collaboration with the Institut de Recherche Biomédicale des Armées (IRBA) and the DGA Techniques Aéronautiques (DGA-TA). Thus the interest of this work and the resulting manuscript is first to allow the appropriation of the foundations of color science and digital image processing by the CIMI team in order to constitute this new expertise of color imaging in the laboratory.
WHY YOU LEFT
IN THE UNITED STATES, ROCHESTER ?
After an important work of literature study at the beginning of the thesis, the spectral characterization of the image sensors developed at CIMI, and the development in progress of a measurement bench of the spectral characteristics of the human eye, it turned out at mid-thesis that exchanging with knowledgeable researchers in the field of color science would be of a major interest So, guided by my scientific readings I had my 1st exchange with Mark Fairchild, professor and director of the Color Science program at RIT’s Munsell Color Science Laboratory (MCSL), in April 2020 in full lockdown. He quickly proposed me to spend a few months, as soon as the health conditions would allow it, with the other PhD students of his study program in the MCSL laboratory. Our idea was first to compare two methods of measuring the spectral characteristics of the human eye, ours developed at ISAE SUPAERO, and theirs developed during two PhD theses between 2008 and 2016. However, the health crisis and other hazards on both sides did not allow us to make this initially planned comparison. So as soon as I arrived in Rochester at the end of August 2021, after I was able to present my work to the team in more detail, I had the opportunity to propose a new experiment to be conducted during my time with them. It allowed to complete one of the two main studies of my thesis which aims at quantifying the residual errors after applying a color correction on an image. The study focuses on two types of scenes: those with restricted spectral characteristics, and those that do not allow the use of calibration charts.
WHAT WAS YOUR EXPERIENCE AT RIT (ROCHESTER INSTITUTE OF TECHNOLOGY)?
My experience at RIT has focused on optimizing the correction to be applied for particular images that have restrictions on the color domain present in the scene (Figure 1). For this purpose I had the opportunity to use the “Next Generation Target” calibration sight (Figure 2 and Figure 3) recently developed by Avian Rochester, LLC a company founded by Prof. Dr. G. K. K. K. K. David Wyble of MCSL. It contains 130 color patches rather than the 24 patches offered by the Classic® X-rite test pattern widely used in all fields to define the correction to be applied to a digital image in order to allow a color rendering more faithful to human vision. This large number of patches allowed us to compute corrections for patches corresponding only to a type of hue of interest (example shown in figure 1: correction computed on red-orange patches for the Mars image, correction computed on green patches for the forest image, …) and thus to do hue-specific image processing for imaging applications extremely demanding in terms of colorimetry.
You spent 2 months there, how did you feel?
I am delighted with this stay, which has given me a lot of confidence in the skills I have acquired throughout my thesis. I also learned a lot about the language commonly used in my field of research. Learning a new field always starts with learning the vocabulary related to it and since scientific literature is mainly published in English, bringing an expertise to France means using a vocabulary that is sometimes transformed by translation. With this exchange at the end of my thesis, I was able to readjust my “study language”.
This mobility took place at the very end of the thesis, mainly for reasons related to COVID-19. In fact, I started writing my manuscript at the same time as I was adapting to my new environment (laboratory, daily contacts, food, lifestyle). I must admit that it was a challenge but it was a very rich learning experience. Each discussion I had at MCSL made my understanding of each of my past and current study findings more complete. Since I was in the middle of writing, after each day in the lab, I had the opportunity to build on all the knowledge I had gained during the day by adding new ideas, discussions, and perspectives to my manuscript.
My stay at RIT, initially with the aim of working alongside experts in color science, also turned out to be an opportunity to discuss the post-doctoral project for which we had the joy of obtaining funding from the CNES. During 1 or 2 years, in collaboration with CNES/ISAE/MCSL, we will study recent and numerous images of Mars in order to understand which steps of the current image processing could deteriorate their colorimetric rendering. This deterioration will be measured and new correction methods will be proposed to allow a rendering of Martian images as they would appear to us if we were actually on the red planet. During my stay at MSCL I was able to set up the first collaborative meeting for the implementation of this project.
Despite a rather well thought out budget, I was surprised to discover a New York State law that applies to all universities and requires the subscription to a “Meal Plan” for each student who stays in an official university residence. This is the only housing solution offered to visiting students by RIT’s international department and is indeed a practical solution since renting an apartment for 2 months is rather complicated and expensive in the USA. Only staying in such a residence increases the food budget considerably. From an initial forecast of 800€ for the whole mobility (based on my food budget in France), the budget doubled because of the subscription to the “Meal Plan” whose amount is fixed (1539€). Money paid into the Meal Plan for on-campus food is non-refundable and only transferable to the next semester’s Meal Plan. This solution, probably well adapted to local students, turned out to be rather disturbing in my case as a mobile doctoral student. At the end of my stay, $800 remained on my Meal Plan. After many discussions with many people to try to get this money back, when I realized that it was impossible I made the decision to spend the rest at the campus supermarket and donate all the purchases to RIT’s “FoodShare” which distributes non-perishable food to students in need.
WERE YOU ABLE TO ENJOY THE UNITED STATES OUTSIDE OF YOUR TIME AT RIT?
I end this review of my thesis mobility with some pictures of my extra-academic activities around Rochester, NY, USA. This was my very first trip to the USA and I had the wonderful opportunity to visit the cities of New York and Washington DC, Niagara Falls, as well as the small town of Corning and its glass museum.
Rochester was the center of the 19th century imaging industry when George Eastman founded his now widely known KODAK company. His incredible work in photography is now remembered in a museum attached to his former home in East Rochester. A must-see for any PhD student or student in the field of image sensors.
In Washington DC, I had the incredible chance to visit the Air and Space Museum and to enjoy the observation of major pieces of the space conquest such as: the shuttle Discovery (the real one!!). I also got to see the DeLorean (the real one too!!) from back from the future it seems.
THE testimony of Emilie Robert
Now a doctor
I returned from my stay in November 2021, since then I am looking forward to the collaboration developed with the MCSL team and the work we still have to conduct during my post-doc at CNES.
I thank the foundation and its donors, without their help and that of the doctoral training of ISAE-SUPAERO, this stay which brought me a lot on all levels, would not have been possible!