Monday, November 14, 2016

Paradox Lost

In the Spring 2016 issue (#474) of ISCC News, I described what appeared to be a paradox that emerged from an exercise for students [1]: “If the wavelength of the green line of mercury is 546 nm in a vacuum, what is it in water? In heavy flint glass? [410 nm, 331 nm].” Would change of refractory material abutting the eye’s photoreceptors cause the color of a light to change as drastically as suggested here? More precisely, would changing the refractive index change the tristimulus values of a light with emitted spectral power distribution E(λ)?

Unlike in the wavelength domain, the change of refraction index would not affect the frequency of the transmitted light. I concluded that the proper choice of integration domain in which to perform tristimulus integration should be a matter of experiment.  This conclusion was incorrect. As often happens when one poses a paradox, closer examination provides a resolution. The tristimulus values should not change if the integrals are performed properly.  I describe the resolution in a tutorial note recently posted for publication in Color Research and Application [2].

It is reasonable and respectful of physical principles that a tristimulus value [say, M = the integral over λ of  E(λ) m(λ)] should not depend on the domain of integration used to obtain it. In [2] it is shown that the domain invariance from wavelength λ to frequency ν = c/λ is assured if the spectral power distribution of the test light in frequency is represented as E*(ν) =|dλ/dν| E(λ(ν)).

 Now imagine a transformation from frequency to two alternative wavelength domains λ1 = c1/ν  and λ2 = c2/ν , where c1 and c2 represent speeds of light in different refractive indices (possibly functions of ν ).  Here, M doesn’t change either; rather, the spectral power distribution E*(ν) is multiplied by the Jacobian |dλ1/dν  |-1 or | dλ2/dν |-1, respectively. (Things get a bit more complicated when λ1 or λ2 is a nonmonotonic function of ν , but the principle is the same.) Of course, changing from λ1 to λ2 is equivalent to changing from λ1 to ν  and then from ν  to λ2.  There is no predicted variation of M, by construction.

So my “gentle paradox” evaporates by construction. Obeying the rules of mathematics leads back to where one started: tristimulus values don’t depend on the refractive index of the transmitted medium.
 
Where does that leave the role of experiment? If one were to measure the camera version of tristimulus values in different refractive media (say, with M being a measured camera value for a light E through a camera sensitivity function m), we would expect no change in those values.  But experiment can trump theory. If M were observed to change, then a new paradox would surface. From “paradox lost” we would see “paradox regained.”

References:
[1]. HQ Fuller, RM. Fuller, and RG Fuller, Physics Including Human Applications. Harper and Row, 1978. Revised electronic version copyright 2009 by RG Fuller. http://physics.doane.edu/hpp/Resources/Fuller3/pdf/F3Chapter_19.pdf exercise 2, p. 436.
[2] MH Brill, Ways to define a tristimulus value. Color Res. Appl. 2016, Early View, DOI 10.1002/col.22079.

Michael H. Brill
Datacolor

Thursday, August 4, 2016

From Color Science to Privacy

[Here is the latest word from Michael Stokes, architect of sRGB, a founder of ICC, Interest Group II chair of ISCC, …, and ten years absent from the field of color.]




I grew up in my family’s slide duplication and photofinishing business back when E4 processing was still new, and Kodachrome, FujiChrome and AgfaChrome were widely available. The business grew to the point my parents bought entire emulsion runs of motion picture and inter-negative stock from Kodak to ensure consistent quality. Our computer system tracked every action taken of each slide or component of each order, and we offered an unconditional money-back guarantee. I was responsible for the quality and production aspects of the business, so I spent what seemed like endless time trying to understand why it was so difficult to craft color reproduction processes that were consistent and accurate. 

In the late 1980s, I joined RIT’s Color Science Master’s program and soon my frustration transformed in wonder and awe that we were able to reproduce color reasonably well given the many complex aspects involved. I was fortunate enough to have a successful color career at Apple, then at Hewlett-Packard, and finally at Microsoft as their Color Architect. Over this period, I helped to lead industry efforts such as the founding of the ICC, standardization of sRGB and scRGB, evolution of ColorSync and ICM, as well as taking part in the founding of CIE’s Imaging Science Division. I often explained the goal of my efforts as trying to reverse engineer a large part of the human brain to effectively model it across a complex system of components from many stakeholders who didn’t always get along with each other. 

I joined Microsoft in 1999 in hopes of implementing the best-in-class color reproduction software development systems. By 2006 we had successfully implemented advanced hybrid solutions that supported sRGB, scRGB, and ICCv4 as well as CIECAM color vision modeling. This was a part of Windows Vista, which was known to have significant challenges. 

It soon became clear that advanced color systems were not the most pressing need for the company, and I transferred to Microsoft’s newly established Health Solutions Group (HSG). As part of this transition, the company required that I no longer participate in the color field and have no communications regarding color with my many friends and colleagues that I had established over many years. It was a difficult personal decision, but in the end, I chose to put my family’s financial stability first. I am sincerely and deeply sorry for the negative impact this has had on my communications and relationships with many dear color friends and colleagues.

My original job description focused on health standards and patents, in which I had significant experience from my color science background having worked with IEC, CIE and ISO as well as accumulating over 50 patents. Within two weeks, my role grew to include a focus on security and privacy. I had security experience having designed and written color and imaging components in the Windows kernel software. Privacy was completely new. 

It turns out that privacy is very much like color reproduction. The goal is to understand human desires and perceptions around information data flows, controls, and ownership to effectively model these desires and perceptions across a complex system of components from many stakeholders who don’t always get along with each other, including regulators, legislators, and consumer advocates. 

I was again extremely fortunate to enjoy a second successful career, including testifying before the US Senate Judiciary Committee, visiting numerous national and international regulators including the US Food and Drug Administration, US Federal Trade Commission, and CNIL  (French Data Protection Authority).
 
When Microsoft divested HSG into an independent subsidiary jointly owned by General Electric (and now wholly owned by General Electric), I again chose to put my family’s financial stability first and stay at Microsoft. I now help manage privacy for many of Microsoft Office client applications including Word, Excel, PowerPoint and OneNote among others. I believe I have one of the best jobs in the company, helping design architectures and processes to empower our users to best achieve their desires. 

The major regret I have had in my career was not being able to explain why I “went dark” from all of my color friends. I hope this article sheds some light on those difficult days and deeply appreciate the opportunity that ISCC has provided me. I know I owe two successful careers to my friends and colleagues in color science who taught me so much about color, and even more about life.

Thank you,
Michael Stokes, mistokes-color@outlook.com