@Martin_Weiss In your “one more thing” you appear to reference statements by @friolator, so I would let him respond to those.
In regards to my prior statement, you appear to be quite defensive about my reference to the grant the start up may have benefit from. If the Swiss National Science Foundation Bridge Discovery Grant, and the Universität Zürich allow it, there is nothing wrong with it.
The lengthy explanations do not change the past.
In particular in regards to:
In an effort to clarify my prior statement that you have so extensively challenged:
I am happy to accept, and make it very clear:
For transparency, you are a founding member of a new company, scan2screen, a startup which bears the same name( and logo) used for a grant funded project, and that the intellectual property basis of the startup is the prior research of its funders, as clearly enumerated in the startup company website. The prior research was done prior to the founding of the company, while the participants (some founders) worked for other institutions such as the University of Zurich.
@Martin_Weiss The part which I respectfully disagree with is:
In my opinion -and everyone is entitled to their own- If the prior research and intellectual property was not paid for the startup one would have to be very naive to believe your statements on funding.
Given that the subject matter of this forum, and of this thread is not startup intellectual property benefits, I will focus on the subject The Backlight.
Look forward to seeing your knowledge contributions in this and other subjects, specially if those include specifics.
Cameras do not have broadband filters for quantity of light. The broad filters are such to -as best as these can- represent each color (RGB) spectral band as perceived by the human receptors and capture this representation as a numeric combination of the primary colors.
Would you like to see a great illustration of filtering with light? check out the use of narrow band illuminant (low pressure sodium vapor light) .
Since you have the perspective of a cameraman, and in the interest of sharing knowledge and dispel arguments, I would refer you to the very well documented study of narrow band illumination by the Academy of Motion Pictures Arts and Science. In the videos, the presentations by Jonathan Erland illustrates well the perils of recording reflected light from narrow-band light, similar perils applicable to capturing direct light filtered by the film. His presentation is substantiated with specifics, and to quote from his technical Oscar acceptance speech
Concerned to such issues basic to the cinema process such as light and time. Light in the form of the quality of light produced by the newest instruments including solid state LEDs and time in the form of frame-rates and various techniques by which the cinematographer becomes the master of time itself.
His presentation of chromatic chaos is a master class of the effect of different light spectrum. A portion of the presentation makes an analogy to paint, and a blank canvas, and he says:
Within that metaphor then, the combination of a 3200K balanced stock and a 3200K light source or a very close simulation thereof, the default condition.
Represents the white blank gesso canvas that an artist confronts as he begins a painting. In the course of executing the painting he may impose all manner of changes and effects upon that canvas that after all is the essence of art, but he is entitled to expect the blank pure white canvas as his starting place.
A light source differing from the standards studio tungsten source, specially a discontinuous one, will preemptively impose a color cast on the canvas that will be difficult or impossible to subsequently correct.
While the above is in the framework of reflected light to film exposure, the effects of discontinuous direct light for scanning with a camera sensor -the white gesso canvas of film scanning- would also impose a cast in colors.
@npiegdon that approach basically attempts the very close simulation thereof referenced above.
By providing multiple-discrete narrow bands, a discrete spectrum source is simulating a wider spectrum, while maintaining the advantages of narrow-band illumination for color separation.
One should also consider there are multiple ways of fading. The film die can fade in intensity only, preserving its passing band, and/or may fade in die-color, where the die color is no longer the same as the original.
As the International Commission on Illumination (CIE) - Color Science Basics For Filmmakers previously posted indicates:
- All visible colors can be described with X Y and Z values.
- Colors with equal XYZ values will appear identical, even with different scpectral power distributions.
- No three primaries exists which would reproduce all colors.
The solution is an XYZ image sensor (looking for one for the RPi4 or 5 
). Unfortunately, while there are XYZ light sensors, I haven’t found an image XYZ one.
One of those XYZ image sensors, and a white light source, and it is the end of the discussion. Every pixel will have its current visible color. End of discussion.
In the meantime, one would have to wear the light and sensor that is best for their requirement (and budget).
After almost two years, I will update/clarify my hypothesis above.
Bn should be captured with multiple narrow band LEDs within the blue channel of the sensor.
Rn should be captured with multiple narrow band LEDs within the red channel of the sensor.
The above may be achieved with a full spectrum image sensor, 3 exposures.
For those on a budget -like me- two raw exposures of an RGB sensor should be as close as the budget permits.
Exposure 1 - White light, resulting in Yw (arithmetically calculated), Rw, Bw, and Gw.
Exposure 2 - Red LEDs and Blue LEDs, resulting in Rn, and Bn.
I would add that the light of Exposure 2 should be set to obtain the best quantization for R and B channels, rather than to seek balance. That is especially useful to achieve adequate S/N for these colors in faded film.
The hypothesis is in line with the mission statements borrowed from @friolator and @cpixip.
@npiegdon @cpixip thank you for sharing valuable knowledge on the subject, this is a great topic and there is much to learn.
Updated:
- Incorporated suggestion by @npiegdon.
- Added XYZ light sensor link to Texas Instruments reference: Choosing Between RGB and XYZ Color Sensors.