Your Ortho and Panchromatic examples look very convincing. I would like to understand how the spectral sensitivity curve of a film or film with a filter is applied to the input RGB image. I tried to figure out how to convert from (r, g, b) to wavelength but could not find a satisfactory solution.
Ah, this a good question, how to go from RGB to spectral, much debated. There are naive solutions (that almost work) and complicated solutions (too much computing power is needed). Always go the "way of the middle"...
For the rest: even for B&W results, I take the RGB color values of each original image pixel (linear values, in fact an intensity). I compute from this their wavelength levels, discretized with a 10nm interval between 380 and 730 nm, which gives a new spectral chart for
this color (using some specially crafted data derived from daylight spectrum). Using the same system for all my curves, I can add, subtract, multiply and divide, combine them to obtain different effects (additive and subtractive color mixing for example).
For color filters, it is just a multiplication, after preparing a special spectral chart from the original. All is a queston of discretized intensity levels.
Finally I use the discretized values of the "final" spectrum to compute a global "level of energy", that is used with the HD curve as the "exposure", and that gives me a density for each original pixel.
Color films work the same way, they are just B&W layers on top of each other, responding to a certain part of the spectrum. Modern negative films have a fourth orange layer that must be considered in the process.
This is why my examples look so good, it's because all the computing done was made from real physical principles! Well, a bit tuned, but the
basic principles are respected.
I could check what I produced with digital vs film photos examples found on the web, using the same point of vue, so comparison is easy. I took the digital version, applied the same "film" and compared my result with the "real" film version. That's how I could improve and tune the way of computing the whole process, trying to stick more and more closely to "real life" examples.
This is the first time I'm showing this to people who have much more analog photography experience than me... and my work seems to be appreciated. If other people want to comment no problem
