[biz-engineer]

In essence, you take the digital image, undo what the sensor did to the light, colors, and patterns to get an estimate of the true scene, and then you apply the film's transformation of light, colors, and patterns to get the film result. Of course, with a bit of math, you can go directly from digital to film without computing a file with the intermediate scene, but conceptually it is a digital->-scene->film process.

I assume the raw file data response to light would be linear. The conversion would work within the CFA color space of the digital sensor.

Some guys have already worked on that: https://www.photo.net/discuss/threads/whats-the-real-colour-space-of-film.464422/ . As you mentioned earlier, it may not be possible to replicate the film look in digital; both Ektachrome and Velvia are able to record reds that are even outside the Adobe RGB color space.

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Last edited by biz-engineer; 02-23-2019 at 11:28 AM.

[stevebrot]

I have been uniformly disappointed with the various plug-ins and presets claiming to provide emulation of particular emulsions. At issue is the fact that the behavior of say, Kodachrome 64, varies with subject and light. Below is a scan from one of the last rolls of K64 made. An attempted K64 emulation of a digital capture of the same subject will likely show more contrast and saturation than what the film actually recorded, the original showing off a few of K64's hidden character aspects.



As a result, I don't attempt attempt film emulation on color images except in a fit of whimsy. Below is a reasonable approximation of Ferrania Solaris 100 (minus grain). Those familiar with the film may judge whether I was successful.



That being said, monochrome conversions are another matter entirely. While I don't attempt to emulate a particular film, I do use a set of Lightroom presets that allow a very decent approximation of particular film types (orthopanchromatic vs. super-panchromatic vs. IR, for example) as well as applying color correction filters as one might in the field and various darkroom tweaks as well. While there is zero attempt at grain emulation, the actual results are reasonably similar to what I might expect from several of the films I use and how I use them. The example below is very similar to what I would expect from Rollei Retro 100 or TMax 100 with yellow filter and selenium toning.



The unfortunate thing is that the (free) preset package I use (called Monochrome Toolkit) is not longer featured on the creator's Web site and is hard to find as a result. I will post the link if I can find it.


Steve

[photoptimist]

I assume the raw file data response to light would be linear. The conversion would work within the CFA color space of the digital sensor.

Yes, the raw file would be linear with an offset for any uncorrected dark current. There would be an MTF associated with the raw Bayer pattern but probably a different MTF curve for any non-trivial demosaicer.

Most of the work would be in the color space issues.

Some guys have already worked on that: What's the REAL colour space of film? | Photo.net Photography Forums . As you mentioned earlier, it may not be possible to replicate the film look in digital; both Ektachrome and Velvia are able to record reds that are even outside the Adobe RGB color space.

Indeed! And presumably this also impacts scans of these films.

[biz-engineer]

The unfortunate thing is that the (free) preset package I use (called Monochrome Toolkit) is not longer featured on the creator's Web site and is hard to find as a result. I will post the link if I can find it.

Thanks for the post with example photographs. This is a domain where I know nearly nothing (beside having used to simple press-button functions), but definitely worth studying the subject, it's like a new road opening up in front of me.

[biz-engineer]

Digital tone curves are perfect, primarily aiming at loyal color reproduction once general white balance is set. Opening up presets, I've figured that the film look emulation is achieved by displacing the RGB tone curves (3D LUT?) so that to emulate the not so loyal color reproduction of a type film. The interplay of curve in 3 dimensions isn't obvious, but understanding the effect is good for exploring the practice of what's called "color grading".