Digitizing film using DSLR and RGB LED lights

[ggbutcher (Glenn Butcher)]

@Entropy512

Because I’ve almost completely eliminated any effect the camera’s CFA has on color management, I can now generate a DCP profile based on the film datasheet SSFs, and use THAT as the camera profile in RawTherapee. The process for doing so is EXACTLY the same as doing so for a digital sensor - I used dcamprof’s documentation with no special steps at all. So all of the tips @ggbutcher gave you are actually valid for this workflow!

Oh, someone tell my wife, I inadvertently got something right…

[Entropy512 (Andy Dodd)]

@dafranc

If possible, I’d really appreciate any guidance you could share on how to gather the SSF data from film datasheets using the plotting tool. I’d love to build an input profile for Portra 400, which is the film I use the most, but I honestly don’t know how to use the plotting tools to derive those curves into the kind of data that ends up in your CSV files.

Take a look at the documentation for WebPlotDigitizer - https://automeris.io/ - I cannot remember if I used the online version or the old opensource version selfhosted at this point.

There is a possibility the output format from WebPlotDigitizer might have changed since I last updated the repo. If you provide an example of recent output from tracing a datasheet, I can take a look.

You will manually have to make a small adjustment to the CSVs - the column headers output by WebPlotDigitizer look something like
Red,,Green,,Blue,
They need to look like:
Red,Red,Green,Green,Blue,Blue

Do you have a link to a Portra 400 datasheet?

If you’re working with already-color-converted inputs, you’re going to have a whole pile of additional layers of math to deal with that are just a big ??? for me. You might want to look at the Spektrafilm project that has been discussed here for ideas of the transformations needed here… It might help you, it might not, I’m not sure.

At some point I need to improve the documentation in that repository… First I need to finish scanning all of my negatives! I think I got around 3/4 of the way through and then became busy with other things.

[dafranc (Daniel)]

Okay! I’m going to take a look at the documentation you sent me and see what I can manage to do with WebPlotDigitizer.

In regards to color-converted inputs… I’ve basically been following two different approaches.

The first one is handling the DNG files through RawTherapee, doing what I consider a somewhat adequate color management there in regards to the input profile. For quite a while now, I’ve been experimenting with different input profile approaches that, within my limited understanding, seem to provide a better handling of the negative’s color space.

After processing the scans as linear negative gamma, I export them as negative linear TIFFs or EXRs, usually in ACES AP1 or Rec.2020, and then import them into DaVinci Resolve. From there, I work using several DCTLs that allow me to perform the inversion following a Cineon-style process.

I’ve also worked by importing the DNGs directly into Resolve. The decoding options there feel a bit vague and uncertain, but somehow I’ve still managed to get some pleasing results that way.

With the Resolve 21 update and the new photo module, things actually look pretty promising, and it seems like the results could improve further.

However, out of everything I’ve seen recently, your approach of creating an input profile using SSF feels like the one that makes the most sense to me, and it’s something I genuinely want to pursue.

I will upload a Portra datasheet I found.
e4050_portra_400.pdf (256.0 KB)