The appimage for the development version of RawTherapee is here. Release Automated Builds · Beep6581/RawTherapee · GitHub
When processing negatives, the White Balance tool should always be set to the values of the backlight. Simply make a shot without a negative, set the Neutral profile, use the color picker, readout the Temperature and Tint and apply that to your negative image
I don’t understand why you would want to do this. I would think you would be better off to set it through unexposed developed film if you are lucky enough to have an unexposed frame of film.
I also don’t understand how this would work since if I do the sequence set profile to neutral, turn off white balance, film negative, pick neutral spots, turn on white balance and use the pick option to select the unexposed border of the picture (which usually gives me a reasonable starting point) then copy that processing to the rest of the frames of the roll of film, I end up having to do the white balance pick of the unexposed boarder to every single frame to correct the color. So the white balance is not stable frame to frame.
As to point 5, I am using the RGB light source to normalize the ADC values of the R, G, and B sensors in the camera through unexposed film to near full scale in an attempt to maximize the color resolution captured.
My goal is not just to get nice jpeg copies of the film images, but to capture as much information as possible from the original negative in the raw file for archiving.
I am uploading another picture that includes people. Since it is a more normal picture with people in it, I did not have as much trouble with the software fighting me. So far I have only converted this to a positive and done the white balance. I have not adjusted exposure, black level lightness, saturation or contrast. I’m not sure what good this one will do because it is not causing me problems.
DSC04530.ARW (82.1 MB)
DSC04530.ARW.pp3 (11.2 KB)
Which of the two appimages should I be using?
Here’s a short tutorial on the using the development version of RT for colour negatives. I would certainly welcome corrections or suggestions from @rom9 and @paperdigits.
Before shooting the negatives, set the camera white balance to the light source, in my case this is an LED light panel.
Important note: Do not use the white balance eyedropper tool in the top left of the screen. It’s not meant for negatives and will revert the image to a negative. Instead, you can use “Pick white balance spot” in the “Film Negative” tool under the color tab in the right panel.
This image was processed without using the adjustments available in the “Film Negative” tool, although there are times when the sliders and “Pick white balance spot” are useful. I rarely use the “Pick neutral spots” because it’s hard to find two neutral spots (one lighter than the other) on these historical negatives. If you’re shooting film, however, you could shoot a gray scale or Macbeth chart with each roll to get these neutral spots.
Slide 1.
At the top right of the screen the White Balance is set to “Camera”, which shows the color temperature and tint of the light panel. Don’t adjust this.
Above that, where the screen shot says “Neutral”, press that and navigate to “Bundled profiles”, then “Film Negative”.
Slide 2.
“Film Negative” is selected. The image is now a positive, but needs to be cropped and is too dark.
Slide 3.
Adjust the “Exposure compensation” slider so that the histogram in the top left of the screen is approximately centered.
In “Film curve 1”, try “Auto-Matched Tone Curve” first. This can also be set manually if it works better for a particular image.
In “Film curve 2”, move the bottom left and top right of the curve so that the histogram in the top left of the screen goes to the left and right edges, without clipping.
If needed at this point you can make further adjustments to “Lightness, contrast, saturation” and “Shadows/highlights” if desired.
Slide 4.
The photo was taken late in the day with warm light. I wanted to preserve that, but I used “Color Toning” to cool it slightly.
Final version. I brightened it a bit more in curves and increased blue in the highlights, then in Gimp cleaned up a few specs of dirt and added a bit of sharpening.
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Use the latest appimage with “dev” in the name. At this time it’s from 20210614.
@DAP @troodon Please consider whether your comments about using Film Negative would be better suited in the appropriate thread: Any interest in a "film negative" feature in RT ?
@rom9 Can probably explain better, but this is the recommended procedure. I believe this is because your negatives on film have been shot with a different illuminant than you use when digitizing them. You want to compensate for the latter by taking a shot of your illuminant only and setting that as the white balance of your image and then use the Film Negative tool to pick/set the white balance of your negative.
I understand now. Can you share a file where you only shot through unexposed film?
I assume the second image you shared contains a completely uncovered area on the right? These are completely clipped to the limit of your sensor and therefore cannot be used for white balancing (neither in the White Balance tool or the Film Negative tool). As per the described procedure where you need to know the white balance of your light source, this makes it much harder to get good results easily.
Edit: I forgot to mention, but your images so far look extremely pink. This makes me wonder what is going on, because other negatives shared on this forum that I’ve seen were never that off-colour.
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That particular roll did not have any unexposed frames. On most rolls, there is often a bit of unexposed film before the first frame, or after the last frame. I use those to adjust the color of the light source, but I do not keep those images once I have the color correct for that film. This needs to be done for every film type and for Kodak, for every roll. (Kodaks quality control was terrible.) All images have unexposed areas on at least three sides of the image, the fourth side is sometimes cut off exposing the light source (the developers cut the strips into four frame segments, and did not always do a good job of getting the cut between frames). I usually try to use that unexposed area to set my black point, but some frames are badly under exposed, and to get anything useful at all the black point needs to be significantly lower.
Those images were captured before I got any advice from this forum. I have not done anything with the cameras white balance, I had not been using that. I figured the cameras white balance would be useless since negatives have such a huge color bias built into them to deal with color films color sensitivity.
The camera settings don’t matter, because they don’t affect the raw files. But since you have been tinkering with your light source, I wondered what the effect of that is.
Ah too bad, that might have helped finding a better workflow for you. Do you maybe have an image just exposing your light source, but not overexposed in the camera? Doesn’t matter if it’s a few stops down.
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I might be able to get an image of the light source tomorrow night. In the mean time, I’ll include the settings I’m using for various film types I have run into, as well as a light source characterization I did.
Sheet one of the light source characterization was proving to myself that the brightness adjustment was linear for each LED color. Sheet two was measuring the linearity of the camera sensor. The spectrum of the color LEDs is not extremely narrow, so the blue LED is picked up by the green sensor, and the green LED is picked up by the blue sensor. I figure this will not be a problem since i’m just trying to bias the spectrum to counter the color of the film and the sensitivity bias in the camera.
LightSourceCharactarization.ods (37.8 KB)
Light Source Settings.ods (20.0 KB)
these are both libre office spreadsheets. Excel will probably open them without problems but will spew FUD about them being dangerous (they are not).
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Hi all! Sorry for the late reply, i was offline…
The correct procedure to use the latest version was already explained in the posts above 
The initial problem was due to the older version: in the 5.8 release, the Film Negative tool was indeed working before demosaic, and did some estimation of median channel values to “guess” a reasonable output white balance.
The ability to copy-paste the same parameters and get consistent results when scanning an entire roll, was one of the main reasons for the update, which is now in the development version of RT 
With the new version, as long you keep the same backlight and camera settings while shooting the entire roll, you can adjust one frame, then copy-paste the processing profile on all the others.
Yes, you will notice over- and under-exposed frames, since nothing is auto adjusted
Regarding the backlight… from a signal processing point of view, trying to maximize the range on each channel makes a lot of sense. The problem is, that this “artificial” light should be taken into account in the camera input profile, which is not trivial.
The easy and intuitive solution that we’ve found to work reasonably well in most cases, is to use a white backlight, possibly close to daylight, and then apply the normal input profile also used for regular digital pictures. This gives an accurate representation of the negative to start with.
Now that said, the filmneg tool also gives you some flexibility for experimentation.
With the Inversion color space combo box, you can choose whether to perform the inversion before or after input profile conversion.
You could also create a custom ICC input profile for your adjusted RGB light, and try using that in place of the standard input profile. Unfortunately, i don’t have a ready-to-use “recipe” for this use case, you’ll have to do some experiments.
Oh, one final note: using Camera WB is ok as long as the camera itself is not set to AWB, otherwise you’ll get different multipliers on each shot (ok, sorry if it sounds obivous, just wanted to make it clear )
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I just converted two rolls that I digitized yesterday, and can say that the dev version is a HUGE improvement. I used the film negative profile, and adjusted the black level so the spike in the histogram from the unexposed border of the image was all the way to the left, picked the white balance point on this unexposed border, copied this profile to all the other frames, and found that unexposed border spike was in the same place in the histogram for every frame on the roll, and never split into separate peaks for R, G, and B. This saved a HUGE amount of tweaking. Some frames I did not even have to tweak, and the white balance did not go wonky even once.
The sun has just set, so now I am off to digitize a couple more rolls of film.
Edit:
I am attaching a photograph of the light source with no film (had increase the shutter speed a lot to keep it from clipping) and a photo of some unexposed developed film (did not have a whole frame). This is a film type I have not run into before.
The RGB panel I am using is this one: Amazon.com
with a custom diffuser to make the light uniform.
The settings I came up with for my light source for this film type are:
Film Red Green Blue Exposure
Unknown ?Q4185 81 19 99 0.4
DSC04574.ARW (81.4 MB)
DSC04578.ARW (81.6 MB)
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Thanks for supplying the images! Good to see you’re much happier with the procedure as well.
I’ve played a bit with your flower picture and I was somewhat surprised to see that I only got acceptable results when picking the White Balance on the bare film first and then keeping the Red ratio and Blue ratio in the Film Negative tool at 1.00. I only needed to adjust the Reference exponent en Output level to ensure the red channel doesn’t clip.
It doesn’t work at all when I pick the white balance from the light source and copy over the temperature + tint and then try to figure things out with the Red and Blue ratios. @rom9 Any guess as to why?
Here’s my pp3 to try for yourself:
DSC04578.ARW.pp3 (521 Bytes)
And the result:
Not perfect, but decent in any case.
My reasoning is that unexposed film is, by definition, black. Nothing in any image can be blacker than unexposed film. Also by definition, over exposed film must be white. I don’t always get an over exposed part of an image, but the way I am capturing the frame, I always get a bit of unexposed film. This is always one of my neutral points when I select two neutral points in an image. For the other, I usually pick a white shirt, or clouds, or white water. Then select the white balance to the unexposed film. This gets me adequate results for my purposes. My aim is to get a jpeg quickly that gives a good idea of what is in the picture. If someone wants to print one of the pictures I scanned, they should go back to the raw image and spend more than the 30 seconds I spent on it to get a better conversion. BTW, this is what I got for that whole picture:
I added tags to the thread because the title tells us “absolutely nothing” . Feel free to change them.
If one REALLY wanted to maximize DR - they could bracket their shots digitizing the negative and then use hdrmerge to create a high dynamic range capture.
As others have mentioned, using “alternative” backlighting would require a profile designed for that backlight - which might be difficult since ColorCheckers are reflective and not transmissive, unless the backlight is bright enough to illuminate a ColorChecker in a VERY dark room.
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This might be a little tldr for me to read all, but loading a raw file and setting it to neutral is doing nothing for all intents and purposes. The white balance is set to ‘in camera’. No brightening, no base curve, no contrast… Nothing. Way less processing than possible with Lightroom for example.
And more importantly, a lot or people did good film scans with it so it can’t be limiting there.
You realize that inverting film negative consists of choosing black and white levels. if you leave that up to an auto-detect guess, then you will get different results.
If you shoot a whole roll with the exact same exposure settings (no auto exposure) then results should be predictable.
Are you sure you’re not clipping the raw data? Remember that the tools in your camera are pretty much useless. Really try shooting a piece of clear filmstrip (or leader) and looking at the raw histogram to make sure none of the channels are close to clipping. Then use the same exposure settings across the roll.
Don’t bother setting white balance in the camera. It has no use in capturing raw data.
Try in raw therapee setting the white balance to either the filmstrip, or the light source (but your light source must not be clipping then). Experiment for yourself what works.
The reason I created this thread is that the release version of RawTherapee was giving me randomly variable results, even when I tried to nothing to the loaded file the results were wildly different from frame to frame. I was trying to get control of the process. I wanted to be able to load a file and always get to a known starting point. I wanted the software to be predictable. It was not.
The dev version of the software entirely fixes the lack of control that I was experiencing with the released software. I don’t mind bad results when I am the cause of the bad results, but when I feel that nothing I do has any bearing on the results I’m getting I get frustrated because there is no path to get any better.
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Unfortunately, i have no idea 
I also did some experiments with non-white backlight from an rgb panel, but not enough yet to figure out a general rule to get consistent results.
True, i never tried but this might work.
@DAP In fact, i forgot to mention a very important feature in my previous post: the new version of the filmneg tool, also works on TIFF/PNG images, and not only on camera raw files as the previous version.
So, one can also apply the inversion after some custom preprocessing 
Good to hear, though I am unlikely to use it on anything but RAW images, and only until I run out of my parents negatives, (though my brother is threatening to give me all his negatives). I will keep the RAW files around in case I, or someone after me, wants to try and do a better job of converting the negatives than I did.
After viewing more than 100 rolls of negatives, and thousands of slides (much easier to digitize), I’d never go back to film. The number of pictures I’ve run into with scratches, embedded dust, light leaks, age degradation etc. it really makes me appreciate digital images. Even when the negatives are in perfect condition, the film grain makes them noisy and limits the resolution obtainable on 35mm film. That and not knowing if you got the picture for several days (1 hour photo is a thing of the past, and even that was too long) means you can’t re-take it if you find out that you screwed it up.
I don’t know of any archival media for digital yet, but since one can make perfect copies easily, it means I can safely transfer the data to new media as it becomes available, and keep multiple copies in different locations. The hard part is getting the digital data from the analog originals in the first place.
Film is easily damaged in handling, and decays even when it is left untouched. I will never understand the nostalgia for film.
I am very happy that RawTherapee is supporting film negatives. I have been putting together the pieces to digitize my families negatives since 2017. Buying a 3D printer was the critical piece that made me believe I could achieve the system, and RawTherapee was the last piece of the puzzle that made it possible.
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Yup. I’ve been wanting to digitize my old negatives for a while. My first attempt with my camera mounted on a normal tripod and darktable was a massive failure.
My second attempt with stuff I’d already digitized and an early version of @rom9 's module was much better.
I’ve been procrastinating on what is likely to be the third (and hopefully final) attempt - a copy stand based on the design @troodon posted a year or two ago, and this module. Maybe this weekend?