Perfect colour negative film conversions with GIMP and RawTherapee!
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- Опубліковано 18 жов 2024
- IMPORTANT UPDATE!
Since recording and publishing this video, I've experienced a few inaccurate conversions with some my old negatives. Further investigation has revealed the cause (I'm a little annoyed with myself for missing it) and, as a result, I've refined the process very slightly:
When the raw file is loaded into GIMP - which in turn loads it into RawTherapee automatically - it's essential to un-check "Clip out-of-gamut colours" (the very first item in the Exposure section). If this box is checked (which is the default), it's possible - though not always the case - that the colours in the negative won't be true to what was captured by the camera, and the inverted image in GIMP may have a colour cast (the very thing we're trying to avoid!). So, please uncheck the box as directed, and it will work correctly!
I also recommend setting Saturation to +10 in RawTherapee before the Colour Toning step, as this ultimately results in better saturated positives - but you can always add saturation when conversion is complete, if required...
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Converting B&W film negatives is easy, but if you've tried to convert colour negatives in Photoshop, GIMP and other similar tools, you'll know how difficult and frustrating it can be to achieve realistic colours and tones. There's always a colour cast to get rid of, requiring endless fiddling with curves, colour balance, layer masks etc. - and it never seems to produce an entirely satisfactory result.
Darktable and RawTherapee have their own negative conversion modules, but they produce variable and somewhat unpredictable results depending on image content (range of tones, border, sprocket holes etc.). Negative Lab Pro plug-in for Lightroom usually does an excellent job, though not always perfect - and it takes a level of direct control away from the user, hiding what's going on under the hood through automation and presets.
This video demonstrates my personally-developed method for converting colour negatives using GIMP 2.10 and RawTherapee 5.8. It requires a little more time and effort than automated tools such as Negative Lab Pro, but produces consistently good and - most of all - highly predictable results that remain entirely within the user's control. With a little practice, it should take around 2 to 3 minutes from loading a negative to exporting the finished positive. That's a couple of hours work or less for a 36 exposure roll, including a coffee break ;)
Key aspects of this approach and why it works so well include (1) applying a linear tone curve, (2) using the camera's white balance, (3) selecting the correct colour input profile, and - most importantly - (4) correcting the film base colour cast BEFORE negative-to-positive conversion and tonal adjustments. Correcting the film's colour cast before conversion is a much more effective method than using white balance and RGB curves adjustment later in the process, and essentially mimics the use of colour acetates or a dichroic head in traditional darkroom wet-printing.
Please try this... I think you'll like it!
Thanks for watching. If you find the video helpful, please click the "thumbs up" button to Like it, and leave a comment below! You could subscribe too, if you wish (but I may never post another video LOL)...
Have fun, stay safe, and best wishes,
Mike
(BigMackCam @ PentaxForums)
I’m almost never commenting on anything on UA-cam but I want to share my appreciation for this workflow :) film inversion was one of the last things that prevented me from fully switching to Linux - it’s why I kept my Mac with Lightroom and NLP. Your workflow can be done on Linux and produces great results! Only in one case I experienced some channel clipping but it may have been a scanning issue
Since recording and posting this video, I've refined the method slightly. When the negative loads into RawTherapee, you should un-check the Clip out-of-gamut colour box (the first item in the Exposure section). I also recommend setting Saturation to +10, as this results in better saturated positives later in the processing. Both these steps should be carried out BEFORE the Colour Toning correction for the film base...
I will try that. Im still trying to nail down the formula to get my dslr scans looking like my lab scans off an older roll. Then I'll know my hand dev'd rolls will be pretty representative going forward.
it worked beautifully. thanks a lot. it must have taken a while to figure out this approach. i improvised with a 85 mm prime + 26 mm extension tubes to get about 1:2 magnification (about 1.6 required to cover a 35mm film with aps-c sensor). the depth of field was good enough to cover the film plane and i got good sharpness in the center and corners
You're most welcome! I'm so pleased it worked well for you... and nice job with that improvised lens plus extension tube setup! 🙂
you're a true artisan and a genius! This is so cool
I didn't end up doing it the way you did, however, a couple of interesting steps I'm incorporating into my workflow. Using the tonal adjustment slider to match the border %s before you even invert? Interesting touch. Thanks!
Great Tutorial, Thank You! My results so far have been amazing and it would be great if it were able to be automated and turned into a batch file so lots of neg's could be done this way. Just one note, for such a thorough tutorial, the step regarding linking Raw Therapee to Gimp took me a while to work out through other sources. Would be handy to mention in your video that the 2 programs need to be linked. Cheers.
Thanks for the positive and constructive feedback! Great to hear you're happy with the results from this method. Your point regarding initial setup of the tools - specifically, configuring GIMP to use RawTherapee as the raw tool - is a good one. I'm in the process of building a personal website which will include an updated version of this tutorial with several improvements, and I'll aim to include more information on tool config. Thanks for the tip - much appreciated 😃
Amazing advice! My negative film scans had never before seemed as good. Thank you very much. I use Vuescan with an Epson 4990.
And thank *you* for the nice feedback! I'm so glad this method has worked out well for you. Recently I've made some improvements that result in even better colour accuracy (not greatly so, but depending on the individual negative it can make a noticeable difference). I'll make a new video when I get a chance, or possibly create a dedicated website. Watch this space!
@@bigmackcam4242 That's wonderful. I'm excited about it. Due to a lack of this priceless information that has helped revitalize my photo collection, I had nearly given up scanning a sizable number of negatives for decades. It appears that the greenish tint will be removed from childhood images of my children, revealing their actual hues for the first time. I'm very happy I came across your video.
@@nghin4vacsf What a heart-warming reply - thank you so much, I really do appreciate your kind words. Actually, you've made my day... Family negatives are important memories, and if this method enables you to produce better conversions from them, I couldn't be happier. Best wishes!
Thank you! It works great, I just started shooting color and I was little bit disheartened with the results. Besides 'out of gamut' and 'saturation' from your comment, did you change your process since this video was posted? ?
This was really useful! thanks for posting it
amazing work this is extremely impressive
Thank you very much for the great feedback! I hope to do a revised video in the not-too-distant future incorporating the updates mentioned, and showing how the same results can be achieved with Darktable rather than RawTherapee for those who prefer it.
I was doing good until I clicked on the order of the negative and went to pull that bar across to equal the values, but there were no values showing where I kicked the border of the negative, liking your case you had a little bubble that the three values were showing well. I don’t get that on mine and I can’t figure out why I have the same version as you
You have to turn it on, there is a little symbol besides color toning
@@jasolt4372 thanks
Have you tried this method yet? If so, please let me know how it worked out for you! An essential part of the workflow is setting the camera's white balance to the light source before digitising the negative. This enables accurate reproduction of the film base colour in RawTherapee, allowing precise correction using the Colour Toning tool. The end result is a positive with no unnatural colour cast...
Thank you very much for this tutorial, I've just tried it once, a few minutes ago, and the result is very good, but for the particular image I tried, I got better results with Darktable/Negadoctor, particularly on the skin tones, will keep trying though, it's still MUCH better than the RawTherapee provided "Film Negative" tool (go figure) :) cheers.
PS: The image I tried is a night picture with flash, and yes, the film is about 20 years old.
@@EstebanFonsecaAR You're welcome :) I've used RT's "Film Negative" and Darktable's "Negadoctor" tools extensively, and find that both *can* produce good results - but they're not as consistent as the approach I've outlined. That's been my experience when working with a range of negatives from different film stock. I'd encourage anyone to use what works best for them :)
I've just ran a quick test, and matching the RGB values on the unexposed film area, gives the same result as doing a custom white balance on that area, and is quicker. The end result in GIMP is the same.
That *can* happen, but it isn't consistent and is dependent on the tonal content of each image. I have some negatives where auto or custom white balance produce very similar output to manual colour correction, and others where the results are quite different. If custom white balance works for you, go for it - but my own experience is that manual colour correction is much more consistent...
Have you also tried the "Film Negative" in Rawtherapee without GIMP?
Seems like I can't click the camera standard button it's just dark and unclickable any idea why?
Is it possible that you've loaded a TIFF or JPEG file rather than raw? If that's the case, switch to using raw; and my preference here is to use .DNG format if available, as opposed to the camera manufacturer's own native raw file format (e.g. ARW for Sony, PEF for Pentax, etc.). However, if you're already using DNG format and still can't select RawTherapee's Camera Standard profile when using those files, perhaps your camera model isn't currently supported. I'd be pretty surprised, but it's possible. May I ask what camera you're using?
@@bigmackcam4242 yeah it was definitely a jpeg thanks for your help didn't even know if you would reply really appreciate it thanks for the useful video
@@bigmackcam4242 Subd!
@@Graysonemory Right, that explains it 🙂 Just for your info and anyone else reading, the reason you can't select the Camera Standard profile in RawTherapee for a JPEG (or, indeed, a TIFF) is that the profile has already been applied in-camera. By the time the camera spits out a JPEG, the colour profiling choices are baked in. Glad you found the video useful, and many thanks for the kind feedback 🙂
@@bigmackcam4242 ahhh so a raw file is more moldable per se?
For me, the result is not very impressive. The final photo came out with an unnatural color cast, but the workflow itself is interesting.
Thanks for the feedback!
There are several reasons why you might see a colour cast when using this method. I've listed them below, with solutions in parentheses:
1) The digital capture of the negative wasn't correctly exposed, with either highlights or shadows clipped (use over- and under-exposure warning on the camera to assist, and adjust exposure so the histogram distribution is approximately central)
2) White balance problem (set camera white balance against the light source prior to capture, and ensure white balance is set to Camera in RawTherapee)
3) The incorrect input profile was selected in RawTherapee (select Camera Standard)
4) A non-linear tone curve was applied (ensure Tone curve 1 & 2 are set to linear / standard)
5) "Clip out-of-gamut colours" box in RawTherapee was checked (make sure it's unchecked before the colour correction step)
6) "Highlight reconstruction" option in RawTherapee was selected (make sure it's unchecked before the colour correction step)
7) Strong colour noise in the digital capture (use base ISO to capture the negative, and optionally activate Noise Reduction in RawTherapee before the colour correction step)
8) Light leaks in the camera caused partial exposure in the border of the photo, and this area was sampled for colour correction (select a different area of the border)
9) The backlight source used to illuminate the negatives has a poor CRI or extreme colour temperature (use a high CRI light source with 5000 - 6500K colour temperature)
10) The film has aged. Colour negative film isn't generally considered archival media. Individual colour layers degrade at different rates over time, leading to a genuine colour imbalance (no solution to this one, other than to adjust colour balance after conversion)
I've tested and refined this method extensively, and used it to convert numerous negative films from different stock. If it's followed to the letter, the only time it should result in a colour cast is if that cast is actually there - which is often the case with poorly-stored / aged film... (i.e. it's not a fault of the conversion method).
I hope this helps!
@@bigmackcam4242Thanks for the comprehensive answer.
@@androman4085 You can also try Darktable and the Negadoctor tool that comes with it. I've found that for some negatives I get better results with Darktable and for other negatives RawTherapee is better. Also, the "Auto input levels" on Gimp is not always the best option, you can try on the "Levels" tool stretching the histogram first (The top slider, remove the flat/empty section on both hightlights and shadows), and comparing the results.