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A Better Light Source for Scanning Color Negative Film

285 points by eloisius 2y ago

turnsout 2y ago
Productize this! Plenty of people would pay between $200—600 for this.
findthewords 2y ago
This might explain why some new film scans on blu-ray look the way they do. Green-yellowish and strange.
- KaiserPro 2y ago
  Blue-rays would have been either done by telecine https://www.ebay.co.uk/itm/283479247780 https://www.ebay.co.uk/itm/283479247780 (From what I recall its nominally a real time machine). That used flourecent light sources (although I never worked on it, so that could be a lie.) or by this https://www.filmlight.ltd.uk/products/northlight/overview_nl.php https://www.filmlight.ltd.uk/products/northlight/overview_nl... a non realtime scanner with "perfect" registration. Again I can't remember the light source, but I suspect its probably an arc gap like large projectors. I do know that it has a massive cooling chamber to make sure it doesn't heat the film though. That scanner is a non-realtime CCD slit scanner.
  - jamesfmilne 2y ago
    We offered an LED light source for both Northlight 1 and 2 as an upgrade over the previous metal halide bulb light source. https://www.filmlight.ltd.uk/pdf/datasheets/FL-NL-DS-0566-NLLEDLight.pdf https://www.filmlight.ltd.uk/pdf/datasheets/FL-NL-DS-0566-NL...
    - KaiserPro 2y ago
      sweet, I used to work at framestore(cfc) next to where the scanning lab was. I really liked watching the raw scans pop up
Palomides 2y ago
doesn't this depend on matching the leds closely to the sensor? I'm not aware of camera manufacturers publishing details on the wavelengths their sensors respond best to maybe close enough is fine for this, though
- estebank 2y ago
  > I'm not aware of camera manufacturers publishing details on the wavelengths their sensors respond best to It is relatively easy to experimentally find this out https://nikongear.net/revival/index.php?topic=10662.0 https://nikongear.net/revival/index.php?topic=10662.0
- flimsypremise 2y ago
  Yes, you do actually need to do this. You basically need to calibrate every sensor to ensure that the correct wavelength of light ends up in the right channel.
- jackw01 2y ago
  All that really matters is that the red and blue wavelengths are far out enough to not overlap with the magenta dye layer on the film or the green channel on the camera sensor.
tecleandor 2y ago
I don't know if the creator is around here, but I guess if there's anything to consider on the proportion of green, blue and red power to adjust the curves. I think I still have an spectrophotometer around to check that...
- JKCalhoun 2y ago
  I'm confused that in a diagram on the page, the BGR LED frequencies (particularly R) don't seem to all align with the peak sensitivity frequency of the film. It still seems like you would want a broader sampling of light. Post-processing, regardless of the math involved, is cheap.
  - jackw01 2y ago
    "sensitivity" or density? The light source wavelengths don't need to align with the density peaks of the film, they just need to be far enough apart to isolate the individual dye layers and avoid the overlap between the camera sensor channels. Using 700nm for red would be challenging as most digital camera sensors aren't all that sensitive to 700nm.
KaiserPro 2y ago
Personally I have found that using LED film softlights to be useful for scanning. I didn't have the time to do what this wonderful article does, which is research, design and build a decent softlight source. In the old days, you might have been able to use a florescent 5600k light sources, as rated ones have a known spectrum that can be counted on. Having those in a light table would get you 90% of the way to a decent scan. One thing I did note is that the second colour image appears to have nowhere near the aliasing or film noise of the first sample. Was its scanned at different settings?
- pixelfarmer 2y ago
  I used a primitive setup: Flashlight mounted on camera and "guided" to the back of the negative, so not even remote flashlight because I didn't have that for the camera. I used Darktable for the conversion process and there were 3 key points: Exposing the negative to fully exploit the RAW channels of the camera, setting a proper black and white point in the conversion process, apply white balance as needed and maybe manually tune the green/magenta slider a bit. Usually, if all that went well, I received pretty clean results. If something got botched in the process, I would see the same noise as the top right image shows. As the article notes the resulting dynamic range is really low then, which makes noise pop out. Noise is also in the bottom right example image, but the larger resulting DR (and downscaling) hides it well enough.
CrispyKerosene 2y ago
Amazing write up and research - We need more of this! My feeling is most people who are going to be interested in the slight increase in color accuracy are already drum scanning or using a virtual drum scanner like a Imacon flextight, and the team at Imacon has some crazy color scientists working on that as evidenced by the images it outputs. The quest for the most true colors from C-41 feels like a pointless exercise in ways. When i print RA-4 in the darkroom i am working with a set of color correction filters and spinning dials to mix color on my enlarger head. The resulting print is my interpretation of the negative. Back in the 1-Hour-Photo Minilab days, the tech was doing more or the less the same thing as well, or just hitting 'auto' and the Noritsu or Frontier was making adjustments to each frame before printing it. If i am scanning the negatives with a camera and light source and after inverting, a greenish mask is still present, as like in the first conversion example they give, a few tweaks of a few sliders in photo editing software is enough to correct it. The bigger factor at play here in my mind, is the availability of robust and consistent color developing services. Most indie labs these days are using C41 kits and at best a Jobo machine. There are very few labs even offering Dip and Dunk with a proper replenishment cycle with chemistry from the big players like Fujihunt or Kodak Flexicolor. A a half a degree off temp, or a developer that near its rated capacity is enough to megafuck the resulting negatives. There is an even worse trend of indie chemistry manufactures offering C41 kits with seemingly innocent replacements, that have huge consequences. For example one indie manufacturer in Canada is shipping there kits without a proper Color Developer (CD4) and instead using p-Phenylenediamine, which guarantees the incorrect formation of dyes Sorry if i sound negative and got on a rant, i really do love this sort of research.
- shiftpgdn 2y ago
  Drum scanning is crazy time consuming and expensive. I shoot hundreds (sometimes thousands) of film photos per year and 99.999% of my scanning is done with a camera and a backlight.
  - gorgoiler 2y ago
    Cross polarised light (to eliminate specular reflection) and a home made vacuum bed is 99% of the way to a seriously pro scanning tool. A setup like that helped me get through 15k prints in no time with excellent results. The biggest barrier to success was after churning through the 7x5 and 6x4 shots, things got a lot harder with variable sizes of print. It really slowed the process down — and conversely, uniform print sizes made the first 90% of the job almost enjoyable. I averaged one “scan” every 2s.
zokier 2y ago
If you want to get serious on this, get good quality color chart[1] and use that to compare different light sources etc. Just eyeballing resulting colors from random photos and guesstimating the various spectral curves gets you only so far. [1] e.g. https://www.silverfast.com/products-overview-products-company-lasersoft-imaging/it8-targets-for-scanner-calibration-profiling-for-predictable-brilliant-colors/ https://www.silverfast.com/products-overview-products-compan...
- dvdkon 2y ago
  Yes, but you'd want that colour chart on the type of film you're scanning, for reasons explained in the OP. Sadly all I found in a brief search were calibration targets on slide film, not negatives.
  - musictubes 2y ago
    Back in the early 90s I used a Noritsu printer. We had reference negatives on all the different film stocks, or at least all the ones we regularly saw there. We would group the jobs by film type. Set the calibration by the calibration negative and judge exposure and basic color correction by direct viewing of the negative. Another person would check the prints and flag any that needed to be redone for color, dust, exposure, etc. Then we’d change film types. The next time I touched a photofinishing machine in the early 2000s you looked at a screen to make adjustments and we offered digital services like scanning and printing from digital files. I still used my negative reading skills to talk to customers when we were troubleshooting results. Putting the negative on the light table to show them how thin they were or how wildly the color changed when you switched what kind of light the picture was shot in was the quickest way to resolve quality complaints.
  - zokier 2y ago
    I'd imagine that just grabbing the reflective target and shooting it yourself on film would get decent results? Assuming the target patches have good spectral coverage
fallinditch 2y ago
I'm planning to do some negative scanning with a phone or iPad as a light source. I know I'll have to make some simple tweaks to the color balance of the scans. I believe it is totally normal to have to make some adjustments to scans, the side by side example in the article seems to show that a white light source is perfectly fine for this work. It's unlikely that an RGB light source would produce scans that don't require any adjustments, so I'm failing to see the benefit.
- deleted 2y ago
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- cedricd 2y ago
  I've scanned a few hundred images using an iPad as the light source. I've tried both a white screen and a bluish screen designed to basically invert the orange cast from the negative. Both seem to work well. The bluish thing works quite well, but it turns out that different rolls need slightly different light color to compensate, so it wasn't worth the trouble. In the end the best result was buying a license for Negative Lab Pro[0] to post process everything [0]: https://www.negativelabpro.com/ https://www.negativelabpro.com/
  - fallinditch 2y ago
    That's a good recommendation, thank you. It's amazing how complicated film photography has become in the digital era! My next task is to ditch Lightroom/Photoshop subscription. I'm going to give Darktable a go. Edit: aaah, I see NegativeLabPro needs Lightroom, hurrumph...
  - kosma 2y ago
    Seconded. NLP is well worth the money - not just in results, quality, and time saved, but also in finding joy in shooting and scanning color.
  - tsaiDavid 2y ago
    I held out for sometime myself, but NLP is excellent. It works particularly well with an old Pakon I still use as well as using a camera to “scan”.
zackmorris 2y ago
Even after working with colorspaces for decades in Photoshop and various game dev tools, I find color conversion mystifying. I've studied all of the equations and given it my best effort, but would not bet real money that the colors I'm displaying are close to real life. It's like the game of telephone, I just can't trust so many steps. So for this article, I don't see mathematical proof that the negatives have been inverted accurately, regardless of method, even though I'm sure the results are great. I suspect it comes down to subjective impression. Here's a video I found discussing monitor calibration: https://www.youtube.com/watch?v=Qxt2HUz3Sv4 https://www.youtube.com/watch?v=Qxt2HUz3Sv4 If I could fix everything, I'd make all image processing something like 64 bit linear RGB and keep the colorspace internal to the storage format and display, like a black box and not relevant to the user. So for example, no more HDR, and we'd always work with RGB in iOS instead of sRGB. Loosely that would look like: each step of image processing would know the colorspace, so it would alert you if you multiplied sRGB twice, taking the onus off of the user and making it impossible to mess up. This would be like including the character encoding with each string. This sanity check should be included in video card drivers and game dev libraries. If linear processing isn't accurate enough for this because our eyes are logarithmic, then something has gone terribly wrong. Perhaps 16 bit floating point 3 channel RGB should be standard. I suspect that objections to linearity get into audiophile territory so aren't objective. For scanning color negatives, the brand of film would be mapped to a colorspace, the light source would have its own colorspace, the two would get multiplied together somehow, and the result would be stored in linear RGB. Inversion would be linear. Then the output linear RGB would get mapped to the display's sRGB or whatever. My confusion is probably user error on my part, so if someone has a link for best practices around this stuff, I'd love to see it.
- lcrs 2y ago
  Colour in the Photoshop/gamedev world is often handled pretty casually, but if you're interested the moving picture world gets a lot more rigorous about it and there's tons of documentation around the ACES system in particular: https://github.com/colour-science/colour-science-precis https://github.com/colour-science/colour-science-precis https://acescentral.com/knowledge-base-2/ https://acescentral.com/knowledge-base-2/ As you suggest storage in linear 16-bit float is standard, the procedure for calibrating cameras to produce the SMPTE-specified colourspace is standard, the output transforms for various display types are standards, files have metadata to avoid double-transforming etc etc. It is complex but gives you a lot more confidence than idly wondering how the RGB triplets in a given JPG relate to the light that actually entered the camera in the first place...
keepamovin 2y ago
This is cool. The original looks kinda green to me. Awesome.
alnwlsn 2y ago
Anyone know if this is the right technique to use on 8/16 mm movie film (which is a positive instead of negative)? Modifying an old projector to go one frame at a time is the easy part, but you can't use the original halogen bulb since it will burn a hole right through the film at that speed.
- Finnucane 2y ago
  Yeah, it would be interesting if this makes much of difference for slide film, either e-6 or Kodachrome (I am old and have both).
  - tecleandor 2y ago
    In the article they say that for positive film (slides, at least) white light is generally better than rgb, but it would be nice to test it.
    - Finnucane 2y ago
      Missed that. I guess that makes sense, since those films are designed for projecting more than printing.
- smogcutter 2y ago
  There are also rotoscoping and analysis projectors designed to hold on a frame.
- qingcharles 2y ago
  I scanned a lot of positives on an Epson V850 flatbed just fine. Except for the resolution and the setup being a bit finicky, there wasn't much between that and the $25K X5 scanner I had.
felixhandte 2y ago
Awesome work! I get exactly that green cast and muted color range off of my flatbed scans (Epson v800). This is a really intriguing path to fixing them I hadn't considered. It seems like the writeup here doesn't specify what you're using for the actual imaging? A flatbed scanner? A camera?
esafak 2y ago
After all that work I was expecting a chromaticity diagram to demonstrate the expanded gamut, but nice job regardless.
- flimsypremise 2y ago
  RGB scanning doesn't actually expand the color gamut, but removes erroneous color information. If you use white light you end up recording color information from the dyes in wavelengths outside of those that RA-4 paper is sensitive to, and which the color engineers who designed the film never intended it to be used with.
  - esafak 2y ago
    Thank you for the correction. Then you can measure the color difference?
    - flimsypremise 2y ago
      Yes, there's actually a very good test for a properly inverted color negative. You need a negative of a greyscale step scale from light to dark. If the color channels are properly linear relative to one another in the scanned image, you should be able to white balance any one of the patches and have all of the others remain neutral: by which I mean each patch should have equal amounts of red blue and green. In practice the characteristic curves of film often mean the darkest and lightest patches are often slightly more green or red, but its very close. So the process would be, using the RAW scan of the image (the orange mask intact): 1) Invert the image. 2) White balance on any patch. 3) Sample the color balance of every other patch. They should have equal amounts of all colors.
- deleted 2y ago
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assimpleaspossi 2y ago
Looking at the results, it looks to me that the print with the white light has far more detail while the RGB print has washed out ground under the tower.
- pimlottc 2y ago
  Yeah, it's not clear to me either that the RGB image is obviously better, especially without knowing that actual conditions were like when the photo was taken. Perhaps the author could explain why they find one image superior instead of just putting two images side-by-side, with the implied message that "any idiot can see that <x> is better".
throw0101b 2y ago
> White light scan captured using 95+ CRI 5000K light source. RGB scan captured using custom 450nm+525nm+665nm light source. While high-CRI is better than low(er)-CRI, one criticism is that the 'score' is somewhat lacking in it measure an important component: > Ra is the average value of R1–R8; other values from R9 to R15 are not used in the calculation of Ra, including R9 "saturated red", R13 "skin color (light)", and R15 "skin color (medium)", which are all difficult colors to faithfully reproduce. R9 is a vital index in high-CRI lighting, as many applications require red lights, such as film and video lighting, medical lighting, art lighting, etc. However, in the general CRI (Ra) calculation R9 is not included. […] > R9 value, TCS 09, or in other words, the red color is the key color for many lighting applications, such as film and video lighting, textile printing, image printing, skin tone, medical lighting, and so on. Besides, many other objects which are not in red color, but actually consists of different colors including red color. For instance, the skin tone is impacted by the blood under the skin, which means that the skin tone also includes red color, although it looks much like close to white or light yellow. So, if the R9 value is not good enough, the skin tone under this light will be more paleness or even greenish in your eyes or cameras.[25] * https://en.wikipedia.org/wiki/Color_rendering_index#Special_value:_R9 https://en.wikipedia.org/wiki/Color_rendering_index#Special_...
twic 2y ago
The thing i found most interesting here is the brightness enhancing film: https://newhavendisplay.com/blog/brightness-enhancement-film-bef/ https://newhavendisplay.com/blog/brightness-enhancement-film... Basically, it's a collimator: it takes light going in all directions (eg from a lamp), and turns it into light all going in one direction. What does it look like to look through? Do objects appear brighter? I suppose they appear brighter but also smeared out?
- grvbck 2y ago
  > What does it look like to look through? Do objects appear brighter? I suppose they appear brighter but also smeared out? Pretty much exactly so: https://youtu.be/ugkjNPH1J-4 https://youtu.be/ugkjNPH1J-4
flimsypremise 2y ago
So I wrote an article about this a few years back and also developed a custom RGB light for my own scanning: https://medium.com/@alexi.maschas/color-negative-film-color-spaces-786e1d9903a4 https://medium.com/@alexi.maschas/color-negative-film-color-... There's also some proper academic research into this subject going on currently: https://www.researchgate.net/publication/352553983_A_multispectral_design_for_a_new_generation_of_film_scanners https://www.researchgate.net/publication/352553983_A_multisp... One thing that's important to note about this process is that the idea is not to _image_ the film, but rather to measure the density of each film layer and reconstruct the color image from that information. This is a critical realization, because one of the most important things to know about color negative film is that the "color" information in the negative actually only exists relative to the RA-4 printing system. Negatives themselves don't have an inherent color space. Cool to see someone else working on this though. I actually considered those drivers for my build, but I ended up building a very high frequency, high resolution PWM (30khz/10bit) dimming solution with TI LM3409 drivers. It's very hard to get uniform light as well so I ended up getting some custom single chip RGB LEDs. https://i.imgur.com/BVM9p6Q.jpeg https://i.imgur.com/BVM9p6Q.jpeg https://i.imgur.com/5oozHnN.jpeg https://i.imgur.com/5oozHnN.jpeg I've been working on this for a few years, and what I will say is that there's actually another level of complexity beyond just implementing the light. There's a lot of testing to ensure that you're getting proper linearization of each channel, and there's still a color crosstalk problem arising from the misalignment between the color sensitivity of most modern digital cameras and the bands that are used to scan color negatives. It requires some additional tweaking to get all of the color information in the correct channel. You can also very easily end up saturating a channel without realizing it as well. Oversaturated reds are a common occurrence in RGB scanning. I'd also note that the wavelengths you should shoot for are more along the lines of 440nm 535nm 660nm, which correspond to the Status M densitometry standard. This standard was designed specifically for color negative film.
- m463 2y ago
  Is there a way to process dust/scratches? Like wavelengths outside the chosen r/g/b range?
  - 2y ago
hoherd 2y ago
Maybe it's because I'm colorblind, but the top-right image looks much better than the bottom-right image to me. Can somebody explain why the bottom-right image is allegedly superior? I know there's a write up about what's going on and all the science behind it, but what I'm asking about is what you as a person with color receptive vision sees that is better.
- realreality 2y ago
  The top photo has a blue-green cast, whereas the bottom photo has a magenta cast. Maybe the bottom one is a more realistic reproduction of the scene, but I also prefer the top one, which is more saturated and closer to what I associate as a film image. Each kind of film has its own character and color variations; it’s silly to try to neutralize everything.
- asimpletune 2y ago
  I looked at both before knowing which was which. Immediately I recognized the look of the top right photo, whereas the bottom right didn't quite seem to have "the look". So, I think it might be that it looks better to you because it looks more like how a photo looks. It's similar to how younger people may prefer 60fps or weird settings on TV shows that give it the "soap opera effect" vs how older people can't stand them. After switching back and fourth and really looking closely at each one I ended up deciding that I liked the bottom right photo, even though I could recognize the top right one had a more classic film look. For me it was just because there was more detail in the colors. The original scan was kind of washed out in the blues I guess, as well as being a little more red in the dirt area.
  - ralferoo 2y ago
    I too preferred the top right photo. Arguably, it has less detail in the tree line, the city is neither better or worse, just different, but for me the skyline and sky are far superior with the top right photo. Maybe this is prejudiced because this is how I remember old photos to be... But then, isn't that the point of scanning old negatives anyway - to recreate what the old images on them would have looked like at the time? Arguably though, the correct solution is to preserve the source information as much as possible, so similar to what it proposed - scan the images using light sources that correspond to the peaks of the chemicals used in the negative, and then colour grade directly from that using a modified inverted curve. Doing it that way should permit both outputs by changing the curves used in colour grading, and I suspect the real issue is just "inverting colours" isn't the most appealing visually, just as most professional photos are colour graded to some extent because the raw images don't look as appealing.
anfractuosity 2y ago
Interestingly that doesn't appear to mention infrared from a quick scan, which is used to help remove dust as far as I understand. (I've got an old Canon FS4000, which uses IR)
- m463 2y ago
  I scanned negatives long ago without IR and it was horrible. Dust and fiber were a major headache, especially when scanning lots of film. But since we're living in the future, I suspect we could make AI models that would work practical magic.
  - anfractuosity 2y ago
    Heh, yeah good point, I imagine that would work well too, didn't think of that.
  - eloisius 2y ago
    If AI was in the mix, regenerating my images, personally I wouldn’t bother with scanning, and I’d just go back to digital.
    - m463 2y ago
      All the scanned photos I've worked with were taken pre-digital.
deleted 2y ago
[deleted]
zokier 2y ago
Btw regarding the camera sensitivity, if you shoot raw and just shoot the different colors separately, you can mostly ignore the spectral characteristics of the sensor. Debayering might end up being very different than standard though.
mikewebkist 2y ago
It seems like an alternative would be a broad-spectrum white light source with narrow-band color filters that correspond to similar wavelengths to the LEDs mentioned. That would require simpler light source but more costly subtractive filtering. All those old-school minilabs pre-blue LEDs...they must have used white light sources and filters, right?
- xkcd-sucks 2y ago
  Being able to tune the intensity ratio of the bands, especially with source age, is nice so that everything's in the middle of the sensor's dynamic range ... optical filters can be pretty cheap at scale or as surplus, but, well behaved broadband light sources aren't so easy to find.
- jackw01 2y ago
  Author here, I was curious about this too since I would have expected most film scanners from the 90s-2000s to use incandescent light sources if high-CRI light was really the way to go. Minilabs that made direct optical prints to RA-4 paper did use white light sources with filters, since RA-4 paper is already only sensitive to narrow bands of light. In the mid-90s, Fujifilm and others introduced minilabs that could also scan film and produce prints from digital files. These all used RGB LEDs to scan the film, and they must have had a very good reason to since blue LEDs were barely ready for commercial use at the time.
strogonoff 2y ago
TL;DR Negative film is (obviously) intended not for viewing by humans, but for a specialized development process. Digital cameras are geared towards capturing images as humans would perceive them, and in regular photography using full spectrum light supposedly makes metameric failure less likely. Thus, it may appear counter-intuitive to a seasoned photographer that using a specific narrow band RGB lighting can be preferable when digitizing typical negative film, working around the use case mismatch and improving colour reproduction.
Animats 2y ago
Why not use a single monochrome sensor and just turn on R, G, and B lights for three images? Many flatbed scanners do that.
- mplewis 2y ago
  This saves a lot of time in post-processing.
coisasdavida 2y ago
Anyone knows a similar supplier in Europe I could source the parts from?
bijutoha 2y ago
The idea of using narrowband RGB light sources for scanning color negatives is fascinating. It’s great to see a practical approach that addresses the common issues with white light scans. I’m curious: have you tested this setup with different film stocks, and if so, how consistent were the results across various brands?

285 points by eloisius 2y ago

turnsout 2y ago

Productize this! Plenty of people would pay between $200—600 for this.

findthewords 2y ago

This might explain why some new film scans on blu-ray look the way they do. Green-yellowish and strange.

KaiserPro 2y ago
Blue-rays would have been either done by telecine https://www.ebay.co.uk/itm/283479247780 https://www.ebay.co.uk/itm/283479247780 (From what I recall its nominally a real time machine). That used flourecent light sources (although I never worked on it, so that could be a lie.) or by this https://www.filmlight.ltd.uk/products/northlight/overview_nl.php https://www.filmlight.ltd.uk/products/northlight/overview_nl... a non realtime scanner with "perfect" registration. Again I can't remember the light source, but I suspect its probably an arc gap like large projectors. I do know that it has a massive cooling chamber to make sure it doesn't heat the film though. That scanner is a non-realtime CCD slit scanner.
- jamesfmilne 2y ago
  We offered an LED light source for both Northlight 1 and 2 as an upgrade over the previous metal halide bulb light source. https://www.filmlight.ltd.uk/pdf/datasheets/FL-NL-DS-0566-NLLEDLight.pdf https://www.filmlight.ltd.uk/pdf/datasheets/FL-NL-DS-0566-NL...
  - KaiserPro 2y ago
    sweet, I used to work at framestore(cfc) next to where the scanning lab was. I really liked watching the raw scans pop up

Palomides 2y ago

doesn't this depend on matching the leds closely to the sensor? I'm not aware of camera manufacturers publishing details on the wavelengths their sensors respond best to maybe close enough is fine for this, though

estebank 2y ago
> I'm not aware of camera manufacturers publishing details on the wavelengths their sensors respond best to It is relatively easy to experimentally find this out https://nikongear.net/revival/index.php?topic=10662.0 https://nikongear.net/revival/index.php?topic=10662.0
flimsypremise 2y ago
Yes, you do actually need to do this. You basically need to calibrate every sensor to ensure that the correct wavelength of light ends up in the right channel.
jackw01 2y ago
All that really matters is that the red and blue wavelengths are far out enough to not overlap with the magenta dye layer on the film or the green channel on the camera sensor.

tecleandor 2y ago

I don't know if the creator is around here, but I guess if there's anything to consider on the proportion of green, blue and red power to adjust the curves. I think I still have an spectrophotometer around to check that...

JKCalhoun 2y ago
I'm confused that in a diagram on the page, the BGR LED frequencies (particularly R) don't seem to all align with the peak sensitivity frequency of the film. It still seems like you would want a broader sampling of light. Post-processing, regardless of the math involved, is cheap.
- jackw01 2y ago
  "sensitivity" or density? The light source wavelengths don't need to align with the density peaks of the film, they just need to be far enough apart to isolate the individual dye layers and avoid the overlap between the camera sensor channels. Using 700nm for red would be challenging as most digital camera sensors aren't all that sensitive to 700nm.

KaiserPro 2y ago

Personally I have found that using LED film softlights to be useful for scanning. I didn't have the time to do what this wonderful article does, which is research, design and build a decent softlight source. In the old days, you might have been able to use a florescent 5600k light sources, as rated ones have a known spectrum that can be counted on. Having those in a light table would get you 90% of the way to a decent scan. One thing I did note is that the second colour image appears to have nowhere near the aliasing or film noise of the first sample. Was its scanned at different settings?

pixelfarmer 2y ago
I used a primitive setup: Flashlight mounted on camera and "guided" to the back of the negative, so not even remote flashlight because I didn't have that for the camera. I used Darktable for the conversion process and there were 3 key points: Exposing the negative to fully exploit the RAW channels of the camera, setting a proper black and white point in the conversion process, apply white balance as needed and maybe manually tune the green/magenta slider a bit. Usually, if all that went well, I received pretty clean results. If something got botched in the process, I would see the same noise as the top right image shows. As the article notes the resulting dynamic range is really low then, which makes noise pop out. Noise is also in the bottom right example image, but the larger resulting DR (and downscaling) hides it well enough.

CrispyKerosene 2y ago

Amazing write up and research - We need more of this! My feeling is most people who are going to be interested in the slight increase in color accuracy are already drum scanning or using a virtual drum scanner like a Imacon flextight, and the team at Imacon has some crazy color scientists working on that as evidenced by the images it outputs. The quest for the most true colors from C-41 feels like a pointless exercise in ways. When i print RA-4 in the darkroom i am working with a set of color correction filters and spinning dials to mix color on my enlarger head. The resulting print is my interpretation of the negative. Back in the 1-Hour-Photo Minilab days, the tech was doing more or the less the same thing as well, or just hitting 'auto' and the Noritsu or Frontier was making adjustments to each frame before printing it. If i am scanning the negatives with a camera and light source and after inverting, a greenish mask is still present, as like in the first conversion example they give, a few tweaks of a few sliders in photo editing software is enough to correct it. The bigger factor at play here in my mind, is the availability of robust and consistent color developing services. Most indie labs these days are using C41 kits and at best a Jobo machine. There are very few labs even offering Dip and Dunk with a proper replenishment cycle with chemistry from the big players like Fujihunt or Kodak Flexicolor. A a half a degree off temp, or a developer that near its rated capacity is enough to megafuck the resulting negatives. There is an even worse trend of indie chemistry manufactures offering C41 kits with seemingly innocent replacements, that have huge consequences. For example one indie manufacturer in Canada is shipping there kits without a proper Color Developer (CD4) and instead using p-Phenylenediamine, which guarantees the incorrect formation of dyes Sorry if i sound negative and got on a rant, i really do love this sort of research.

shiftpgdn 2y ago
Drum scanning is crazy time consuming and expensive. I shoot hundreds (sometimes thousands) of film photos per year and 99.999% of my scanning is done with a camera and a backlight.
- gorgoiler 2y ago
  Cross polarised light (to eliminate specular reflection) and a home made vacuum bed is 99% of the way to a seriously pro scanning tool. A setup like that helped me get through 15k prints in no time with excellent results. The biggest barrier to success was after churning through the 7x5 and 6x4 shots, things got a lot harder with variable sizes of print. It really slowed the process down — and conversely, uniform print sizes made the first 90% of the job almost enjoyable. I averaged one “scan” every 2s.

zokier 2y ago

If you want to get serious on this, get good quality color chart[1] and use that to compare different light sources etc. Just eyeballing resulting colors from random photos and guesstimating the various spectral curves gets you only so far. [1] e.g. https://www.silverfast.com/products-overview-products-company-lasersoft-imaging/it8-targets-for-scanner-calibration-profiling-for-predictable-brilliant-colors/ https://www.silverfast.com/products-overview-products-compan...

dvdkon 2y ago
Yes, but you'd want that colour chart on the type of film you're scanning, for reasons explained in the OP. Sadly all I found in a brief search were calibration targets on slide film, not negatives.
- musictubes 2y ago
  Back in the early 90s I used a Noritsu printer. We had reference negatives on all the different film stocks, or at least all the ones we regularly saw there. We would group the jobs by film type. Set the calibration by the calibration negative and judge exposure and basic color correction by direct viewing of the negative. Another person would check the prints and flag any that needed to be redone for color, dust, exposure, etc. Then we’d change film types. The next time I touched a photofinishing machine in the early 2000s you looked at a screen to make adjustments and we offered digital services like scanning and printing from digital files. I still used my negative reading skills to talk to customers when we were troubleshooting results. Putting the negative on the light table to show them how thin they were or how wildly the color changed when you switched what kind of light the picture was shot in was the quickest way to resolve quality complaints.
- zokier 2y ago
  I'd imagine that just grabbing the reflective target and shooting it yourself on film would get decent results? Assuming the target patches have good spectral coverage

fallinditch 2y ago

I'm planning to do some negative scanning with a phone or iPad as a light source. I know I'll have to make some simple tweaks to the color balance of the scans. I believe it is totally normal to have to make some adjustments to scans, the side by side example in the article seems to show that a white light source is perfectly fine for this work. It's unlikely that an RGB light source would produce scans that don't require any adjustments, so I'm failing to see the benefit.

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cedricd 2y ago
I've scanned a few hundred images using an iPad as the light source. I've tried both a white screen and a bluish screen designed to basically invert the orange cast from the negative. Both seem to work well. The bluish thing works quite well, but it turns out that different rolls need slightly different light color to compensate, so it wasn't worth the trouble. In the end the best result was buying a license for Negative Lab Pro[0] to post process everything [0]: https://www.negativelabpro.com/ https://www.negativelabpro.com/
- fallinditch 2y ago
  That's a good recommendation, thank you. It's amazing how complicated film photography has become in the digital era! My next task is to ditch Lightroom/Photoshop subscription. I'm going to give Darktable a go. Edit: aaah, I see NegativeLabPro needs Lightroom, hurrumph...
- kosma 2y ago
  Seconded. NLP is well worth the money - not just in results, quality, and time saved, but also in finding joy in shooting and scanning color.
- tsaiDavid 2y ago
  I held out for sometime myself, but NLP is excellent. It works particularly well with an old Pakon I still use as well as using a camera to “scan”.

zackmorris 2y ago

Even after working with colorspaces for decades in Photoshop and various game dev tools, I find color conversion mystifying. I've studied all of the equations and given it my best effort, but would not bet real money that the colors I'm displaying are close to real life. It's like the game of telephone, I just can't trust so many steps. So for this article, I don't see mathematical proof that the negatives have been inverted accurately, regardless of method, even though I'm sure the results are great. I suspect it comes down to subjective impression. Here's a video I found discussing monitor calibration: https://www.youtube.com/watch?v=Qxt2HUz3Sv4 https://www.youtube.com/watch?v=Qxt2HUz3Sv4 If I could fix everything, I'd make all image processing something like 64 bit linear RGB and keep the colorspace internal to the storage format and display, like a black box and not relevant to the user. So for example, no more HDR, and we'd always work with RGB in iOS instead of sRGB. Loosely that would look like: each step of image processing would know the colorspace, so it would alert you if you multiplied sRGB twice, taking the onus off of the user and making it impossible to mess up. This would be like including the character encoding with each string. This sanity check should be included in video card drivers and game dev libraries. If linear processing isn't accurate enough for this because our eyes are logarithmic, then something has gone terribly wrong. Perhaps 16 bit floating point 3 channel RGB should be standard. I suspect that objections to linearity get into audiophile territory so aren't objective. For scanning color negatives, the brand of film would be mapped to a colorspace, the light source would have its own colorspace, the two would get multiplied together somehow, and the result would be stored in linear RGB. Inversion would be linear. Then the output linear RGB would get mapped to the display's sRGB or whatever. My confusion is probably user error on my part, so if someone has a link for best practices around this stuff, I'd love to see it.

lcrs 2y ago
Colour in the Photoshop/gamedev world is often handled pretty casually, but if you're interested the moving picture world gets a lot more rigorous about it and there's tons of documentation around the ACES system in particular: https://github.com/colour-science/colour-science-precis https://github.com/colour-science/colour-science-precis https://acescentral.com/knowledge-base-2/ https://acescentral.com/knowledge-base-2/ As you suggest storage in linear 16-bit float is standard, the procedure for calibrating cameras to produce the SMPTE-specified colourspace is standard, the output transforms for various display types are standards, files have metadata to avoid double-transforming etc etc. It is complex but gives you a lot more confidence than idly wondering how the RGB triplets in a given JPG relate to the light that actually entered the camera in the first place...

keepamovin 2y ago

This is cool. The original looks kinda green to me. Awesome.

alnwlsn 2y ago

Anyone know if this is the right technique to use on 8/16 mm movie film (which is a positive instead of negative)? Modifying an old projector to go one frame at a time is the easy part, but you can't use the original halogen bulb since it will burn a hole right through the film at that speed.

Finnucane 2y ago
Yeah, it would be interesting if this makes much of difference for slide film, either e-6 or Kodachrome (I am old and have both).
- tecleandor 2y ago
  In the article they say that for positive film (slides, at least) white light is generally better than rgb, but it would be nice to test it.
  - Finnucane 2y ago
    Missed that. I guess that makes sense, since those films are designed for projecting more than printing.
smogcutter 2y ago
There are also rotoscoping and analysis projectors designed to hold on a frame.
qingcharles 2y ago
I scanned a lot of positives on an Epson V850 flatbed just fine. Except for the resolution and the setup being a bit finicky, there wasn't much between that and the $25K X5 scanner I had.

felixhandte 2y ago

Awesome work! I get exactly that green cast and muted color range off of my flatbed scans (Epson v800). This is a really intriguing path to fixing them I hadn't considered. It seems like the writeup here doesn't specify what you're using for the actual imaging? A flatbed scanner? A camera?

esafak 2y ago

After all that work I was expecting a chromaticity diagram to demonstrate the expanded gamut, but nice job regardless.

flimsypremise 2y ago
RGB scanning doesn't actually expand the color gamut, but removes erroneous color information. If you use white light you end up recording color information from the dyes in wavelengths outside of those that RA-4 paper is sensitive to, and which the color engineers who designed the film never intended it to be used with.
- esafak 2y ago
  Thank you for the correction. Then you can measure the color difference?
  - flimsypremise 2y ago
    Yes, there's actually a very good test for a properly inverted color negative. You need a negative of a greyscale step scale from light to dark. If the color channels are properly linear relative to one another in the scanned image, you should be able to white balance any one of the patches and have all of the others remain neutral: by which I mean each patch should have equal amounts of red blue and green. In practice the characteristic curves of film often mean the darkest and lightest patches are often slightly more green or red, but its very close. So the process would be, using the RAW scan of the image (the orange mask intact): 1) Invert the image. 2) White balance on any patch. 3) Sample the color balance of every other patch. They should have equal amounts of all colors.
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assimpleaspossi 2y ago

Looking at the results, it looks to me that the print with the white light has far more detail while the RGB print has washed out ground under the tower.

pimlottc 2y ago
Yeah, it's not clear to me either that the RGB image is obviously better, especially without knowing that actual conditions were like when the photo was taken. Perhaps the author could explain why they find one image superior instead of just putting two images side-by-side, with the implied message that "any idiot can see that <x> is better".

throw0101b 2y ago

> White light scan captured using 95+ CRI 5000K light source. RGB scan captured using custom 450nm+525nm+665nm light source. While high-CRI is better than low(er)-CRI, one criticism is that the 'score' is somewhat lacking in it measure an important component: > Ra is the average value of R1–R8; other values from R9 to R15 are not used in the calculation of Ra, including R9 "saturated red", R13 "skin color (light)", and R15 "skin color (medium)", which are all difficult colors to faithfully reproduce. R9 is a vital index in high-CRI lighting, as many applications require red lights, such as film and video lighting, medical lighting, art lighting, etc. However, in the general CRI (Ra) calculation R9 is not included. […] > R9 value, TCS 09, or in other words, the red color is the key color for many lighting applications, such as film and video lighting, textile printing, image printing, skin tone, medical lighting, and so on. Besides, many other objects which are not in red color, but actually consists of different colors including red color. For instance, the skin tone is impacted by the blood under the skin, which means that the skin tone also includes red color, although it looks much like close to white or light yellow. So, if the R9 value is not good enough, the skin tone under this light will be more paleness or even greenish in your eyes or cameras.[25] * https://en.wikipedia.org/wiki/Color_rendering_index#Special_value:_R9 https://en.wikipedia.org/wiki/Color_rendering_index#Special_...

twic 2y ago

The thing i found most interesting here is the brightness enhancing film: https://newhavendisplay.com/blog/brightness-enhancement-film-bef/ https://newhavendisplay.com/blog/brightness-enhancement-film... Basically, it's a collimator: it takes light going in all directions (eg from a lamp), and turns it into light all going in one direction. What does it look like to look through? Do objects appear brighter? I suppose they appear brighter but also smeared out?

grvbck 2y ago
> What does it look like to look through? Do objects appear brighter? I suppose they appear brighter but also smeared out? Pretty much exactly so: https://youtu.be/ugkjNPH1J-4 https://youtu.be/ugkjNPH1J-4

flimsypremise 2y ago

So I wrote an article about this a few years back and also developed a custom RGB light for my own scanning: https://medium.com/@alexi.maschas/color-negative-film-color-spaces-786e1d9903a4 https://medium.com/@alexi.maschas/color-negative-film-color-... There's also some proper academic research into this subject going on currently: https://www.researchgate.net/publication/352553983_A_multispectral_design_for_a_new_generation_of_film_scanners https://www.researchgate.net/publication/352553983_A_multisp... One thing that's important to note about this process is that the idea is not to _image_ the film, but rather to measure the density of each film layer and reconstruct the color image from that information. This is a critical realization, because one of the most important things to know about color negative film is that the "color" information in the negative actually only exists relative to the RA-4 printing system. Negatives themselves don't have an inherent color space. Cool to see someone else working on this though. I actually considered those drivers for my build, but I ended up building a very high frequency, high resolution PWM (30khz/10bit) dimming solution with TI LM3409 drivers. It's very hard to get uniform light as well so I ended up getting some custom single chip RGB LEDs. https://i.imgur.com/BVM9p6Q.jpeg https://i.imgur.com/BVM9p6Q.jpeg https://i.imgur.com/5oozHnN.jpeg https://i.imgur.com/5oozHnN.jpeg I've been working on this for a few years, and what I will say is that there's actually another level of complexity beyond just implementing the light. There's a lot of testing to ensure that you're getting proper linearization of each channel, and there's still a color crosstalk problem arising from the misalignment between the color sensitivity of most modern digital cameras and the bands that are used to scan color negatives. It requires some additional tweaking to get all of the color information in the correct channel. You can also very easily end up saturating a channel without realizing it as well. Oversaturated reds are a common occurrence in RGB scanning. I'd also note that the wavelengths you should shoot for are more along the lines of 440nm 535nm 660nm, which correspond to the Status M densitometry standard. This standard was designed specifically for color negative film.

m463 2y ago
Is there a way to process dust/scratches? Like wavelengths outside the chosen r/g/b range?
- 2y ago

hoherd 2y ago

Maybe it's because I'm colorblind, but the top-right image looks much better than the bottom-right image to me. Can somebody explain why the bottom-right image is allegedly superior? I know there's a write up about what's going on and all the science behind it, but what I'm asking about is what you as a person with color receptive vision sees that is better.

realreality 2y ago
The top photo has a blue-green cast, whereas the bottom photo has a magenta cast. Maybe the bottom one is a more realistic reproduction of the scene, but I also prefer the top one, which is more saturated and closer to what I associate as a film image. Each kind of film has its own character and color variations; it’s silly to try to neutralize everything.
asimpletune 2y ago
I looked at both before knowing which was which. Immediately I recognized the look of the top right photo, whereas the bottom right didn't quite seem to have "the look". So, I think it might be that it looks better to you because it looks more like how a photo looks. It's similar to how younger people may prefer 60fps or weird settings on TV shows that give it the "soap opera effect" vs how older people can't stand them. After switching back and fourth and really looking closely at each one I ended up deciding that I liked the bottom right photo, even though I could recognize the top right one had a more classic film look. For me it was just because there was more detail in the colors. The original scan was kind of washed out in the blues I guess, as well as being a little more red in the dirt area.
- ralferoo 2y ago
  I too preferred the top right photo. Arguably, it has less detail in the tree line, the city is neither better or worse, just different, but for me the skyline and sky are far superior with the top right photo. Maybe this is prejudiced because this is how I remember old photos to be... But then, isn't that the point of scanning old negatives anyway - to recreate what the old images on them would have looked like at the time? Arguably though, the correct solution is to preserve the source information as much as possible, so similar to what it proposed - scan the images using light sources that correspond to the peaks of the chemicals used in the negative, and then colour grade directly from that using a modified inverted curve. Doing it that way should permit both outputs by changing the curves used in colour grading, and I suspect the real issue is just "inverting colours" isn't the most appealing visually, just as most professional photos are colour graded to some extent because the raw images don't look as appealing.

anfractuosity 2y ago

Interestingly that doesn't appear to mention infrared from a quick scan, which is used to help remove dust as far as I understand. (I've got an old Canon FS4000, which uses IR)

m463 2y ago
I scanned negatives long ago without IR and it was horrible. Dust and fiber were a major headache, especially when scanning lots of film. But since we're living in the future, I suspect we could make AI models that would work practical magic.
- anfractuosity 2y ago
  Heh, yeah good point, I imagine that would work well too, didn't think of that.
- eloisius 2y ago
  If AI was in the mix, regenerating my images, personally I wouldn’t bother with scanning, and I’d just go back to digital.
  - m463 2y ago
    All the scanned photos I've worked with were taken pre-digital.

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zokier 2y ago

Btw regarding the camera sensitivity, if you shoot raw and just shoot the different colors separately, you can mostly ignore the spectral characteristics of the sensor. Debayering might end up being very different than standard though.

mikewebkist 2y ago

It seems like an alternative would be a broad-spectrum white light source with narrow-band color filters that correspond to similar wavelengths to the LEDs mentioned. That would require simpler light source but more costly subtractive filtering. All those old-school minilabs pre-blue LEDs...they must have used white light sources and filters, right?

xkcd-sucks 2y ago
Being able to tune the intensity ratio of the bands, especially with source age, is nice so that everything's in the middle of the sensor's dynamic range ... optical filters can be pretty cheap at scale or as surplus, but, well behaved broadband light sources aren't so easy to find.
jackw01 2y ago
Author here, I was curious about this too since I would have expected most film scanners from the 90s-2000s to use incandescent light sources if high-CRI light was really the way to go. Minilabs that made direct optical prints to RA-4 paper did use white light sources with filters, since RA-4 paper is already only sensitive to narrow bands of light. In the mid-90s, Fujifilm and others introduced minilabs that could also scan film and produce prints from digital files. These all used RGB LEDs to scan the film, and they must have had a very good reason to since blue LEDs were barely ready for commercial use at the time.

strogonoff 2y ago

TL;DR Negative film is (obviously) intended not for viewing by humans, but for a specialized development process. Digital cameras are geared towards capturing images as humans would perceive them, and in regular photography using full spectrum light supposedly makes metameric failure less likely. Thus, it may appear counter-intuitive to a seasoned photographer that using a specific narrow band RGB lighting can be preferable when digitizing typical negative film, working around the use case mismatch and improving colour reproduction.

Animats 2y ago

Why not use a single monochrome sensor and just turn on R, G, and B lights for three images? Many flatbed scanners do that.

mplewis 2y ago
This saves a lot of time in post-processing.

coisasdavida 2y ago

Anyone knows a similar supplier in Europe I could source the parts from?

bijutoha 2y ago

The idea of using narrowband RGB light sources for scanning color negatives is fascinating. It’s great to see a practical approach that addresses the common issues with white light scans. I’m curious: have you tested this setup with different film stocks, and if so, how consistent were the results across various brands?