A Better Light Source for Scanning Color Negative Film
Narrowband RGB light sources enhance color negative film scanning quality by minimizing signal overlap, while ideal wavelengths are >650nm for red, 520-550nm for green, and <450nm for blue.
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Narrowband trichromatic (RGB) light sources are more effective than broadband (white) light for scanning color negative film, as evidenced by the superior quality of images produced with RGB. This is due to the way color negative (C-41) film interacts with light; it uses cyan, magenta, and yellow dyes that absorb specific wavelengths. White light, which covers a broad spectrum, can lead to overlapping signals that complicate the recovery of individual dye layers, resulting in lower quality scans. In contrast, RGB light sources minimize this overlap, allowing for straightforward color inversion and adjustments without the need for specialized software. The ideal RGB wavelengths for scanning are >650nm for red, 520-550nm for green, and <450nm for blue, though commercially available options may not meet these specifications. Users can create their own RGB light source using specific LED types and a diffuser for even illumination. The article also discusses the scanning workflow, emphasizing the importance of fixed white balance and exposure settings. Overall, using RGB light sources significantly enhances the scanning process for color negative films.
- RGB light sources provide better quality scans of color negative film than white light.
- Scanning with white light can lead to overlapping signals and lower quality images.
- Ideal RGB wavelengths for scanning are >650nm (red), 520-550nm (green), and <450nm (blue).
- Users can build custom RGB light sources for optimal results.
- A proper scanning workflow is essential for achieving high-quality images.
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- Many commenters express skepticism about the necessity of narrowband RGB lighting, suggesting that adjustments in post-processing can achieve similar results.
- Several users share personal experiences with scanning techniques and equipment, highlighting the importance of consistent color developing services.
- There is a discussion about the complexities of color accuracy and the challenges of achieving true color representation in digital formats.
- Some commenters propose alternative methods, such as using broad-spectrum light with filters or monochrome sensors, to improve scanning quality.
- Concerns are raised about the impact of film processing and chemistry on the final scan quality, emphasizing the need for reliable developing practices.
26 commentsMy 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.
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?
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
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.
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_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/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.
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_...
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?
[1] e.g. https://www.silverfast.com/products-overview-products-compan...
All those old-school minilabs pre-blue LEDs...they must have used white light sources and filters, right?
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?
I think I still have an spectrophotometer around to check that...
(I've got an old Canon FS4000, which uses IR)
maybe close enough is fine for this, though
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