[flimsypremise]

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-...

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.

[Intralexical]

> 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.

Do each waveband separately?

[m463]

Is there a way to process dust/scratches? Like wavelengths outside the chosen r/g/b range?

[matthews2]

Dust (and scratches?) can be detected with an infrared scan. The IR scan is only used to detect defects, and then something like a spot removal tool is automatically applied to the defect areas.

https://www.hamrick.com/blog/digital-ice.html

[flimsypremise]

Technically, yes. I know a few people have done it. In a practical sense it is very difficult and you are unlikely to get it working without a lot of trial and error. The tricky part is that the IR image needs to be perfectly aligned with the rest of the image data, which introduces a number of difficulties.

• You can modify a sensor for IR, though this is often a costly and difficult modification. But even if you do so, the IR focal distance is different from the visible light focal distance. So for every shot you need to refocus for IR, but also ensure that the refocussed IR image is exactly the same size as the visible image.

• You can use another sensor that is sensitive to IR, but its probably not going to have the same resolution, you're going to struggle to somehow have both cameras see the target image, and then once you get both exposures, alignment becomes a problem.

So yeah, doable but non-trivial.