Question Regarding Slide Film

[yunhao-jiang]

I'm exploring using RGB light source to scan films and does found that it will produce very saturated result. It can be pretty though, but I do question the color accuracy.

My main question lies in the spectral sensitivity curves and the RGB light source. From the chart below (Fujifilm Provia 100F's datasheet), it seems that slides are also very similar to color negative where the three layers are designed to respond to specific wavelengths. Then why not using RGB light source the best way to reproduce such color?

I understand that the slides are probably "designed" to be projected with a "normal" white light (continuous on the spectrum, such as sun light, projector light), but I'm wondering maybe the "original" color of the slides are different?

Thanks!

[harrypm]

What I'm also wondering with fresh current film stocks (or just ones we use mainly) is it worth making some neutral reference frames with a colour checker 48 square chart, kinda like how we typically use an IT8 target transparency for scanner profile calibration.

[yunhao-jiang]

What I'm also wondering with fresh current film stocks (or just ones we use mainly) is it worth making some neutral reference frames with a colour checker 48 square chart, kinda like how we typically use an IT8 target transparency for scanner profile calibration.

@harrypm I believe yes, and I think someone did similar work already here.

For IT8 targets, you can use Lumariver Profile Designer to generate a customized DNP profile (kinda like how icc profile works with scanners, DNP profile tells Lightroom how to interpret RAW images). The software itself is not cheap though, to use customized target you will have to get the 250 Euro Repro version.

One thing I'm not sure is that, when we use IT8 targets to calibrate the color, it seems a bit controversial to the RGB process. I'm no professional here so, not exactly sure what's the best way of doing so.

[Jiyone]

Yes slide film should be digitized and a profile (from an IT8 or other) should then be applied on it.
Slide film is made to be seen directly so an RGB light source shouldn't be needed, but if you are experiencing color shift, having each dye layer recorder on each RGB channel can be helpful for color correction before applying the profile.