Digitizing color slides with camera: backlight temperature and chromatic adaptation

[River Mantis]

I have an established workflow for black and white negatives but I have never worked with color slides before. So here are my thoughts. Ektachrome E100 is a daylight balanced film. When applied to a transparency it means, I guess, that the white card shot under daylight will have the color of the projector's light source when the slide is projected. At the same time slide is meant to be viewed in a dark room with no other light sources. So viewer's chromatic adaptation should theoretically mask any possible difference in sources' temperature. From this perspective the obvious choice would be to adapt the digitized image from the backlight to a standard whitepoint of the final space. In other words the white balance must be set by backlight as a reference. But this formally correct approach leads to a way too neutral and kind of flat result on a screen while when I see the slide over my CS-Lite backlight in its warm (aka "slide") mode the colors are so much more vibrant. So what's the right way of digitizing color slides?

 

[Chan Tran]

That was the right way. If you want your slide to look different then process a bit in post.

 

[MattKing]

Slide films were designed to be projected using tungsten (which includes halogen) bulbs.
Most importantly, try to use a backlight with a continuous spectrum.
Be cautious about using LED sources and relying on a quoted a "Colour Rendering Index" or "CRI". That CRI measurement standard is aimed at different criteria than those that may make a difference with digitization.