Can color filters really be faithfully recreated digitally? Challenge inside.

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polyrhythm New Member • Posts: 1
Can color filters really be faithfully recreated digitally? Challenge inside.

There's been this seemingly-uncontested idea I've read that one can simply do away with colored lens filters and do the equivalent in post with RGB channel mixing or channel-independent RGB curves.

While I think that one can get close, especially in typical conditions, I think people underestimate the huge amount of assumptions being made when you're trying to recreate a spectral phenomenon[1] with simple RGB approximations.

I came up with a little experiment to show the difficulty of this.

I have a color chart that I've shot with and without a yellow filter under neutral (~5500k) lighting, and then again under a very blue saturated light. The challenge is to come up with a channel mix/curve/whatever preset that faithfully recreates the "filtered" scenes digitally. I can't do it, but maybe you can. I didn't bother with white balance or anything, feel free to make any adjustments you like prior to embarking on "the challenge."

Neutral light with no filter

Neutral light with yellow filter

More difficult case:

Blue light with no filter

Blue light with yellow filter

Obviously, the blue light scenario is going to be significantly more difficult to recreate using simple RGB mixers, but I'm curious if anybody can figure it out.

Download RAW files here

Lastly, you might ask yourself if this matters. I guess for most cases it doesn't. I like shooting black and white where extreme color filters used to be quite common, and now this has switched to digital post, but I feel a bit guilty not using my color filters if it turns out I can get results with them I can't get digitally.

1. Recall that light is made up of wavelengths, of which the visible spectrum is a fairly narrow portion. A physical filter will have a very specific response to certain wavelengths which can only loosely be approximated by dialing down an RGB channel - which is itself a simplification of the idea of light to work with our lizard brains interpreting those wavelengths.

Tech specs:

Shot in RAW with a Sony RX100, the lens filter is a Marumi MC-Y2.

Sony RX100
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