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Comment by ekunazanu | Hacker News Reader

> Because there’s a lot of overlap between the red and green cones, our brain subtracts some green from red, yielding this spectral response:

No, cones do not produce a negative response. The graph shows the intensity of the primaries required to recreate the spectral colour at that wavelength. The negative implies that the primary was added to the spectral colour to match it with itself, instead of adding it with the other primaries.

https://en.wikipedia.org/wiki/CIE_1931_color_space#Color_mat...

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> No, cones do not produce a negative response.

Yes, they do, after the photoreceptors. Those CIE colorspace curves aren't biology, and shouldn't be interpreted as such.

LMS colorspace is the (currently understood) biological colorspace [1], and contains inhibitions, from the opponent process [2] found in the meatware [3]:

red-green: L - M

blue-yellow: S - (L + M)

This contains a nice introduction to biological colorspace [4].

[1] https://en.wikipedia.org/wiki/LMS_color_space

[2] https://en.wikipedia.org/wiki/Opponent_process

[3] https://en.wikipedia.org/wiki/Lateral_geniculate_nucleus#Col...

[4] https://color2.psych.upenn.edu/brainard/papers/Stockman_Brai...

Oh I was referring to the response of the cones itself (not the response after the opponent process). I was under the assumption there's no measured curves for the responses after having gone through the opponent process in the neuron-layer(?), so the graph and caption were conflating the response of the cones with color matching functions.

> This contains a nice introduction to biological colorspace

Looks like an interesting read, thanks for sharing!

> No, cones do not produce a negative response.

not what was claimed at all...

>> yielding this spectral response: [graph with negative values]

That's what I gathered from spectral response. Usually spectral response in this context refers to the responsivity of the cones. Even when accounting for 'brain subtracting green from red' (which I assume comes from the opponent process theory) the following graph has nothing to do with it. The captions too read 'Yes, this results in red having negative sensitivity @500 nm', implying the red (L) cones have a negative sensitivity to cyans — which, again, is not really the case.

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