Copunctal Points

A copunctal point is where color confusion lines intersect for a certain dichromat.  It corresponds to the missing cone primary. The red, green and blue dots are the copunctal points of protanope (missing long wavelength cone), deuteranope (missing middle wavelength cone) and tritanope (missing short wavelength cone) respectively.

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Here the copunctal points derived by Smith and Pokorny (1975) are used because they are probably the only set of copunctal points for 1931 CIE color matching functions.   Please see Stockman, A., Sharpe, L.T. (1999) for a thorough review of cone primaries. Colblindor has a very readable blog explaining copunctal points and confusion lines.