Figure 3.11.3 from Stockman, A., & Brainard, D. H. (2009). Color vision mechanisms. In M. Bass, C. DeCusatis, J. Enoch, V. Lakshminarayanan, G. Li, C. Macdonald, V. Mahajan & E. van Stryland (Eds.), The Optical Society of America Handbook of Optics, 3rd edition, Volume III: Vision and Vision Optics. New York: McGraw Hill.
Model of the early postreceptoral stages of the visual system. The signals from the three cone types, S, M and L, are combined to produce an achromatic or luminance channel, L+M, and two cone-opponent channels, L-M and S-(L+M). Note that there is assumed to be no S-cone input to the luminance channel. Based on Figure 7.3 from Boynton’s book (Boynton, 1979).
Boynton, R. M. (1979). Human Color Vision. New York: Holt, Rinehart and Winston.