Confused about HSI and HSL color spaces

Question

I am reading a book for image processing algorithms and for the contrast algorithm it says that I can either go RGB->HSL or RGB->HSI first and than apply a contrast technique for grayscale images, on the lightness component.

Then it gives this formula only, not other formulas for color conversion:

L(x,y) = 0.299*R(x,y) + 0.587*G(x,y) + 0.114*B(x,y)

This formula is neither for the L in HSL, neither for the I in HSI and that is what confuses me.

Thanks

Answer 1

It's the luma value mentioned in the fourth bullet here: http://en.wikipedia.org/wiki/HSL_and_HSV#Lightness