Please explain this color blending mode formula so I can replicate it in PHP/ImageMagick

Question

I\'ve been trying to use ImageMagick to replicate Photoshops Colour Blend Mode. I found the following formulas in an online guide but I don\'t know what they mean. Do I just

Answer 1

A is the Foreground pixel, B is the Background pixel, C is the new pixel. H is the Hue value for each pixel, S is the Saturation value, L is the Luminance value, and Y is the Brightness value. (Not sure what the difference is between luminance and brightness though.

Anyway, in the first example the Hue(H) and Saturation(S) values of the new pixel(C) are copied from the Foreground pixel(A) while the Brightness(Y) value of the new pixel is taken from the Luminance(L) value of the Background(B) pixel.