Creating Saturation Channel / Mask

Question

Hello.
I'm interested in making a Saturation Mask. Actually I want to extract the Saturation Channel.
I know there's HSL / HSB Plug-In made by Adobe which is able to do so.
Yet, I'm interested if there's an option creating it using the Blend Modes (Just like adding a Solid Black Layer in Color Mode creates a Luminosity Mask).
Could anyone assist?
Thanks.

Answer 1

This thread has revealed that not all methods out there which allegedly produce a SATURATION mask are valid.
That seems true for LUMINOSITY masks as well, and I'd like to adress that.
In the same way that a saturation mask was defined, let's define a luminosity mask as having gray values which everywhere correspond to the underlying luminosity. Since the  0-255 luminosity range is the same as the gray value range, correspondence in this case is equality (the 2.55 saturation multiplier is not needed).
Luminosity in PS is  0.3R + 0.59G + 0.11B. Just for example, masking a pure, fully bright red (255/0/0) would give a gray value of 0.3 x 255 = 76. Likewise masking a pure, fully bright green (0/255/0) gives 150, and pure, fully bright blue (0/0/255) gives 28.
The method for creating a luminosity mask cited by Royi Avital in his original post (overlaying a black layer in color blend mode) is valid in that it meets the foregoing definition of a luminosity mask and, in fact, can be expanded to overlaying any shade of gray from black to white in any of three blend modes, specifically hue, saturation, or color blend modes (note that the luminosity mode is excluded).
There is another commonly-advocated method for producing a luminosity mask: ALT-CTRL + tilde (~). For the life of me, I cannot get it to produce grays that equal the luminosity. Since this seems to be the widely-adopted method, any challenge must indeed be hesitant. Can somebody out there substantiate or disprove my result. Why doesn't this accepted method conform to a reasonable definition of a luminosity mask?