Grayscale Working Spaces in Photoshop

Grayscale working spaces have to do with two parameters — viewing and dot gain of grayscale images (Image➪Mode➪Grayscale). You can choose Gray Gamma 1.8 for a Macintosh monitor or Gray Gamma 2.2 for a PC monitor. You can also view an image according to how it will print, based on typical dot gain.

Dot gain is how much ink the paper absorbs, thereby increasing the size of every halftone dot.
When continuous-tone images are digitized, they are converted into a series of dots known as a halftone.

If you’re preparing graphics for the Web, you may want to set your working space to Gray Gamma 2.2 — whether or not you’re using a Mac — because most of the Web surfers worldwide are PC users.

For print work, leave the setting at Dot Gain 20% unless your commercial printer tells you otherwise.
Don’t forget — you still have to adjust another working space.