Ever had an image open in photoshop with semi-transparent pixels and you needed to know the alpha value of those semi-transparent pixels? Turns out photoshop can do it, it’s just hidden by default. To enable this feature, open the Info window, choose Panel Options and then set the Second Color Readout mode to Opacity. Now when you use the color dropper tool and mouse over a semi-transparent pixel it will show you the opacity as a percentage as well as the color.

Solution found here, duplicated here for link rot protection.