Real quick. I was going through today's image and know I wanted to pop up the reds. A fair amount in the structure and a goodly amount in the flag. I knew it would require a mask, so I went to the Channels Panel to find which (duh!) Channel had the most contrast. It was the usual suspect of the Blue Channel. Highlighted the Blue Channel and went immediately to Calculations (Image/Calculations). I tagged the Blend Modes dropdown and cycled through (down arrow key) the choices looking for the maximum contrast. Ideally, pure black and pure white. As I was tapping through I saw one of the modes gave a very dramatic rendition of the clouds. Lots of shades of grey all over the place. I quickly saved that as a new Alpha Channel. (All Masks are Alpha Channels, even in Adobe Photoshop Elements.) I then went back to finish my original goal of finding a solid black and white Mask of the structure and flag. I found one Blend mode (probably Hard Light or something similar) that dropped out the sky almost completely. I used levels to take the sky up to about 90% white. Then I used a tool that I dislike almost as much as I dislike the Eraser Tool (not even going to post the shortcut keystroke for that foul tool). I used the Tragic (Magic) Wand Tool (W) to select the sky area. The tool was set to Continuous being turned off. It picked up the 90% of the white and I was able to add (Shift) to get the small amount left. I then Inverted the Selection (Ctrl/Shift/I [eye]) giving me everything that wasn't sky. A quick Fill with Black completed the Mask. The finishing steps are outlined after the "read more".