The Calculations command is an old school way to work with channels and color (it’s been around since before Photoshop had layers. It’s also a great way to combine complex color channel data to build an alpha channel. This can then be converted into a layer masks for a nondestructive way to hide pixels in a photo.
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Disclaimer: This is just one way to work with masks.
Rich has published over 100 courses on Lynda.com. Rich has authored several books including From Still to Motion, Understanding Photoshop, Professional Web Video, and Creating DSLR Video.