- Photoshop > Menu > image >
- Calculations uses two Channels to make a more refined selection, which can be output as a new Channel or a selection.
- Source 1 layer can be imagined as actually being on top of the Source 2 layer.
- Opacity determined the opacity of the top layer, so by setting it to zero the bottom layer is revealed.
- Blending modes Add and Subtract are only available in Calculations, and the Offset and Scale are only visible when these options are selected.
- Offset goes from -255 to +255 and is the amount of lightening or darkening applied to the result.
- Scale can be between 1 and 2.
- Clicking on Mask reveals the panel below it.