Now press Ctrl+Shift+Alt+E/Cmd+Opt+Shift+E. Open your layer panel and you’ll see a new layer is created. Now go to Window>Channel. Click on red channel. Now we need to copy the red channel. Press Ctrl+A/Cmd+A to select the whole image.
Now create a new layer by pressing Ctrl+Shift+N/Cmd+Shift+N. Rename the layer to “red channel”. Now press Ctrl+V/Cmd+V to paste it. Now hold down Ctrl/Cmd and then click on layer thumbnail of the red channel. This will select the red channel present in an image.
Now go to Layer>Layer Mask>Reveal Selection. Your image should look like this.