It is in spanish language. Can it help you? I created 3 channels for hightlights, 3 for shadows and 3 for midletones.
https://youtu.be/y1mRb0P1LHY
The steps are those indicated by Smadell:
Duplicate background 2 times.Name the 1st duplicate “Light Temp”Name the 2nd duplicate “Dark Temp”With “Dark temp” layer selected, choose Layer > InvertSelect layer “Light Temp”In Layers panel, Command-Shift-Click on layer icon to create luminosity selectionIn Channels panel, right click on Pixel Selection and choose Create Spare Channel.Rename this channel Lights 1Deselect the selection.In Channels panel, right click on Lights 1 and choose Load to Light Temp alphaIn Layers panel, Command-Shift-Click on layer icon to create luminosity selectionIn Channels panel, right click on Pixel Selection and choose Create Spare Channel.Rename this channel Lights 2Deselect the selection.In Channels panel, right click on Lights 2 and choose Load to Light Temp alphaIn Layers panel, Command-Shift-Click on layer icon to create luminosity selectionIn Channels panel, right click on Pixel Selection and choose Create Spare Channel.Rename this channel Lights 3Deselect the selection.Delete layer “Light Temp”Select layer “Dark Temp” [remember - this is the inverted version of the background layer]In Layers panel, Command-Shift-Click on layer icon to create luminosity selectionIn Channels panel, right click on Pixel Selection and choose Create Spare Channel.Rename this channel Darks 1Deselect the selection.In Channels panel, right click on Darks 1 and choose Load to Dark Temp alphaIn Layers panel, Command-Shift-Click on layer icon to create luminosity selectionIn Channels panel, right click on Pixel Selection and choose Create Spare Channel.Rename this channel Darks 2Deselect the selection.In Channels panel, right click on Darks 2 and choose Load to Dark Temp alphaIn Layers panel, Command-Shift-Click on layer icon to create luminosity selectionIn Channels panel, right click on Pixel Selection and choose Create Spare Channel.Rename this channel Darks 3Deselect the selection.Delete layer “Dark Temp”In Channels panel, right click on Lights 1 and choose Load to Pixel SelectionIn Channels panel, right click on Darks 1 and choose Intersect with Pixel SelectionIn Channels panel, right click on Pixel Selection and choose Create Spare ChannelRename this channel Midtones 1Deselect the selection.In Channels panel, right click on Lights 2 and choose Load to Pixel SelectionIn Channels panel, right click on Darks 2 and choose Intersect with Pixel SelectionIn Channels panel, right click on Pixel Selection and choose Create Spare ChannelRename this channel Midtones 2Deselect the selection.In Channels panel, right click on Lights 3 and choose Load to Pixel SelectionIn Channels panel, right click on Darks 3 and choose Intersect with Pixel SelectionIn Channels panel, right click on Pixel Selection and choose Create Spare ChannelRename this channel Midtones 3Deselect the selection.