Action: RGB>Lab L channel
		Duplicate first document
			Name:  “RGB to Lab L channel”
		Select Background
		Set Selection
			To: all
		Copy
		Set Selection
			To: none
		Convert Mode
			To: Lab color mode
			With Flatten
		Paste
			Anti-alias: none
		Set current layer
			To: layer
			Name:  “RGB L +old colour”
		Select lightness channel
		Show a channel, b channel
		Apply Image
			With: calculation
			Source: lightness channel of Background
			With Preserve Transparency