If we don’t have a luminance image, we need to do a channel extraction immediately after we do channel integration. We wait until we integrate our channels before we start to create a synthetic luminance channel because we want to use details from every filter in our synthetic luminance.
The channel extraction process looks just like the channel combination process, except this time we use the CIE L*a*b color space and select the L channel.
Once complete, you have a luminance image.
Set the image identifier as LUM and save for processing later in our workflow.
With the luminance channel extracted, we can now continue with calibrating our colors to better balance the red, green and blue channels.