Extract Luminosity

This recipe will create a layer containing the luminosity of the image, which is similar to using the luminosity channel in Photoshop 6. This could be used to convert an RGB image to monochrome or to adjust the levels without shifting the color.  To do this change the layer blend mode to Luminosity and then adjust the layer levels.  The result is similar to the Auto Contrast adjustment.

Follow the steps carefully, there are several intermediate layers created and it is important to be on the right layer for each step.

You only need to do Step 2 or Steps 3&4, not both.

Once you are comfortable with the results, the Effect is much easier and faster.