Just thought I would share this with you if you are trying to peg down a quick, easy and powerful mono conversion routine. And I have tried them all, "Channel Mixer", "Black and White", the Fred Miranda Conversion routine, etc, etc, etc and I kept having a tough time balancing speed, power, and simplicity.
The method I came up with allows you to emulate an infinite set of filters with just one slider - so you can easily pick out what suits the shot best.
You can create an Action, but it is so fast, that it take almost as much time to run the action as it is to do it step by step.
1) Duplicate the Layer (Background Copy)
2) "Desaturate" the Background Copy layer and set the blend mode to Color.
3) Go to the Background (Bottom) layer and select "Image - Adjustments - Hue/Saturation" from the drop down menu.
4) Slide the "Hue" slider back and forth and notice how that affects the relative densities in the shot!
The cool part is this works in older versions of PS or Elements that don't have the "Black and White" choice for Mono Conversion! Probably works with GIMP, too! (Someone want to try it and see?)
I find that this works perfectly well for 99% of my mono conversions.
Give it a try and see if it works for you too.