|Desaturated and Fade Adjusted|
So, why not make life easier and convert the image to grayscale with a simple click in Photoshop? This is what I used to do and found it much easier to see the values, however, details were lost and the contrast was slightly altered. I thought it was just a compromise I had to make. Then I stumbled upon the Desaturate button :) I really should play with my software more as I am sure it can do a zillion things to make my life easier!
So by using Desaturate and Fade photos are converted to black and white without loosing any of the details and keeping the bright highlights and deep rich darks. Instructions are below for Photoshop but I would imaging other software packages the process is similar.
Desaturating Images in Photoshop
|Make sure you are on the duplicate layer and Desaturate the image by clicking Shift + Ctrl U or Image --> Adjustments --> Desaturate|
|Immediately click on Edit --> Fade Desaturate (if this is grayed out, you need to go back to immediately after Desaturating image|