Finding Neutral Grey in an Image

As I wait for my studio to get finished (heater is going in as we speak!) so I can start providing some studio lighting information here is a useful little technique to find the neutral grey point in your image.  Create a new blank layer and fill it with 50% grey change the blending mode to 'difference'  Whoa!  Some funky business, eh?  What this basically did was show us where the neutral grey point is.  You see, any color that matches 50% grey (or darn close) will become black.  All the other colors aren't the grey we are after.  Now you need to create a 'threshold' adjustment layer and move the slider all the way to the left--you should see a white screen. This is going to allow us to find that black point in the image that our previous step created.  I like to highlight the number and use my 'up arrow' key to move the slider just until I start to see the first bits of black show up on the screen.  Click OK on that adjustment layer. Zoom into those spots.  Now create a 'curves' or a 'levels' adjustment layer and select the grey eyedropper in the dialogue box.  Place the eyedropper on the black area and then you can click OK on the adjustment layer.  Deleted the 'threshold' and the 'difference' layers and toggle the curves/levels adjustment layer on and off so you can see what you have done.

If your adjustment looks good to your eye then you can merge that layer down or whatever you normally do.  You can also adjust the opacity of the layer to suit.  If there is no truly neutral grey in the image this technique may mess up your colors a little bit or you may just not like the adjustment on this particular image.  If that is the case then you can just delete the adjustment layer and move on.  I am assuming a certain competence with Photoshop here in that you know how to do all of those commands and where to find the respective tools.  If you don't, please shoot me a message and I'll gladly help you out in more detail.