In this guide I am going to walk you through the 3 techniques I employ to white balance (WB) an image. The third method is more comprehensive and the method I use when I’m really taking my time and/or when the WB is really off. The first method is much faster but doesn’t give as good of results and the second method is a blend of the first and third.
Preface
Below is the before/after image that I will be using as a demonstration. To complete the edits on the image following white balancing, please see the article where I walk through my techniques for editing/finishing scanned images. Aside from white balancing, it consists of adjusting contrast/brightness and increasing the sharpness of the photograph.
Final Image 
Before White Balancing
Method 1
This method, as stated above, is a lot faster but does not give as good results. The quality of the WB is lower and it darkens the image too much in my opinion.
The start, open a curves adjustment and using the baster looking icons on the left, select the dark baster to set the “true black” in the image.
While holding down the alt/option key, scroll the dark side of the histogram towards the light side until you start to see some of the image appear. (For B&W images, the histogram is reversed – not that you’d need to WB those images.)
Once you believe you’ve found the “true black” in the image, sample that pixel by clicking on it. Repeat this step to identify and indicate the “true white” of the image using the white baster.
Below is a final draft of the image using Method 1.
Method 2
To start, create a luminosity mask (command + alt/option + 2). Open a curves adjustment (should have applied the luminosity mask as a layer mask) and then duplicate that layer, leaving you with 2 curves adjustments. With one of the curves adjustments, invert the layer mask. (At this step, I usually rename the layers as light and dark.)
On the curves adjustment adjusting the darks, follow the exact same protocol as identified in Method 1 to set the “true black”.
Follow a same protocol for the curves adjustment adjusting the lights. In the end, you should get similar results as to what we got from Method 1 but without the drastic darkening of the photograph.
Method 3
To begin, follow the same initial steps as in Method 2 – create 2 curves adjustments with the layer mask set to be the luminosity mask for the one layer and it’s inverse in the other.
I usually start in opposite order here (for no particular reason) and begin with making adjustments to the light layer. I like to zoom in closer to a part of the frame that tends to be lighter and ideally has some color variation.
Here, I typically leave extreme corners alone and make adjustments in the middle of the curves. As indicated by the arrow, you will find a drop-down menu that allows you to make adjustments to the red, green, and blue layers individually. In a very imprecise way, I usually starting playing around with the curves until I get something that seems alright.
In similar fashion, close in on a selection of the frame that tends to be a bit darker and has some diversity in color. In the other curves adjustment layer, follow a similar protocol and work until you achieve good WB.
It’s not uncommon for me to bounce back and forth between the two curves adjustments and continue to hone in the best WB I can get. After all, it’s a game of balance and as you make adjustments to one layer, the other may get off a little.
FILM PHOTOGRAPHY 