There are various ways to correct the white balance of an image. However this one his one is one of the most technically correct results for getting right white balance. Ideally you should use gray card or colour checker while shooting itself, this blog will tell a method for situation where gray card method is not feasible ,i.e., wildlife.
Disclaimer: There is no compulsion to correct the white balance, if you wish to show mood in image, leave it as such.
STEP 1: For better result, work on 16 Bits/Channel.
STEP 2: Copy current layer by dragging the current layer (merged/pixel) to new layer OR press Clt +(Cmd)+Alt+Shift+N
STEP 2: Fill this new layer with 50% Gray.
Edit>Fill>Contents=50% gray layer
STEP 3: Change the blending mode to difference. Image looks different, no worries
STEP 4: Open threshold layer for finding gray pixel. Understand the concept. When you subtract any pixel with gray (R,G,B=128,128,128) with gray you will get 0,0,0 means black, isn't it? Here using threshold layer we will try to find black pixel. In previous step we changed the blending mode to Difference, which subtract the gray with layer below.
STEP 5: Now drag the threshold slider to left, until you see clusters of black pixels. Don't go to extremes.
STEP 6: Now in this step, we will sample the near gray/gray pixel. Open Colour Sampler Tool from Toll Panel.
STEP 7: Now click on black clusters of image to sample the color.
STEP 8: Delete Threshold Adjustment Layer and New Layer (Layer-1).
STEP 8: Open Curve adjustment Layer, you will see curve dialogue box
STEP 8: There are three pens to sample White, Gray and Black. We will use Gray Pen to fix the White Balance in next step.
STEP 8: Pick the Gray Pen from Curve
STEP 9: Pick the Gray Pen from Curve, Click once on the gray point eyedropper icon in the Curves to select it. Next locate the gray Color Sampler point we created in earlier step and click once directly on it to set the gray point.
STEP 10: Click once on the gray point eyedropper icon in the Curves dialog box to select it. Next locate the gray Color Sampler point we created earlier and click once directly on it to set the gray point.
You are done, White Balance Corrected. Yupppi!!!