Precise Color Cast Correction With Gray Fill Layers

Today food blogger Danny Jauregui of Food Bloggers Unite! gives us a great tutorial for neutralizing color casts in images. Click to enlarge most images in this tutorial.

Neutralizing a color cast can be one of the most difficult jobs in post-production. The problem I most often have is realizing that my image has a color cast, but not being able to identify which color is causing the cast! Is it magenta or red? Blue or cyan?

This simple tutorial solves this problem by finding neutral gray in the image, thereby removing the need to guess the color. In order for this trick to work however, your image MUST contain 50% gray tone somewhere in the image; otherwise the color correction will be off.

Step #1 – Add 50% Gray Fill Layer

Open your image and add a 50% fill layer by going to the bottom of the layer palette and clicking the ‘new layer’ icon. Next, on the top menu go to Edit> Fill> 50% Gray.

Step #2 – Change Layer Mode

Using the ‘Difference’ layer mode we will next find pixels in our image that are 50% gray. The ‘Difference’ mode is a comparative layer mode that will invert pixels containing 50% gray, turning those pixels black.

On the layer palette click the drop down menu containing the layer modes found on the upper left corner of the layer palette and change the mode of the gray layer from ‘Normal’ to ‘Difference’. Your image should now look like a funky negative. This layer is designed to help us find the 50% gray pixel only. It will be discarded once this is done.

Step #3 – Mark Gray Pixel with Eyedropper Tool

Select the eyedropper tool from the tools palette and zoom in very close to your image. I zoomed in 600%. The goal here is to find a pixel that is completely black. Once you’ve located a black pixel, hold the shift button down on your keyboard and click the eyedropper tool on the black pixel. This will add a marker identifying the 50% gray pixel.

Next, discard the gray/difference layer by clicking and dragging it to the trash on the bottom of the layer palette.

Step #4 – Neutralize Cast With Levels Adjustment

Now for the correction. Add a ‘Levels’ adjustment by clicking the adjustment layer button at the bottom of the layer palette. A selection of adjustments will appear. Select ‘Levels’.

A dialogue box will appear showing you the image histogram. On the lower right corner you will see three eyedropper icons. Click the middle eyedropper icon and move the cursor over to your image. This middle eyedropper tool sets the gray point, thereby shifting the color balance in the image.

Since we’ve already determined where our gray point is, all you have to do is place the mouse over the marker making sure that both points are precisely matched up. Because the default icon is an eyedropper, I find it hard to be accurate, so I change the icon to a crosshair by simply hitting the caps lock button on my keyboard. Once the two crosshairs are perfectly matched up all you have to do is click the mouse and the color should shift and neutralize.

Danny Jauregui is a Los Angeles based food blogger. His blog Food Bloggers Unite! is a one-stop resource for beginning food bloggers that focuses on food photography.