Remove a Color Cast Part II (Threshold Layer)

In my January 27th post I described a way to remove a color cast by using Blur Average to establish an overall average color for a copy of the image, then switching to the original image and using a middle gray eyedropper in a Levels adjustment to sample the averaged image to reset middle gray in the original. This is a simple method that works in many but not all situations. There are times when a color cast is desirable. Sunsets/Sunrises, fireworks, night scenes, etc usually do not need or do not benefit from color balance correction.

Another method I often use actually does two things in one step. It balances the color to neutral and it also establishes a complete tonal range for the image, ensuring that there are black and white areas. The typical candidate for this image is one that has a color cast and is properly exposed, but has a histogram that is completely between and not touching the boundaries. By using a threshold adjustment layer it is easy to find pure black and pure white, then use the sampling eyedroppers in either Levels or Curve adjustment layer to set the corresponding black and white points. In the process of doing this any color cast will usually be removed. The resulting image will have a full tonal range, from pure black to pure white.

Here is a quick how to.

In this image of the Bow Bridge in Central Park, there is an overall warm cast, no black and no white in this image, making it appear dull and drab. In Photoshop, I start by creating an adjustment layer,

Select Threshold type,

giving me a layer that looks like this.

There is an adjustment slider that I will move left or right to find the threshold of black and white levels.

Next, I select the Color Sampler tool, and set the Tool Options to 11x11 average,

then I go back to the adjustment panel for the threshold layer and move the slider all the way to the left until the image turns completely white, then I move the slider slowly to the right until I start to see the first black areas,

sometimes it helps to zoom in so I can be sure to place my Color Sampler tool entirely in the black area,

it is important to reveal just the first area that shows up - the threshold of black - to ensure that I will get the smallest area of black. I use the Color Sampler eyedropper tool and click in the black area. This will leave a non-printing marker that will I will use later.

Now I repeat but this time moving the slider to the right to find the white point, dropping a marker on the white point. After selecting the two points I no longer need the threshold layer, so I can either turn it off or delete it.

Next I create another adjustment layer, either Curves or Levels. Either will provide eyedroppers that will be used to select the black and white points that I left reference markers on in the previous step. Using the black or topmost eyedropper to pick on the black point, and the bottom one to select the white point.

The image looks like this after setting the black and white points.

and for reference, this is the before view.

everything is more pleasing, there is a full range of tones, and the colors look better without the greenish/yellowish cast. Sometimes the effect is subtle, at other times it can be pretty dramatic. Hopefully you can use this technique to add a little more WOW! to your images.