One of the things that Photoshop is used for is removing color cast. Color cast is color contamination in the neutral areas of your pictures. By neutral areas, we mean parts of the picture that are white or light gray (white shirt, clouds, white of the eye, etc.) , black or dark gray (shadows, the pupil of the eye, hair, black shirt, etc,) or middle gray (cemented wall, etc.) . When neutral areas exhibit a color cast, chances are the picture as a whole has a color cast as well. If the color contaminations orange, then the picture will have an overall orange look.
There are many causes of color cast. One of them is a wrong White Balance setting in your digital camera. If the White Balance in your digicam is set to daylight (sunny) and then you take a picture under tungsten light (ordinary house light) indoors, then your picture will have an orange appearance particularly in the white areas (hence the term “White Balance”). Photoshop offers an array of techniques to remove a color cast. I will illustrate here one of the techniques that are very easy to follow.
Understanding the Color Wheel
To understand how Photoshop operates, you must have an understanding of the color wheel. In the color wheel, the complement of Blue is Yellow. That means if the picture has a bluish cast, then the yellow component in the picture is weak. To remove the bluish cast, all you have to do is increase the yellow in your image. Photoshop’s Color Balance command shows you the relationship of the colors on the color wheel. In fact, Color Balance is one of the commands that you can use in correcting the color in your image.
Let me now demonstrate the Inverse Color Technique as a quick and “dirty” way of removing color cast.
Step One: Open the File
Open a file that has a color cast. Make sure that the Info palette is visible. The upper portion of the Info palette is divided into two columns with RGB-values readout. Set the first column in RGB and the second in HSB. (To change the setting, click on the small eyedropper to access the drop down menu). You need the HSB setting to enable you to choose a neutral area in the picture that has a brightness level of 50% and the Info palette will help us locate that area. By choosing an area with a brightness level of 50% in your picture, you are assured that the luminosity of your image will not change when you apply the technique.
Step Two: Place a Color Sampler
Next, get your Color Sampler tool from the toolbox and place it on the image. The moment you’ve placed it, the Info palette will expand to show you the RGB readout. Move it around until you get a reading of 50% brightness in the HSB column of the Info palette.
Step Three: Sample the Color Cast
After locating that neutral area that has 50% brightness level, get the Eyedropper tool from the toolbox and click on the Color Sampler to sample the color. Make sure that the Sample Size option of the Eyedropper in the Options palette is set to 3 by 3 Average to get a more accurate sample. The color that you sampled is the color cast and should appear in the Foreground Color box in the toolbox.
Step Four: Create a New Layer
Create a new layer on top of the Background and fill it with the foreground color (the color cast). You can press Option-Delete (PC: Mt-Backspace to fill a layer or selection with the current Foreground color.
Step Five: Inverse the Color
Choose Image > Adjustment> Invert on the menu. This will invert the sampled color to its exact opposite color 0. Remember, to remove the color cast you have to introduce its opposite color. Now, the top layer is hiding the Background.
Step Six: Change the Blending Mode
Apply a blending mode to apply the opposite color to the color cast. You can use Overlay, set to 100% opacity. I find that Linear Light, set to about 50%, gives a more accurate result 0.
Step Seven: Improve the Contrast
It is my experience that, after removing the color cast using this technique, an image loses some of its contrast. To bring back the contrast in your picture, click the Adjustment Layer button in the Layers palette and choose Curves. Adjust the diagonal line in the Curves until you get the contrast you like.