How to Correct Color Cast from Poor White Balance in Photos with GIMP

Correcting White Balance with GIMP
Text and Images © Ian Pullen

Digital cameras are versatile and can be set to automatically select the best settings for most situations to ensure that the photos you take are as high quality as possible. However, in some cases they may have problems in selecting the correct white balance setting.

GIMP—short for GNU Image Manipulation Program—is open source image editing software that makes it relatively easy to correct white balance.

How White Balance Affects Photos

Most light appears white to the human eye, but in reality, different types of light, such as sunlight and tungsten light, have slightly different colors, and digital cameras are sensitive to this.

If a camera has its white balance set incorrectly for the type of light it is capturing, the resulting photo will have an unnatural color cast. You can see that in the warm yellow cast in the left-side photo above. The photo on the right is after the corrections that are explained below.

Should You Use RAW Format Photos?

Serious photographers will proclaim that you should always shoot in RAW format because you are able to easily change the white balance of a photo during processing. If you want the best photos possible, then RAW is the way to go.

However, if you're a less serious photographer, the additional steps in processing RAW format can be more complicated and time-consuming. When you shoot JPG images, your camera automatically handles many of these processing steps for you, such as sharpening and noise reduction.

01
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Correct Color Cast with Pick Gray Tool

Using Levels Pick Gray Tool to Correct Color Cast
Text and Images © Ian Pullen

If you have got a photo with a color cast, then it will be perfect for this tutorial. 

  1. Open the photo in GIMP.
  2. Go to Colors > Levels to open the Levels dialog.
  3. Click the Pick button, which looks like a pipette with a gray stem. 
  4. Click on the photo using the gray point picker to define what is a mid-gray tone. The Levels tool will then make an automatic correction to the photo based on this to improve the color and exposure of the photo. 

    If the result doesn't look right, click the Reset button and try a different area of the image.
  5. When the colors look natural, click the OK button.

While this technique may lead to more natural colors, it is possible that the exposure may suffer a little, so be prepared to make further corrections, such as using curves in GIMP.

In the image to the left, you will see a dramatic change. There is still a slight color cast to the photo, however. We can make minor corrections to reduce this cast using the techniques that follow.

02
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Adjust Color Balance

Using Color Balance and Hue-Saturation to Tweak the Color
Text and Images © Ian Pullen

There is still a little bit of a red tinge to the colors in the previous photo, and this can be adjusted using the Color Balance and Hue-Saturation tools.

  1. Go to Colors > Color Balance to open the Color Balance dialog. You'll see three radio buttons under the Select Range to Adjust heading; these allow you to target different tonal ranges in the photo. Depending on your photo, you may not need to make adjustments to each of the Shadows, Midtones, and Highlights.
  2. Click the Shadows radio button.
  3. Move the Magenta-Green slider a little to the right. This reduces the amount of magenta in the shadow areas of the photo, thus reducing the reddish tinge. However, be aware that the amount of green is increased, so watch that your adjustments don't replace one color cast with another.
  4. In the Midtones and Highlights, adjust the Cyan-Red slider. The values used in this photo example are:
  • Shadows: Magenta-Green 10
  • Midtones: Cyan-Red -5, Magenta-Green 5
  • Highlights: Cyan-Red -6, Magenta-Green 6

Adjusting the color balance has made a minor improvement to the image. Next, we will adjust the Hue-Saturation for further color correction.

03
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Adjust Hue-Saturation

Using Hue-Saturation to Correct a Color Cast
Text and Images © Ian Pullen

The photo still has a slight red color cast, so we'll use Hue-Saturation to make a minor correction. This technique should be used with some care as it can accentuate other color anomalies in a photo, and it may not work well in every case.

  1. Go to Colors > Hue-Saturation to open the Hue-Saturation dialog. The controls here can be used to affect all the colors in a photo equally, but in this case we only want to adjust the red and magenta colors.
  2. Click on the radio button marked M and slide the Saturation slider to the left to reduce the amount of magenta in the photo.
  3. Click the radio button marked R to change the intensity of the red in the photo.

In this photo, magenta saturation is set to -19, and the red saturation to -29. You should be able to see in the image how the slight red color cast has been further reduced.

The photo isn't perfect, but these techniques can help you salvage a poor quality photo.

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