White Balance, Gimp tutorial
Tutorial for automatic and manual white balance correction with Gimp.
In photography, a correct white balance is used to counter possible unrealistic colors taken by the camera. Gimp can fix an incorrect white balance with two tools, Automatic White Balance and Color balance. Each source of light has a different color radiation: Light of a candle has red tones, a snowy picture before the sunrise will have blue tones. To counter this dominant, the camera software use a filter of the opposite color in order to neutralize the dominant.
White is the most easy color to identify, here comes the name "white balance".
Next you can see an example, on the left you can see the "counter" color, on the right the color of the light.
Gimp allows us to balance the colors of an image automatically or manually. In the following example photograph, I set the white balance on incandescent light on the camera, but the scene was taken in daylight, so the colors has a blue tone (the camera used a blue filter for counter the red of tungsten light, but the light was white, so the result is a wrong white balance).
You can try to correct the white balance with Colors - Automatic White Balance. This tool modify the histogram of each color, and simply assign to all the same length. The results are generally good, but you will have a more contrasted image. If you need to keep a low contrast on your photo, you must proceed manually.
If you want to proceed manually, or you are not satisfied from the
results of the automatic white balance, you can proceed manually.
Open Colors - Color Balance, for each one of the three colors you can
work on the Shadows, midtones or highlights. Generally i edit only the
midtones. If your photo is too red, you can adjust the white balance,
by moving the cursor to Cyan.
For each color dominant the cursor must be moved in the opposte way (move to magenta, if the dominant is green, ecc.. ecc..)
There are a couple of things to know for a perfect white balance:
1) The best results are when you choose the right balance on the camera, Gimp should be used only for minor adjustments.
2) Your eyes are really fast to "autobalance", when you have finished to edit the white balance, take a couple of minutes for do other things, than check your image again. This is an animated example of before/after white balance.
As you can see in the animation above, the results are great.
You can use Color balance for enhance a dominant. Next you can see two examples photos, one cold and one warm, where the dominant has been pronounced with the color balance tool.
As you can a right white balance is really important for the result of the photo.
There is only another thing that i want to write before the end.
If you need to shoot a photo with a strange or unknown illumination (For example a mix of neon, tungsten, daylight) you should choose the raw format, if your camera is able to shoot it.
Raw format saves the raw data of the image, and let you modify the white balance in post production with the complete control. Anyway in the most of the cases your camera is able to choose right white balance in automatic.
Thanks to Cody B. for errors report.