How to Correct White Balance with GIMP

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Correcting White Balance with GIMP

Correcting White Balance with GIMP
Text and Images © Ian Pullen

Editor's Note:

GIMP is an open source project.  Though GIMP has been around for several years I would suggest you treat it with the same caution you would with any other open source software. If you wish to try is out you can download the Mac , Linux and Windows installer from the GIMP website.

It is relatively easy to correct white balance in GIMP using the Levels tool and a couple of other features to fine tune the result. Modern digital cameras are remarkably clever and are able to 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.

Keeping things simple, the white balance of a digital camera affects how colors appear in 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. The result is that 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 left hand photo on this page, that has a warm yellow cast. The photo on the right shows it after the corrections that are demonstrated on the following pages.

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, but if you're a less serious photographer, the necessity to also undertake the other steps in processing can make RAW more complicated and time consuming. That's because when you shoot JPEGs, your camera automatically undertakes a lot of these processing steps for you, such as sharpening and noise reduction.

Manually sharpening and reducing noise using GIMP and other image editors is relatively straight forward, however most users do not consider it so easy to correct the white balance of JPEGs. In the following few pages, I'll show how a few simple features in GIMP will help you to correct white balance to achieve impressive results. These steps will also help you to understand how the Levels tool and Color Balance and Hue-Saturation features operate.

What is a digital camera raw file?
• White Balance in Photography
• Color Temperature in Photography

02
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Using Levels Pick Gray Tool to Correct Color Cast

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

Hopefully all your photos will have a perfect white balance and not need correcting, but if you have got a photo with a color cast, then it will be perfect for this tutorial. I've taken a quick snap with a compact camera under artificial light using a white balance setting for shade. This has resulted in a photo that looks unnaturally warm in tone – you can download a copy of this photo to work on yourself [Download: original.JPG]. The Levels tool will allow us to correct white balance in GIMP quickly and easily.

Open the photo that you want to correct in GIMP and then go to Colors > Levels to open the Levels dialog. You can ignore most of the controls in the Levels dialog as it isn't important to understand them for this tutorial. The important feature for now is the Pick gray point button that is represented by a pipette with a gray stem – it's the middle of three similar buttons and is marked on the accompanying image.

You can use this gray point picker to click on the photo and tell the Levels tool 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 you look at the photo, you can see where I clicked with the cursor and on your photo you want to look for an area that looks roughly like a mid gray tone.

If the result doesn't look right, then just click the Reset button and try a different area of the image. When the colors look more natural, click the OK button. Do note that 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 Brightness-Contrast or curves.

If you compare the image on this page with the previous page, you will see a dramatic change with this one looking much more natural. In some cases that may be enough, but I think there is still a slight color cast to my photo and I'm going to show another couple of techniques for making minor corrections to reduce this cast on the next two pages.

Make Your Photos Better Using GIMP Levels

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Using Color Balance and Hue-Saturation to Tweak the Color

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

The corrections I made on the previous page made a big improvement to the photo, but I think there is still a little bit of a red tinge to the colors. I'm going to use the Color Balance and Hue-Saturation tools to tweak the colors a little more.

Firstly go to Colors > Color Balance to open the Color Balance dialog. You'll see three radio buttons under the Select Range to Adjust heading and 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, but in my case I tweaked all three.

Firstly I clicked the Shadows radio button and then moved the Magenta-Green slider a little to the right. This reduces the amount of magenta in the shadow areas of the photo, so reducing the reddish tinge. However be aware that in so doing, the amount of green is being increased, so be careful your adjustments don't replace one color cast with another one. In the Midtones and Highlights, I also made adjustments to the Cyan-Red slider. The actual values I used are as follows, but these will vary from photo to photo.

Shadows: Magenta-Green 10
Midtones: Cyan-Red -5, Magenta-Green 5
Highlights: Cyan-Red -6, Magenta-Green 6

This has helped to make a minor improvement to the image and on the next page I'll show how using Hue-Saturation can also make a further color correction.

• Split Tone With Color Balance in GIMP for Creative Tinting Effects

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Using Hue-Saturation to Correct a Color Cast

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

I feel that my photo still has a slight red color cast and I'm going to show how you can use Hue-Saturation to make a minor correction for a color cast. 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.

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 I just want to adjust the red and magenta colors. If you click on the radio button marked M and then slide the Saturation slider to the left, you will reduce the amount of magenta in the photo. The radio button marked R allows you to change the intensity of the red in the photo. In my photo, I reduced the magenta saturation to -19 and the red saturation to -29 and you should be able to see in the image how the slight red color cast has been further reduced.

The photo isn't perfect and it would be better to get the best possible photo straight from your camera. However it is a big improvement and in cases where you don't have the option to take a photo again, these techniques can help to salvage a poor quality photo.

• Change the Color of Digital Papers with Hue-Saturation in GIMP