White Balance Correction Part 1 (Blue Cast)

White Balance Correction Part 1 (Blue Cast)

Mid-range digital cameras have a feature which allows one to select from multiple presets for the white balance settings, such as "Auto WB", "Tungsten", "Florescent", "Custom Setting" etc. If the setting is not at "Auto WB" then it is easy to make mistakes and leave the last settings on. For example "Tungsten" used in in-door photography will produce a bluish cast when taking a photo out-door.

First start up Gimp and click on "File->Open". The picture on the left shows a distinctive blue cast, as if everything is viewed with a bluish filter. Notice even the shadow on the floor is blue !

The first step is to correct the blue cast using Gimp's Curves Tool.

With the cursor anywhere inside the image window, right mouse click once to bring up the cascading menu table as shown on the left.

Move the mouse cursor to higlight "Image", then move right to highlight "Colors" and finally move right again to highlight "Curves"

This way of accessing the menu structure in Gimp is frequently represented by a short hand "Image->Colors->Curves"

In the Curves Tool, click on the toggle button at the top until it says "Blue". Next click on the mid point of the curve and drag it gently downwards.

As you drag down, notice the image becomes less saturated in blue, stop when a little bit of greenish cast starts to creep in.

Finally click on the toggle button at the top of the Curves Tool until it says "Red"

To remove the green cast, click at the middle portion of the curve and drag it gently upwards, until the green cast is gone. Stop just before the red creeps in.

Click "OK" to apply the changes to the image and dismiss the Curves Tool window.

The final image have the blue cast removed and all the beautiful colors restored. Right mouse click inside the image window and click on "File->Save" to save the picture.

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