Sometimes, after you take a picture, it appears too cold or blue. GIMP, a free open source image editor, has advanced tools that can make the picture's color temperature warmer. The tools in this graphics software are very sensitive, so adjust them with care and precision. If used properly, GIMP's color editing tools can remove the bluish cast from your picture and replace it with warmer tones of red, magenta and yellow.
Open your picture in GIMP. Select "Colors" and "Color Balance" from the menu. Make sure that "Preserve Luminosity" and "Preview" are checked. Under "Select Range to Adjust," select "Shadows," "Midtones" or "Highlights." Under "Adjust Color Levels," move the top slider slightly toward red, the middle slider slightly toward magenta and the bottom slider slightly toward yellow. Preview your image in the main window. Move the sliders back a bit if the picture develops a red, magenta or yellow color cast. Click "OK."
Select "Colors" and "Hue-Saturation." Under "Select Primary Color to Adjust," click the radio button beside blue. Again, ensure that "Preview" is checked. Then move the "Saturation" slider to the left. Repeat this step with cyan. Select red, magenta and yellow in sequence, and adjust the saturation sliders slightly to the right.
Adjust the hue of each color within the "Hue-Saturation" tool, if necessary. Move the hue sliders for blue, cyan and magenta slightly to the right. Move the red and yellow hue sliders slightly to the left. If a color cast appears, move the sliders back toward the zero position. Click "OK."
Select "Colors" and then "Brightness and Contrast." If the picture looks dark with intense shadow, move the brightness slider to the right and the contrast slider to the left. If the picture seems to have a white film over it, move the brightness slider to the left and the contrast slider to the right. Click "OK."
Click "File" and "Save As." Type a new name to preserve your original picture. Click "Save." If prompted, make any adjustments necessary to the file and then click "Save" again.
Uncheck and recheck the button beside "Preview" to see how your picture has changed from the original version. Typing numbers in the fields, or using the up and down arrows beside the input values, gives you more control over the corrected picture. There is also color temperature plugin that you can download and install in GIMP (see Resources). Copy the plugin to the "Scripts" folder in GIMP's program files, then click "Filters," "Script-Fu" and "Refresh Scripts." The color temperature script appears under "Colors" and "Convert Color Temperature" in the "Filters" menu. Move the "Target Temperature" to the left a bit, then adjust the intensity and saturation up and down as needed.