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How to convert an infrared photograph to black & white using Gimp - When you take infrared photographs with a digital camera in the normal colour shooting mode they are processed with a red colour cast. Here's how you remove the cast using Gimp.
Infrared photography is a very effective way to create an eerie, ghostly image. However, how do you get from your original version of the picture to that ghostly greyscale that is so characteristic of infrared photography? There are a few ways to achieve this, but here Michael Bates is going to detail the method, using Gimp, that gives you the greatest control over the process and subsequently over your end result.
Step 1 Open your infrared image and Duplicate the ‘Background’ layer. This is just a precautionary measure to make sure you can undo any changes and restart from the base image if you desire. Double-click the name of the new layer to rename it, change its name to something useful, here ‘BW’ will suffice to remind us that this is the layer we are going to make black and white.
Step 2 In the ‘BW’ layer open the Colours menu along the top of the image window, then move your mouse down to Components and select the Channel Mixer, which will open a new window. The first thing we want to do in here is to select the ‘Monochrome’ option, then we will balance the sliders to get an exposure we like. We want something with blacks and whites present, but try not to blow-out the highlights.
Step 3 Although the picture is greyscale now it will most likely be lacking contrast and definition, so to try to reverse this open the Filter>Enhance>Unsharp Mask window from the Image window. This tool selectively sharpens the image based on the differences in colour that are present; where there is a clear difference in colour this tool will sharpen the distinction.
You will be presented with a series of options, once again play around until you get the effect you like; the Radius option affects the size of the area sharpened, the Amount will control just how sharp any areas the tool sharpens will be made, and the Threshold determines how large the difference between colours has to be for the definition to be sharpened.
Step 4 The final tweak the image needs to really make your picture stand out is with the Colours>Brightness-Contrast tool. So open this, and increase/decrease the contrast until you have both blacks and whites present in the image; you may have to alter the brightness after changing the contrast to counteract any murkiness or overexposure.