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Step 9Clean the tracks
You are almost ready to process the image using AutoTrace!
You need the tracks to have good clean edges and smooth colour, or else AutoTrace will put in all sorts of details that you don't want and probably didn't even see, since it traces a little bit too well.
I spent many, many hours trying to do this by selecting areas of track or substrate with the fuzzy select tool and using some method to smooth the edges. If you are interested in reading a discussion about methods for doing this, please see this this thread: http://registry.gimp.org/node/14912 . I found that any method that gave me something like a smooth edge also led to rounded off corners and pinched off track ends. The idea was that I could then use the bucket fill tool to even out the tracks and substrate.
The best way to smooth out the unwanted detail is to trace the image using a different tracing program - I used Inkscape, which unfortunately doesn't also offer centre line tracing. Some cleaning up still needs to be done first though.
Smooth out the fine detail using the selective gaussian blur tool (Filters > Blur > Selective Gaussian Blur). What this tool does is apply a blur which is limited, or "fenced in" by areas of high contrast. You can also use the wavelet decompose tool and delete the top (fine detail) layer, however this may also remove details you want to keep.
I used a high radius of 30 pixels, and a max delta of 29. These figures will likely be different for you. I found these by setting a very high blur radius, turning up the delta until all the detail disappeared, then turning it down again until I could see the tracks clearly, then turned down the blur radius to a saner level, judged from the sizes of the tracks in pixels. Press OK. You should now find any "blockiness" in the tracks has been blurred out, but they are still clearly tracks.
Use the eyedropper tool (toolbox, 2nd row 3rd icon from left) to pick an average colour from the remaining areas of substrate. If the lighting is uneven, pick one of the lighter areas (probably not the lightest though). Set a few pixels spread for the eyedropper. This will set the foreground colour.
Create a new layer, setting it to be filled with the foreground colour, and move it below the layer you are working on. Most of the substrate should now be indistinguishable from the newly created background.
Create a new layer from visible. You should probably save this layer as a new image.
I found at this point I could see quite a bit of spread due to optical aberration at the edges of some of the tracks which were very close together, so I set guides along them and used a small soft brush to paint background colour along these.
I also painted in the track holes in the track colour, but I'm not sure that this is necessary - it may be sufficient just to remove the dot of the actual hole in the middle.
Manually do any other cleaning up at this point. Don't worry about light coloured marks on the actual tracks, or dark ones on the substrate, as these are going to get burned out.
You need the tracks to have good clean edges and smooth colour, or else AutoTrace will put in all sorts of details that you don't want and probably didn't even see, since it traces a little bit too well.
I spent many, many hours trying to do this by selecting areas of track or substrate with the fuzzy select tool and using some method to smooth the edges. If you are interested in reading a discussion about methods for doing this, please see this this thread: http://registry.gimp.org/node/14912 . I found that any method that gave me something like a smooth edge also led to rounded off corners and pinched off track ends. The idea was that I could then use the bucket fill tool to even out the tracks and substrate.
The best way to smooth out the unwanted detail is to trace the image using a different tracing program - I used Inkscape, which unfortunately doesn't also offer centre line tracing. Some cleaning up still needs to be done first though.
Smooth out the fine detail using the selective gaussian blur tool (Filters > Blur > Selective Gaussian Blur). What this tool does is apply a blur which is limited, or "fenced in" by areas of high contrast. You can also use the wavelet decompose tool and delete the top (fine detail) layer, however this may also remove details you want to keep.
I used a high radius of 30 pixels, and a max delta of 29. These figures will likely be different for you. I found these by setting a very high blur radius, turning up the delta until all the detail disappeared, then turning it down again until I could see the tracks clearly, then turned down the blur radius to a saner level, judged from the sizes of the tracks in pixels. Press OK. You should now find any "blockiness" in the tracks has been blurred out, but they are still clearly tracks.
Use the eyedropper tool (toolbox, 2nd row 3rd icon from left) to pick an average colour from the remaining areas of substrate. If the lighting is uneven, pick one of the lighter areas (probably not the lightest though). Set a few pixels spread for the eyedropper. This will set the foreground colour.
Create a new layer, setting it to be filled with the foreground colour, and move it below the layer you are working on. Most of the substrate should now be indistinguishable from the newly created background.
Create a new layer from visible. You should probably save this layer as a new image.
I found at this point I could see quite a bit of spread due to optical aberration at the edges of some of the tracks which were very close together, so I set guides along them and used a small soft brush to paint background colour along these.
I also painted in the track holes in the track colour, but I'm not sure that this is necessary - it may be sufficient just to remove the dot of the actual hole in the middle.
Manually do any other cleaning up at this point. Don't worry about light coloured marks on the actual tracks, or dark ones on the substrate, as these are going to get burned out.
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