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Step 10Reverse and burn out
You probably have light coloured tracks on a dark background. What autotrace needs is dark tracks on a light background.
Desaturate the image, that is to say, turn it into greyscale (Colours > Desaturate > Luminosity (or whichever works best)). Next, invert the image (Colours > Value Invert).
If you have a really clear, evenly lit, well focussed picture, this may be adequate, in which case you can go on to the next step. Otherwise, read on...
You need to burn out any detail on the background, which is now light gray or something approaching white, and "dark out" any detail on the tracks, which are now dark gray, or something approaching black. If the picture is badly lit, as mine was, this will by now be very obvious - but it just means you have to work in stages.
To do this, you need to set new black and white points for the image. If you have any area which is very different from the rest, isolate it with a large selection, feather the selection by a large amount (Select > Feather) such as 50 - 100 pixels, and work on it first, so it looks similar to the rest of the board.
Choose the levels dialogue (Colours > Levels). Near the bottom of the dialogue, there is a button marked "Auto" and 3 eye dropper buttons. The eye droppers are to pick the black, grey and white levels. Click the dropper for the white level, and click an area of the original substrate, if you can see any, which is a bit darker than the rest. Don't use the darkest area as this may be too similar to the lightest track area. Click the dropper for the black level, and click an area of track which is lighter than the rest, if you can find any. Don't use the lightest area as this may be too similar to the darkest substrate area. Click OK. Repeat as often as you need to to get nice black or nearly black tracks on a nice white, or nearly white, background. Choose areas carefully to ensure that no tracks get blurred together or pinched through.
If you find that some area you did has become harsh and jaggedy at the edges, undo until it looks right again, and work on the remaining areas of the board by selecting and feathering as described above.
Paint in/out any unwanted details like writing, artefacts and the dots in the holes if you can see them. You may find some bits of track have become blurred together or pinched through - paint in repairs with a soft brush.
Copy the alignment marks to the layer, and save a copy to a new .png file.
Desaturate the image, that is to say, turn it into greyscale (Colours > Desaturate > Luminosity (or whichever works best)). Next, invert the image (Colours > Value Invert).
If you have a really clear, evenly lit, well focussed picture, this may be adequate, in which case you can go on to the next step. Otherwise, read on...
You need to burn out any detail on the background, which is now light gray or something approaching white, and "dark out" any detail on the tracks, which are now dark gray, or something approaching black. If the picture is badly lit, as mine was, this will by now be very obvious - but it just means you have to work in stages.
To do this, you need to set new black and white points for the image. If you have any area which is very different from the rest, isolate it with a large selection, feather the selection by a large amount (Select > Feather) such as 50 - 100 pixels, and work on it first, so it looks similar to the rest of the board.
Choose the levels dialogue (Colours > Levels). Near the bottom of the dialogue, there is a button marked "Auto" and 3 eye dropper buttons. The eye droppers are to pick the black, grey and white levels. Click the dropper for the white level, and click an area of the original substrate, if you can see any, which is a bit darker than the rest. Don't use the darkest area as this may be too similar to the lightest track area. Click the dropper for the black level, and click an area of track which is lighter than the rest, if you can find any. Don't use the lightest area as this may be too similar to the darkest substrate area. Click OK. Repeat as often as you need to to get nice black or nearly black tracks on a nice white, or nearly white, background. Choose areas carefully to ensure that no tracks get blurred together or pinched through.
If you find that some area you did has become harsh and jaggedy at the edges, undo until it looks right again, and work on the remaining areas of the board by selecting and feathering as described above.
Paint in/out any unwanted details like writing, artefacts and the dots in the holes if you can see them. You may find some bits of track have become blurred together or pinched through - paint in repairs with a soft brush.
Copy the alignment marks to the layer, and save a copy to a new .png file.
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