This is a technique, published on the web, involves an RGB channel and as such is not either intuitive or easy to do.
To quote, it says you must wind up with the following layers
1) Original Image on the bottom
2) Copy of original's Blue Channel, colorized to Blue/Cyan (Hue=210 from 360), Opacity~30%, Blend=Difference
So it basically takes a copy of a channel - I used the Blue one (although the Red one would have also worked) and put it on a new layer over the original image (already adjusted by AutoContrast, so that the full tonal range was used).
| this is the blue channel |
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The blend mode, of this new layer, is changed to Difference and the Opacity reduced to 30-50% (I used 50%). Pretty awful!!, but then...
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the Hue/Saturation of this layer Note that the Colorize option is ticked - most important |
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giving this... which is too green, but we could correct that with an RGB curve.
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The layer palette was...
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