(03-17-2017, 07:06 PM)rich2005 Wrote: These are the options so far:
1. Probably the one you want as Ofnuts post. Enable the alpha-lock, top of the layers dialogue and fill the layer with black. Everything will be black but the image is still RGB for annotating. Remember to un-toggle the alpha lock for further editing
2. The Color Exchange does what you asked for, changes red to black but leaves other colours.
3. A third alternative is desaturate to shades of grey Colour menu -> desaturate.
These used to be the bane of my life, Full sized drawings shrunk to A3 size for use in the field. Needed a magnifying glass to read the notes.
edit: Just a note but there is a degree of transparency remaining in the red. Can be adjusted if required. http://i.imgur.com/kjb9Ysf.jpg
edit: another day: things are a bit quiet so a 2 minute video demo of using the alpha lock
I followed your video and it works like a charm!