**Q: I forgot to invert my particles (they are black on a white background), and I've already done CTF correction. How can I fix it ?**

**A:**
The following assumes you are using bash or a similar shell. If you use zsh or csh, you may need to alter this a bit:
<code>
cd <the project directory>

for i in `e2bdb.py particles -s`
do
e2proc2d.py $i $i --inplace --mult=-1
done
</code>

That's it. That will invert ALL of your particle data without messing up any of the CTF parameters.