Making an image a negative

Have some white typeface on black background images (.jpgs).
Want to reverse to make black type on white background.
Seems that a simple filter should be able to do this but cannot find anything.
Any way to do this in Acorn?

You want the Filter ▸ Color Effect ▸ Color Invert filter.

If the text is in a separate layer than the background you will need to apply the Color Invert filter to both layers.