Question

I’m using DruTex, which is a Drupal module to embed Latex equations. The context of the equation is marked, and a Latex interpreter will generate a PNG file:

dvipng -o [IMG_FILE] -D [DPI] -T tight [TMP_DIR]/[HASH].dvi

The dvipng utility is used to generate a PNG from Latex’s DVI file. That’s good so far, but I could need black background and white foreground for these equations, since otherwise they are hard to read, because they appear in a dark-themed way.

convert (from Imagemagick) doesn’t have an -invert flag. Neither does dvipng. So is there a way to invert a png file? I can add something to that routine like:

batch_invert -input [IMG_FILE] -out [IMG_FILE]

However I do not know how I can implement that.

Answer 1

convert has a -negate option that works.

Example:

convert -negate input.png output.png