Ran the ELE2PNG program in the verbose mode switch -vvv

Loads of interesting / useful info BUT

the last line was quote error distance 324 unquote

just wondering what that was about

If you convert a PNG with colors in it that not exactly match one of the mapped ones, it guesses what mapped color that might be. It does so by means of calculating the euclidean distance between every mapped color and the color of the pixel in the color space (RGB as coordinates). After running through that, it takes the mapped color with the shortest distance.

From all guessed distances, the maximum is displayed as "error distance". However, this distance is the quadratic one, so you have to take the square root of this to get the pixel distance. In your case, one of the colors was 18 away from the nearest mapped color.

I have changed that to a clearer text (and did the square root) already in my current work version.