Request: filters for PNG32

[DanMan]

There are 2 filters that I like to use when optimizing the filesize of high-color PNGs:

1. Posterize to reduce the number of colors
2. Dithering to reduce the harshness of the posterize filter (which actually increases filesize again)

Would be nice, if those were available for the 32bit PNGs.

[DanMan]

I've tried my hand at posterizing but I'm running into the issue that once it has been posterized at …say 2, turning posterization back up to …say 100 has no effect on the preview (and I guess on the saved image).

How would I go about applying a filter to the image (layer?) before sending it through the saving procedure?

Edit: Ok, so I did what the JPEG export does: duplicate it (to get a new image) and then flatten it (to get a new layer). No idea if that's any good, but at least it works.