Tweety's image is rough and jagged because there is no antialiasing in the image. I tried the Antialias filter (Filters / Enhance) and it didn't do anything.

I tried PhotoComix's Smoothing Filter in G'MIC and it did a commendable job of antialiasing the layers. I had the Amplitude set at 4.

Here's Tweety before and after using PC's filter.



Here is where I semi-flattened both animations. As you can see, on the left there is no white semi-flattening. On the right, you can see the semiflattening of the antialiasing made by PhotoComix's filter.

It works well. Did you draw Tweety?

No, but I wish I did.

I wish I could draw things like that.

Which filter was that? I love PC's thin brush smoothing. Very handy for removing banding and if used with a little sharpening afterwards, makes a great fake painting.

I like PC's anisotrophic smoothing preset too O. Use it a lot to create various effects to smootho out b/w sketch (G'MIC) to make it look like smoke. Also sometimes blend it with the original to take the edge off the original but still keep it sharp.

That does work very well.

It's in G'MIC > Testing > PhotoComix > PhotoComix Smoothing.

For antialiasing, the amplitude should be set somewhere between 2 & 6. Depending on the image and what looks best.