How to convert image.RGBA (image.Image) to image.Paletted?

I'm trying to create an animated GIF from a series of arbitrary non-paletted images. In order to create a paletted image, I need to come up with a palette somehow.

// RGBA, etc. images from somewhere else
var frames []image.Image

outGif := &gif.GIF{}
for _, simage := range frames {
  // TODO: Convert image to paletted image
  // bounds := simage.Bounds()
  // palettedImage := image.NewPaletted(bounds, ...)

  // Add new frame to animated GIF
  outGif.Image = append(outGif.Image, palettedImage)
  outGif.Delay = append(outGif.Delay, 0)
}
gif.EncodeAll(w, outGif)

Is there an easy way in golang stdlib to accomplish this?

It seems an automatic way of intelligently generating palettes is missing from the golang stdlib (correct me if I'm wrong here). But there seems to be a stub for providing your own Quantizer, which led me to the gogif project. (Which was the apparent source of image.Gif.)

I was able to borrow the MedianCutQuantizer from that project, defined here:

https://github.com/andybons/gogif/blob/master/mediancut.go

Which results in the following:

var subimages []image.Image // RGBA, etc. images from somewhere else

outGif := &gif.GIF{}
for _, simage := range subimages {
  bounds := simage.Bounds()
  palettedImage := image.NewPaletted(bounds, nil)
  quantizer := gogif.MedianCutQuantizer{NumColor: 64}
  quantizer.Quantize(palettedImage, bounds, simage, image.ZP)

  // Add new frame to animated GIF
  outGif.Image = append(outGif.Image, palettedImage)
  outGif.Delay = append(outGif.Delay, 0)
}
gif.EncodeAll(w, outGif)

Instead of generating your own palette, you can also use on of the predefined (https://golang.org/pkg/image/color/palette/)

...
palettedImage := image.NewPaletted(bounds, palette.Plan9)
draw.Draw(palettedImage, palettedImage.Rect, simage, bounds.Min, draw.Over)
...