How add custom dither filter with paletted image

[diantanjung]

I implemented gift.Filter interface with method Draw below. But the result plain is white image only. Is there something wrong with my code? Or How to implement gift.Filter in the right way?

func (f ditherFilter) Draw(dst draw.Image, src image.Image, options *gift.Options) {
	dst = image.NewPaletted(src.Bounds(), color.Palette{color.Black, color.White})
	draw.FloydSteinberg.Draw(dst, src.Bounds(), src, image.ZP)
}

reference: https://golang.org/pkg/image/draw/

Thanks.