jankifier/filters/posterize.go

package filters

import (
  "image"
  "image/draw"
  "image/color"
  "math"
  "github.com/disintegration/gift"
)

const (
  NoDither=0
  FloydSteinDither=1
  AtkinsonDither=2
)


type PosterizeFilter struct {
  Depth uint16
  Bins map[uint16]uint16
  DitherType int
}

func Posterize(depth uint16, dither_type int) gift.Filter {
  var i uint16
  bins := make(map[uint16]uint16)
  chunk := uint16((math.MaxUint16 + 1) / int(depth))

  // BUG: this was fine with uint8, now it's dumb as hell
  for i = 0; i < math.MaxUint16; i++ {
    bins[i] = (i / chunk) * chunk
  }

  return PosterizeFilter{depth, bins, dither_type}
}

func (filter PosterizeFilter) Bounds(src image.Rectangle) (dst_bounds image.Rectangle) {
  return src
}

func (filter PosterizeFilter) Quantize(c color.NRGBA64) (color.NRGBA64, color.NRGBA64) {

  newpixel := color.NRGBA64{
    filter.Bins[c.R],
    filter.Bins[c.G],
    filter.Bins[c.B],
    c.A,
  }

  err := color.NRGBA64{
    c.R - newpixel.R,
    c.G - newpixel.G,
    c.B - newpixel.B,
    c.A,
  }

  return newpixel, err
}

func DistError(old color.Color, quant_err color.NRGBA64, term float32) color.Color {
  dumb := old.(color.NRGBA64)

  c := color.NRGBA64{
    dumb.R + uint16(float32(quant_err.R) * term),
    dumb.G + uint16(float32(quant_err.G) * term),
    dumb.B + uint16(float32(quant_err.B) * term),
    dumb.A,
  }

  return c
}

func (filter PosterizeFilter) FloydStein(x int, y int, dst draw.Image, quant_err color.NRGBA64) {
  dst.Set(x+1, y,
    DistError(dst.At(x+1, y), quant_err, 7.0/16.0))
  dst.Set(x-1, y+1,
    DistError(dst.At(x-1, y+1), quant_err, 3.0/16.0))
  dst.Set(x, y+1,
    DistError(dst.At(x, y+1), quant_err, 5.0/16.0))
  dst.Set(x+1, y+1,
    DistError(dst.At(x+1, y+1), quant_err, 1.0/16.0))
}

func (filter PosterizeFilter) Atkinson(x int, y int, dst draw.Image, quant_err color.NRGBA64) {
  delta := [6]image.Point{
    {x+1, y+0},
    {x+2, y+0},
    {x-1, y+1},
    {x+0, y+1},
    {x+1, y+1},
    {x+0, y+2},
  }
  bounds := dst.Bounds()

  for _, d := range(delta) {
    if d.In(bounds) {
      dst.Set(d.X, d.Y, DistError(dst.At(d.X, d.Y), quant_err, 1.0/8.0))
    }
  }
}

func (filter PosterizeFilter) Draw(dst draw.Image, src image.Image, _ *gift.Options) {
  bounds := src.Bounds()

  gift.New().Draw(dst, src)

  for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
    for x := bounds.Min.X; x < bounds.Max.X; x++ {
      from := dst.At(x, y)
      c := from.(color.NRGBA64)
      newpixel, quant_err := filter.Quantize(c)

      dst.Set(x, y, newpixel)

      switch filter.DitherType {
        case FloydSteinDither:
          filter.FloydStein(x, y, dst, quant_err)
        case AtkinsonDither:
          filter.Atkinson(x, y, dst, quant_err)
      }
    }
  }
}