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// Copyright 2013 Sonia Keys.
// Licensed under MIT license. See "license" file in this source tree.
package quant
import (
"image"
"image/color"
)
// Palette is a palette of color.Colors, much like color.Palette of the
// standard library.
//
// It is defined as an interface here to allow more general implementations,
// presumably ones that maintain some data structure to achieve performance
// advantages over linear search.
type Palette interface {
Len() int
IndexNear(color.Color) int
ColorNear(color.Color) color.Color
ColorPalette() color.Palette
}
var _ Palette = LinearPalette{}
var _ Palette = TreePalette{}
// LinearPalette implements the Palette interface with color.Palette
// and has no optimizations.
type LinearPalette struct {
color.Palette
}
// IndexNear returns the palette index of the nearest palette color.
//
// It simply wraps color.Palette.Index.
func (p LinearPalette) IndexNear(c color.Color) int {
return p.Palette.Index(c)
}
// Color near returns the nearest palette color.
//
// It simply wraps color.Palette.Convert.
func (p LinearPalette) ColorNear(c color.Color) color.Color {
return p.Palette.Convert(c)
}
// ColorPalette satisfies interface Palette.
//
// It simply returns the internal color.Palette.
func (p LinearPalette) ColorPalette() color.Palette {
return p.Palette
}
func (p LinearPalette) Len() int { return len(p.Palette) }
// TreePalette implements the Palette interface with a binary tree.
//
// XNear methods run in O(log n) time for palette size.
//
// Fields are exported for access by quantizer packages. Typical use of
// TreePalette should be through methods.
type TreePalette struct {
Leaves int
Root *Node
}
func (p TreePalette) Len() int { return p.Leaves }
// Node is a TreePalette node. It is exported for access by quantizer
// packages and otherwise can be ignored for typical use of this package.
type Node struct {
Type int
// for TLeaf
Index int
Color color.RGBA64
// for TSplit
Split uint32
Low, High *Node
}
const (
TLeaf = iota
TSplitR
TSplitG
TSplitB
)
// IndexNear returns the index of the nearest palette color.
func (t TreePalette) IndexNear(c color.Color) (i int) {
if t.Root == nil {
return -1
}
t.Search(c, func(leaf *Node) { i = leaf.Index })
return
}
// ColorNear returns the nearest palette color.
func (t TreePalette) ColorNear(c color.Color) (p color.Color) {
if t.Root == nil {
return color.RGBA64{0x7fff, 0x7fff, 0x7fff, 0xfff}
}
t.Search(c, func(leaf *Node) { p = leaf.Color })
return
}
// Search searches for the given color and calls f for the node representing
// the nearest color.
func (t TreePalette) Search(c color.Color, f func(leaf *Node)) {
r, g, b, _ := c.RGBA()
var lt bool
var s func(*Node)
s = func(n *Node) {
switch n.Type {
case TLeaf:
f(n)
return
case TSplitR:
lt = r < n.Split
case TSplitG:
lt = g < n.Split
case TSplitB:
lt = b < n.Split
}
if lt {
s(n.Low)
} else {
s(n.High)
}
}
s(t.Root)
}
// ColorPalette returns a color.Palette corresponding to the TreePalette.
func (t TreePalette) ColorPalette() color.Palette {
if t.Root == nil {
return nil
}
p := make(color.Palette, 0, t.Leaves)
t.Walk(func(leaf *Node, i int) {
p = append(p, leaf.Color)
})
return p
}
// Walk walks the TreePalette calling f for each color.
func (t TreePalette) Walk(f func(leaf *Node, i int)) {
i := 0
var w func(*Node)
w = func(n *Node) {
if n.Type == TLeaf {
f(n, i)
i++
return
}
w(n.Low)
w(n.High)
}
w(t.Root)
}
func Paletted(p Palette, img image.Image) *image.Paletted {
if p.Len() > 256 {
return nil
}
b := img.Bounds()
pi := image.NewPaletted(b, p.ColorPalette())
for y := b.Min.Y; y < b.Max.Y; y++ {
for x := b.Min.X; x < b.Max.X; x++ {
pi.SetColorIndex(x, y, uint8(p.IndexNear(img.At(x, y))))
}
}
return pi
}
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