Program creates a voronoi diagram using random sites, then colors in each site with the average color of all of the pixels contained in the site. https://blog.victor.computer/article/3

imagerandvoronoi.go

package main

import (
	"math/rand"
	"image/draw"
	"image/png"
	"image/color"
	"strconv"
	"os"
	"time"
)

func genSites(width, height int) ([][]int) {
	rand.Seed(time.Now().Unix())
	l, err := strconv.Atoi(os.Args[len(os.Args)-2])
	if err != nil {
		panic(err)
	}
	sites := make([][]int, l)
	for i := range sites {
		sites[i] = make([]int, 2)
		sites[i][0] = rand.Intn(width)
		sites[i][1] = rand.Intn(height)
	}
	return sites
}

func main() {
	inputF, err := os.Open(os.Args[len(os.Args)-3])
	if err != nil {
		panic(err)
	}
	defer inputF.Close()

	inputR, err := png.Decode(inputF)
	if err != nil {
		panic(err)
	}
	input := inputR.(draw.Image)
	minx, miny := input.Bounds().Min.X, input.Bounds().Min.Y
	maxx, maxy := input.Bounds().Max.X-1, input.Bounds().Max.Y-1
	sites := genSites(maxx-minx, maxy-miny)
	siteColors := make([][]color.Color, len(sites))
	//todo: figure out something better than this
	for i := range siteColors {
		siteColors[i] = make([]color.Color, 0, (maxx-minx)*(maxy-miny))
	}
	siteBelongs := make([][]int, maxx - minx)
	for x := range siteBelongs {
		siteBelongs[x] = make([]int, maxy - miny)
		for y := range siteBelongs[x] {
			dmin := (maxx-minx)*(maxx-minx) + (maxy-miny)*(maxy-miny)
			var smin int
			for i, s := range sites {
				d := (s[0]-x)*(s[0]-x) + (s[1]-y)*(s[1]-y)
				if d < dmin {
					smin = i
					dmin = d
				}
			}
			siteBelongs[x][y] = smin
			siteColors[smin] = append(siteColors[smin], input.At(x+minx, y+miny))
		}
	}
	siteAvgColors := make([]color.Color, len(sites))
	for i := range siteAvgColors {
		if len(siteColors[i]) == 0 {
			siteAvgColors[i] = color.RGBA{0, 0, 0, 0}
		} else {
			var sR, sG, sB, sA int = 0, 0, 0, 0
			for _, val := range siteColors[i] {
				r, g, b, a := val.RGBA()
				sR += int(r)/255
				sG += int(g)/255
				sB += int(b)/255
				sA += int(a)
			}
			//siteAvgColors[i] = siteColors[i][0]
			siteAvgColors[i] = color.RGBA{
				uint8(sR/len(siteColors[i])),
				uint8(sG/len(siteColors[i])),
				uint8(sB/len(siteColors[i])),
				uint8(sA/len(siteColors[i]))}
		}
	}
	for x := range siteBelongs {
		for y := range siteBelongs[x] {
			input.Set(minx + x, miny + y, siteAvgColors[siteBelongs[x][y]])
		}
	}
	output, err := os.Create(os.Args[len(os.Args)-1])
	if err != nil {
		panic(err)
	}
	defer output.Close()
	err = png.Encode(output, input)
	if err != nil {
		panic(err)
	}
}