Golang pretty prime image generator, example output: http://imgur.com/w2BXltB

pi_img.go

package main

import (
	"flag"
	"image"
	"image/color"
	"image/png"
	"log"
	"math"
	"os"
)

type PiImage struct {
	x, y int
}

func (p PiImage) ColorModel() color.Model {
	return color.RGBAModel
}

func (p PiImage) Bounds() image.Rectangle {
	return image.Rect(0, 0, p.x, p.y)
}

func (p PiImage) At(x, y int) color.Color {
	n := (p.x * y) + x
	if isPrime(n) {
		return color.RGBA{colorize(x, p.x), colorize(y, p.y), 255, 255}
	}
	return color.Black
}

var picX, picY int
var filename string

func init() {
	flag.IntVar(&picX, "x", 1024, "picture width")
	flag.IntVar(&picY, "y", 768, "picture height")
	flag.StringVar(&filename, "f", "prime.png", "output filename")
}

func main() {
	flag.Parse()
	img := PiImage{picX, picY}
	file, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE, 0755)
	if err != nil {
		log.Fatalln("Failed to open", filename, " for writing:", err)
	}
	if err := png.Encode(file, img); err != nil {
		log.Fatalln("Failed to write image:", err)
	}
}

func isPrime(n int) bool {
	sqrt := int(math.Sqrt(float64(n)))
	for i := 2; i <= sqrt; i++ {
		if n%i == 0 {
			return false
		}
	}
	return true
}

func colorize(value, space int) uint8 {
	return uint8((float32(value) / float32(space)) * 255)
}