Show an image in the terminal

imgcat.go

package main

import (
	"fmt"
	"github.com/nfnt/resize"
	"image"
	"image/color"
	_ "image/gif"
	_ "image/jpeg"
	_ "image/png"
	"log"
	"math"
	"os"
	"syscall"
	"unsafe"
)

func terminalSize() (w, h int, err error) {
	var sizes [4]uint16

	_, _, errno := syscall.Syscall6(syscall.SYS_IOCTL, 1, uintptr(syscall.TIOCGWINSZ), uintptr(unsafe.Pointer(&sizes)), 0, 0, 0)
	if errno != 0 {
		return -1, -1, errno
	}

	return int(sizes[1]), int(sizes[0]), nil
}

func distanceColor(ca, cb []uint32) float64 {
	return math.Sqrt(math.Pow((float64(ca[0])-float64(cb[0])), 2) + math.Pow((float64(ca[1])-float64(cb[1])), 2) + math.Pow((float64(ca[2])-float64(cb[2])), 2))
}

func idxColor(clr color.Color) int {
	var d, distance float64
	var idx int = 0
	ca := []uint32{0, 0, 0}
	table := [][]uint32{
		{0, 0, 0},
		{32768, 0, 0},
		{0, 32768, 0},
		{32768, 32768, 0},
		{0, 0, 32768},
		{32768, 0, 32768},
		{0, 32768, 32768},
		{49152, 49152, 49152},
		{32768, 32768, 32768},
		{65280, 0, 0},
		{0, 65280, 0},
		{65280, 65280, 0},
		{0, 0, 65280},
		{65280, 0, 65280},
		{0, 65280, 65280},
		{65280, 65280, 65280},
		{0, 0, 0},
		{0, 0, 24320},
		{0, 0, 34560},
		{0, 0, 44800},
		{0, 0, 57088},
		{0, 0, 65280},
		{0, 24320, 0},
		{0, 24320, 24320},
		{0, 24320, 34560},
		{0, 24320, 44800},
		{0, 24320, 57088},
		{0, 24320, 65280},
		{0, 34560, 0},
		{0, 34560, 24320},
		{0, 34560, 34560},
		{0, 34560, 44800},
		{0, 34560, 57088},
		{0, 34560, 65280},
		{0, 44800, 0},
		{0, 44800, 24320},
		{0, 44800, 34560},
		{0, 44800, 44800},
		{0, 44800, 57088},
		{0, 44800, 65280},
		{0, 57088, 0},
		{0, 57088, 24320},
		{0, 57088, 34560},
		{0, 57088, 44800},
		{0, 57088, 57088},
		{0, 57088, 65280},
		{0, 65280, 0},
		{0, 65280, 24320},
		{0, 65280, 34560},
		{0, 65280, 44800},
		{0, 65280, 57088},
		{0, 65280, 65280},
		{24320, 0, 0},
		{24320, 0, 24320},
		{24320, 0, 34560},
		{24320, 0, 44800},
		{24320, 0, 57088},
		{24320, 0, 65280},
		{24320, 24320, 0},
		{24320, 24320, 24320},
		{24320, 24320, 34560},
		{24320, 24320, 44800},
		{24320, 24320, 57088},
		{24320, 24320, 65280},
		{24320, 34560, 0},
		{24320, 34560, 24320},
		{24320, 34560, 34560},
		{24320, 34560, 44800},
		{24320, 34560, 57088},
		{24320, 34560, 65280},
		{24320, 44800, 0},
		{24320, 44800, 24320},
		{24320, 44800, 34560},
		{24320, 44800, 44800},
		{24320, 44800, 57088},
		{24320, 44800, 65280},
		{24320, 57088, 0},
		{24320, 57088, 24320},
		{24320, 57088, 34560},
		{24320, 57088, 44800},
		{24320, 57088, 57088},
		{24320, 57088, 65280},
		{24320, 65280, 0},
		{24320, 65280, 24320},
		{24320, 65280, 34560},
		{24320, 65280, 44800},
		{24320, 65280, 57088},
		{24320, 65280, 65280},
		{34560, 0, 0},
		{34560, 0, 24320},
		{34560, 0, 34560},
		{34560, 0, 44800},
		{34560, 0, 57088},
		{34560, 0, 65280},
		{34560, 24320, 0},
		{34560, 24320, 24320},
		{34560, 24320, 34560},
		{34560, 24320, 44800},
		{34560, 24320, 57088},
		{34560, 24320, 65280},
		{34560, 34560, 0},
		{34560, 34560, 24320},
		{34560, 34560, 34560},
		{34560, 34560, 44800},
		{34560, 34560, 57088},
		{34560, 34560, 65280},
		{34560, 44800, 0},
		{34560, 44800, 24320},
		{34560, 44800, 34560},
		{34560, 44800, 44800},
		{34560, 44800, 57088},
		{34560, 44800, 65280},
		{34560, 57088, 0},
		{34560, 57088, 24320},
		{34560, 57088, 34560},
		{34560, 57088, 44800},
		{34560, 57088, 57088},
		{34560, 57088, 65280},
		{34560, 65280, 0},
		{34560, 65280, 24320},
		{34560, 65280, 34560},
		{34560, 65280, 44800},
		{34560, 65280, 57088},
		{34560, 65280, 65280},
		{44800, 0, 0},
		{44800, 0, 24320},
		{44800, 0, 34560},
		{44800, 0, 44800},
		{44800, 0, 57088},
		{44800, 0, 65280},
		{44800, 24320, 0},
		{44800, 24320, 24320},
		{44800, 24320, 34560},
		{44800, 24320, 44800},
		{44800, 24320, 57088},
		{44800, 24320, 65280},
		{44800, 34560, 0},
		{44800, 34560, 24320},
		{44800, 34560, 34560},
		{44800, 34560, 44800},
		{44800, 34560, 57088},
		{44800, 34560, 65280},
		{44800, 44800, 0},
		{44800, 44800, 24320},
		{44800, 44800, 34560},
		{44800, 44800, 44800},
		{44800, 44800, 57088},
		{44800, 44800, 65280},
		{44800, 57088, 0},
		{44800, 57088, 24320},
		{44800, 57088, 34560},
		{44800, 57088, 44800},
		{44800, 57088, 57088},
		{44800, 57088, 65280},
		{44800, 65280, 0},
		{44800, 65280, 24320},
		{44800, 65280, 34560},
		{44800, 65280, 44800},
		{44800, 65280, 57088},
		{44800, 65280, 65280},
		{57088, 0, 0},
		{57088, 0, 24320},
		{57088, 0, 34560},
		{57088, 0, 44800},
		{57088, 0, 57088},
		{57088, 0, 65280},
		{57088, 24320, 0},
		{57088, 24320, 24320},
		{57088, 24320, 34560},
		{57088, 24320, 44800},
		{57088, 24320, 57088},
		{57088, 24320, 65280},
		{57088, 34560, 0},
		{57088, 34560, 24320},
		{57088, 34560, 34560},
		{57088, 34560, 44800},
		{57088, 34560, 57088},
		{57088, 34560, 65280},
		{57088, 44800, 0},
		{57088, 44800, 24320},
		{57088, 44800, 34560},
		{57088, 44800, 44800},
		{57088, 44800, 57088},
		{57088, 44800, 65280},
		{57088, 57088, 0},
		{57088, 57088, 24320},
		{57088, 57088, 34560},
		{57088, 57088, 44800},
		{57088, 57088, 57088},
		{57088, 57088, 65280},
		{57088, 65280, 0},
		{57088, 65280, 24320},
		{57088, 65280, 34560},
		{57088, 65280, 44800},
		{57088, 65280, 57088},
		{57088, 65280, 65280},
		{65280, 0, 0},
		{65280, 0, 24320},
		{65280, 0, 34560},
		{65280, 0, 44800},
		{65280, 0, 57088},
		{65280, 0, 65280},
		{65280, 24320, 0},
		{65280, 24320, 24320},
		{65280, 24320, 34560},
		{65280, 24320, 44800},
		{65280, 24320, 57088},
		{65280, 24320, 65280},
		{65280, 34560, 0},
		{65280, 34560, 24320},
		{65280, 34560, 34560},
		{65280, 34560, 44800},
		{65280, 34560, 57088},
		{65280, 34560, 65280},
		{65280, 44800, 0},
		{65280, 44800, 24320},
		{65280, 44800, 34560},
		{65280, 44800, 44800},
		{65280, 44800, 57088},
		{65280, 44800, 65280},
		{65280, 57088, 0},
		{65280, 57088, 24320},
		{65280, 57088, 34560},
		{65280, 57088, 44800},
		{65280, 57088, 57088},
		{65280, 57088, 65280},
		{65280, 65280, 0},
		{65280, 65280, 24320},
		{65280, 65280, 34560},
		{65280, 65280, 44800},
		{65280, 65280, 57088},
		{65280, 65280, 65280},
		{2048, 2048, 2048},
		{4608, 4608, 4608},
		{7168, 7168, 7168},
		{9728, 9728, 9728},
		{12288, 12288, 12288},
		{14848, 14848, 14848},
		{17408, 17408, 17408},
		{19968, 19968, 19968},
		{22528, 22528, 22528},
		{24576, 24576, 24576},
		{26112, 26112, 26112},
		{30208, 30208, 30208},
		{32768, 32768, 32768},
		{35328, 35328, 35328},
		{37888, 37888, 37888},
		{40448, 40448, 40448},
		{43008, 43008, 43008},
		{45568, 45568, 45568},
		{48128, 48128, 48128},
		{50688, 50688, 50688},
		{53248, 53248, 53248},
		{55808, 55808, 55808},
		{58368, 58368, 58368},
		{60928, 60928, 60928},
	}

	r, g, b, _ := clr.RGBA()
	ca[0] = r
	ca[1] = g
	ca[2] = b

	for i, cb := range table {
		if i < 16 {
			// We skip the first 16, because those are user configured
		} else if i == 16 {
			distance = distanceColor(ca, cb)
			idx = i
		} else {
			d = distanceColor(ca, cb)
			if d < distance {
				distance = d
				idx = i
			}
		}
	}

	return idx
}

func imgCat(img image.Image) {
	var idx1, idx2 int
	bounds := img.Bounds()

	for y := bounds.Min.Y; y < bounds.Max.Y; y += 2 {
		for x := bounds.Min.X; x < bounds.Max.X; x++ {
			idx1 = idxColor(img.At(x, y))
			idx2 = idxColor(img.At(x, y+1))
			fmt.Printf("\x1b[38;5;%dm\x1b[48;5;%dm▀\x1b[00m", idx1, idx2)
		}
		fmt.Println("")
	}
}

func main() {
	if len(os.Args) < 2 {
		fmt.Printf("Usage: %s filename\n", os.Args[0])
		os.Exit(2)
	}

	file, err := os.Open(os.Args[1])
	if err != nil {
		log.Fatal(err)
	}

	img, _, err := image.Decode(file)
	if err != nil {
		log.Fatal(err)
	}

	tw, th, err := terminalSize()
	if err != nil {
		log.Fatal(err)
	}

	imgResized := resize.Thumbnail(uint(tw), uint(th*2), img, resize.Lanczos3)

	imgCat(imgResized)
}