Image to braille (without dithering)

image_to_braille.nim

import std / [os, unicode]
import pkg / pixie

const Root = currentSourcePath().parentDir

var im = readImage(Root / "bird512.png")
im = im.resize(80, 80)
im = im.resize(im.width - (im.width mod 2), im.height - (im.height mod 4))

const start = 0x2800 # "⠀" base braille char codepoint

proc getBlackWhite(px: ColorRGBX): int =
  return ord((0.299 * float(px.r) + 0.587 * float(px.g) + 0.114 * float(px.b)) * (float(px.a) / float(uint8.high)) > 0.5)


template getChar(a, b, c, d, e, f, g, h: ColorRGBX): Rune =
  (
    Rune(start + getBlackWhite(a) +
                 (getBlackWhite(b) shl 1) +
                 (getBlackWhite(c) shl 2) +
                 (getBlackWhite(d) shl 3) +
                 (getBlackWhite(e) shl 4) +
                 (getBlackWhite(f) shl 5) +
                 (getBlackWhite(g) shl 6) +
                 (getBlackWhite(h) shl 7))
  )

template gpx(im: Image, x, y: int): ColorRGBX =
  im.data[y * im.width + x]

var output: string

for y in countup(0, im.width - 4, 4):
  # var y = y * 4
  for x in countup(0, im.height - 2, 2):
    # var x = x * 2
    output.add(getChar(im.gpx(x, y), im.gpx(x, y+1), im.gpx(x, y+2), im.gpx(x+1, y), im.gpx(x+1, y+2), im.gpx(x+1, y+3), im.gpx(x, y+3), im.gpx(x+1, y+3)))
  output.add('\n')

var f = open(Root / "output.txt", fmWrite)
f.write(output)
f.close()