Halftone, Imagemagick

#!/bin/bash

# halftone

set -e

convert "$1" -level 0x70% \
-set option:distort:viewport '%wx%h+0+0' \
-colorspace CMYK -separate null: \
\( -size 2x2 xc: \( +clone -negate \) \
+append \( +clone -negate \) -append \) \
-virtual-pixel tile -filter gaussian \
\( +clone -distort SRT 60 \) +swap \
\( +clone -distort SRT 30 \) +swap \
\( +clone -distort SRT 45 \) +swap \
\( +clone -distort SRT 0 \)  +swap +delete \
-compose Overlay -layers composite \
-set colorspace CMYK -combine -colorspace RGB \
out_cmyk_halftone.png