Some useful one-liners for Imagemagick, including resizing, convert to pencil and fake miniature

imagemagick-oneliners.bash

# Make * work in bash or zsh:
# zsh
setopt extendedglob
# bash
shopt -s extglob

# Resize all images (in-place) in a folder
# to 1200 pixels on the longest side
mogrify -resize 1200 *.jpg

# Resize and reduce quality to be better suited for a blog post.
# Usually, I don't notice a visible drop in quality,
# but I'm also not an expert :-)
convert -format jpg \
    -strip \
    -interlace plane \
    -quality 50% photo.jpg \
    -resize 1200 photo_resized.jpg

# Find the edges/outlines of a photo, not too many lines
# (canny is the name for an algorithm that finds outlines)
convert ^*canny*.jpg \
    -set filename:original %t \
    -resize 1200 \
    -canny 0x3+5%+15% \
    -negate '%[filename:original]_canny1.jpg'

# Find the edges/outlines of a photo, many lines
convert ^*canny*.jpg \
    -set filename:original %t \
    -resize 1200 \
    -canny 0x1+10%+20% \
    -negate '%[filename:original]_canny2.jpg'

# -Sketch parameter outputs pencil-like drawing.  It works very differently on
# different images. You might want to play around with removing the -negate
# parameter. It worked well for a fairly bright photo but might not for others.
# See also: https://legacy.imagemagick.org/Usage/photos/
convert photo.jpg \
    -resize 1200 \
    -colorspace gray \
    -negate \
    -sketch 0x20+120 photo_sketch.jpg

# A slightly better (at least for me it seems) version of the above is to
# create a pencil tile with motion blur and then apply it over the image
# See also: https://legacy.imagemagick.org/Usage/photos/
convert -size 256x256 \
    xc: +noise Random \
    -virtual-pixel tile \
    -motion-blur 0x20+20 \
    -charcoal 1 \
    -resize 50% pencil_tile.gif

# And then
convert photo.jpg \
    -colorspace gray \
    \( +clone -tile pencil_tile.gif -draw "color 0,0 reset" \
    +clone +swap -compose color_dodge -composite \) \
    -fx 'u*.2+v*.8' photo_sketch2.jpg

# There's also charcoal of course.
# See also: https://legacy.imagemagick.org/Usage/photos/
convert photo.jpg \
    -charcoal 1 photo_char.jpg

# Make a photo look like a miniature
convert photo.jpg -sigmoidal-contrast 10x50% \
    \( +clone -sparse-color Barycentric '0,0 black 0,%h gray80' \
    -solarize 50% -level 30%,0 -write mpr:blur_map \) \
    -compose Blur -set option:compose:args 10x0 \
    -composite mpr:blur_map \
    -compose Blur \
    -set option:compose:args 0x10 \
    -composite photo_miniature.jpg