Hello!
Thanks Fred for the suggestion
I wrote down a Bash script called
trim-ratio which trims an image around the highest detail region without changing its aspect ratio.
The complications were 1) to maintain the same AR and 2) to control how much is trimmed.
I ended up manipulating the crop parameters in bash using bc, rather than in ImageMagick.
I hope this approach will make it easier in the future to improve the script.
The script requires bash with the bc library, and it is run like this:
Code: Select all
./trim-ratio.sh <input image> [<padding (default 0px)>] [<output folder (default current folder)>] [<blur (default 5px)>]
The main limitations I can think of are:
- The padding strategy is quite simple: padding is added uniformly in the four dimensions, no matter where the highest detail region is.
- I have tested the script only on square AR.
- In general, I am not an expert of IM, so I am sure there will be many ways in which the script can be impoved.
The script and a basic documentation can be found on Github => https://github.com/coccoinomane/trim-ratio.
I have included examples in the following folders:
I copy the script here for convenience, but please refer to the Github link if for the most up-to-date version:
Code: Select all
#! /usr/bin/env bash
# Trim an image around the highest detail region without
# changing its aspect ratio.
#
# Optionally specify how many pixels to pad around the
# highest detail region; the padding will be taken
# from the actual image.
#
# Useful to trim background around the subject, while
# keeping the same AR and having control on how much
# is trimmed.
#
# Requires bash with the bc arithmetical library.
#
# TODO
# * Implement different padding strategy; at the moment
# the padding is uniform in the four dimensions no matter
# where the highest detail region is.
# * Test on AR different from a square
#
# THANKS TO:
# - Fred (fmw42) and Snibgo from ImageMagick forums
# (https://imagemagick.org/discourse-server/viewtopic.php?f=1&t=36443)
# Parse arguments
image="$1"
pad=${2-0}
out_folder=${3-.}
blur=${4-5}
# Get of image info
name=$(magick "$image" -format "%t" info:)
W=$(magick "$image" -format "%[w]" info: )
H=$(magick "$image" -format "%[h]" info: )
AR=$(magick "$image" -format "%[fx:w/h]" info: )
# Output images
trimmed_image="${out_folder}/${name}_blur${blur}_trim.jpg"
padded_image="${out_folder}/${name}_blur${blur}_pad${pad}.jpg"
echo "Processing image ${name} with size ${W}x${H} and AR=${AR}..."
# Get rectangle bounding highest definition area, and store its parts
bounding_rectangle=$(magick "$image" -canny 0x1+10%+30% -blur "${blur}"x65000 -format "%@" info:)
echo " bounding rectangle = $bounding_rectangle"
WB=$(echo "$bounding_rectangle" | sed -E -e 's/^([[:digit:]]+).*/\1/')
HB=$(echo "$bounding_rectangle" | sed -E -e 's/^.*x([[:digit:]]+)\+.*/\1/')
xB=$(echo "$bounding_rectangle" | sed -E -e 's/^.*\+([[:digit:]]+)\+.*/\1/')
yB=$(echo "$bounding_rectangle" | sed -E -e 's/^.*\+([[:digit:]]+)$/\1/')
[[ $bounding_rectangle = ${WB}x${HB}+${xB}+${yB} ]] || { echo "Error extracting crop dimensions"; exit; }
# Exit if nothing can be trimmed
(( WB == W && HB == H )) && { echo "Nothing to trim, will exit"; exit; }
# Output image with bounding rectangle
magick "$image" -crop "$bounding_rectangle" +repage "$trimmed_image"
# Compute available space in the 4 directions
ST=$yB
SB=$((H-HB-ST))
SL=$xB
SR=$((W-WB-SL))
echo " available space: top=${ST}, bottom=${SB}, left=${SL}, right=${SR}"
# Initialize parameters of new crop area
WT=$WB
HT=$HB
xT=$xB
yT=$yB
# Recover aspect ratio
if (( $(echo "$WB > $AR*$HB" | bc) )); then
echo " forcing aspect ratio to $AR"
HT="$(echo "$WB/$AR" | bc)"
yT="$(echo "$yB+($HB-$HT)/2" | bc)"
echo " height changed from $HB to $HT"
echo " vertical position (y) changed from $yB to $yT"
else
echo " forcing aspect ratio to $AR"
WT="$(echo "$AR*$HT" | bc)"
xT="$(echo "$xB+($WB-$WT)/2" | bc)"
echo " width changed from $WB to $WT"
echo " horizontal position changed from $xB to $xT"
fi
# Add padding
if (( pad > 0 )); then
WT="$(echo "$WT+$pad" | bc)"
xT="$(echo "$xT-($pad)/2" | bc)"
HT="$(echo "$HT+$pad" | bc)"
yT="$(echo "$yT-($pad)/2" | bc)"
fi
# Round to integer
WT="$(echo "($WT+0.5)/1" | bc)" # round to int
HT="$(echo "($HT+0.5)/1" | bc)" # round to int
xT="$(echo "($xT+0.5)/1" | bc)" # round to int
yT="$(echo "($yT+0.5)/1" | bc)" # round to int
# Output final image
padded_rectangle="${WT}x${HT}+${xT}+${yT}"
echo " final rectangle = $padded_rectangle"
echo " writing to $padded_image"
magick "$image" -crop "$padded_rectangle" +repage "$padded_image"
Please let me know if you have any suggestion to improve the script.
Thank you,
Guido
