Shrink image, longest side 576 px, either side is ajusted to multiple of 64 px (for img2img)

adjust_image.sh

#!/bin/bash
## Usage: adjust_image image.png
## => image.png will be shrinked.
## Require ImageMagick commands (convert, identify)
adjust_image() {
  local imgpath="$1"
  local outpath="$1"
  longest_side=576
  convert "$imgpath" -resize "$longest_side>" "$outpath"
  read -r _width _height <<<"$(identify -format "%w %h" "$outpath")"
  if (( _width % 64 > 0 ));then
    (( _width = ( _width - ( _width % 64 ) ) ))
  fi
  if (( _height % 64 > 0 ));then
    (( _height = ( _height - ( _height % 64 ) ) ))
  fi
  convert "$outpath" -gravity center -crop ${_width}x${_height}+0+0 "$outpath"
}