Replica Island has variably-sized objects, stored as individual images (and
sequences of images for frames).  But we need to represent our objects as a
single tiled image.

If you have a bunch of object images of various sizes, and you want to
make a tiled image, you place one image of each object in a directory,
numbering them sequentially and putting in transparent placeholders for
unused object IDs:

  00_player.png
  01_coin.png
  02_ruby.png
  03_diary.png
  04_trans.png

You can then convert these images into a tile image using the 'convert' and
'montage' commands from ImageMagick:

  # Trim transparent borders off of images.  This is necessary to make
  # nice tiles out of characters who are 1.5 tiles high with a 2-tile high
  # image.
  mkdir trimmed
  for F in *.png; do
    convert $F -bordercolor none -border 1x1 -trim +repage trimmed/$F
  done
  cd trimmed

  # Shrink images larger than 32x32.
  mkdir shrunk
  for F in *.png; do
    convert $F -resize '32x32>' shrunk/$F
  done
  cd shrunk

  # Center images on 32x32 tiles.
  mkdir fitted
  for F in *.png; do
    convert $F -background none -gravity center -extent 32x32 fitted/$F
  done
  cd fitted

  # Assemble tiles into a single image.
  montage *.png -tile 7x -geometry +0+0 -background none objects.png
