This code splits a tileset into individual tiles. I use it for naming files and selecting specific tiles before TexturePacking them in LibGDX

TileSplitter

import javax.imageio.ImageIO
import java.awt.image.BufferedImage

int tileSize = 32
BufferedImage source = ImageIO.read(new File("fantasy-tileset.png"))
assert source

for (int x = 0; x < source.width / tileSize; x++) {
    for (int y = 0; y < source.height / tileSize; y++) {
        BufferedImage output = source.getSubimage(tileSize * x, tileSize * y, tileSize, tileSize)
        ImageIO.write(output, 'png', new File("output/${y}x${x}.png"))
    }
}