This is a simple converter that takes in a 80x16 texture, reading first two 16x16 sprites as full-frame and no-frame, and constructs the rest of sprites for Fusion Minecraft mod sprite.

FusionPieceTexture.java

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;

public class FusionPieceTexture
{
	public static void main(String[] args)
	{
		File[] dir = new File(args[0])
				.listFiles(f -> f.isFile() && !f.isHidden() && f.getName().endsWith(".png"));
		
		if(dir == null)
		{
			System.out.println("Folder " + args[0] + " does not exist.");
			return;
		}
		
		for(File file : dir)
		{
			try
			{
				System.out.println("process " + file);
				var img = ImageIO.read(file);
				process(img);
				ImageIO.write(img, "png", file);
			} catch(Throwable e)
			{
				e.printStackTrace();
			}
		}
	}
	
	static final Color TRANSPARENT = new Color(0, 0, 0, 0);
	
	private static void process(BufferedImage img)
	{
		var gfx = img.createGraphics();
		{
			gfx.setBackground(TRANSPARENT);
			gfx.translate(32, 0);
			gfx.clearRect(0, 0, 48, 16);
			
			var noBorder = img.getSubimage(16, 0, 16, 16);
			
			// Vertical slide
			gfx.drawImage(noBorder, 0, 0, null);
			gfx.drawImage(img.getSubimage(0, 0, 1, 16), 0, 0, null);
			gfx.drawImage(img.getSubimage(15, 0, 1, 16), 15, 0, null);
			
			// Horizontal slide
			gfx.translate(16, 0);
			gfx.drawImage(noBorder, 0, 0, null);
			gfx.drawImage(img.getSubimage(0, 0, 16, 1), 0, 0, null);
			gfx.drawImage(img.getSubimage(0, 15, 16, 1), 0, 15, null);
			
			// Corners
			gfx.translate(16, 0);
			gfx.drawImage(noBorder, 0, 0, null);
			gfx.drawImage(img.getSubimage(0, 0, 1, 1), 0, 0, null);
			gfx.drawImage(img.getSubimage(15, 0, 1, 1), 15, 0, null);
			gfx.drawImage(img.getSubimage(15, 15, 1, 1), 15, 15, null);
			gfx.drawImage(img.getSubimage(0, 15, 1, 1), 0, 15, null);
		}
		gfx.dispose();
	}
}