An 8 bit mask may be needed

[scuniff]

An 8 bit mask may be needed

https://github.com/fiji/IO/blob/1fa709937a44b369c3d56545cea191f0b0b821ed/src/main/java/sc/fiji/io/icns/IOSupport.java

Line 104:
return ((data[0] & 0xFF) << 8) + data[1];

should have an 8 bit mask & operation added:
return ((data[0] & 0xFF) << 8) + (data[1] & 0xff);

This eliminates sign extension issue.

This snippet I think exemplifies the fix:

    byte[] data = new byte[2];
    data[0] = (byte)0x80;
    data[1] = (byte)0x80;

    long incorrect = ((data[0] & 0xff) << 8)  + (data[1]);
	System.out.println("Incorrect " + String.format("0x%08X", incorrect));

	long correct = ((data[0] & 0xff) << 8)  + (data[1] & 0xff);
	System.out.println("correct " + String.format("0x%08X", correct));

Output:

Incorrect 0x00007F80
correct 0x00008080