I have a .png image which I need to save in 24 and 16bit using gimp. I went to Image -> Mode -> Indexed, but maximum value is 256 colors. I tried to paste in 16777216 colors for 24bit, but it did revert back to 256. I also tried 16bit 65536 colors, but it also reverted back. I'm using OSX gimp version, don't know if it changes anything. I need this for school. In photoshop it's a lot easier, but unfortunately I can't use photoshop.