I don't think you can. I'm assuming you mean 16-bit per color, or 48-bpp, right? I'm pretty sure that the Gimp's internal color precision is only 24-bit, so it's probably dithering down to that when ...

GIMP’s latest updates and long-standing input settings make it a powerful tool for artists using tablets and styluses. From configuring pen pressure to customizing brush dynamics, you can create a ...