Thanks to GEGL, our new image processing library, GIMP now supports manipulation of pixels with 16, 32 or 64 bit depth per color channel precision, both integer and float. This greatly reduces the loss of colors which occurs at 8bit precision to the rounding of color values and improves the rendering of gradients.
You will find the precision switch in the Image menu. Whenever you load an image that was saved in higher bit depth precision (see File Formats section below), GIMP automatically switches to the relevant mode.