d.backgroundIndex = d.tmp[11]
		// readColorTable overwrites the contents of d.tmp, but that's OK.
		if d.globalColorTable, err = d.readColorTable(fields); err != nil {
			return err
		}
	}
	// d.tmp[12] is the Pixel Aspect Ratio, which is ignored.
	return nil
}

func (d *decoder) readColorTable(fields byte) (color.Palette, error) {
	n := 1 << (1 + uint(fields&fColorTableBitsMask))