i noticed 2 errors in image editor blender 2.78c.create new 32bit file select rgb (0.5,0.5,0.5) -fill/draw-result color is 0.2,0.2,0.2 -gamma correction should not be done for linear 32bit image.open any exr/hdr save as jpg(8bit) again result is gamma corrected i.e. 0.2 value in exr saves as 0.5 in jpg.