Efficient way of OpenEXR to 8bit format with gamma encoding by OpenEXR and numpy?

Question

I'm looking for more efficient solution of converting .exr to 8bit JPEG with gamma encoding. Currently, I make use of OpenEXR module and numpy. Here is the code snippets:

File = OpenEXR.InputFile(exrfile)
PixType = Imath.PixelType(Imath.PixelType.FLOAT)
DW = File.header()['dataWindow']
Size = (DW.max.x - DW.min.x + 1, DW.max.y - DW.min.y + 1)

rgb = [numpy.fromstring(File.channel(c, PixType), dtype=numpy.float32) for c in 'RGB']
for i in range(3):
    rgb[i] = numpy.where(rgb[i]<=0.0031308,
            (rgb[i]*12.92)*255.0,
            (1.055*(rgb[i]**(1.0/2.4))-0.055) * 255.0)

rgb8 = [Image.fromstring("F", Size, c.tostring()).convert("L") for c in rgb]
#rgb8 = [Image.fromarray(c.astype(int)) for c in rgb]
Image.merge("RGB", rgb8).save(jpgfile, "JPEG", quality=95)

I'm wondering if there is even efficient solution for that?