The reason the left side is so blown out is due to the fact that the image was overexposed for Jupitershine and New Horizons cameras were designed for low light at Pluto which is ideal for observing the moons of Jupiter by light reflected off their host planet. However, doing this results in the total overexposure of the side lit by the Sun.
This is another Jason Perry image and the original can be found here. Wanderingspace simply removed the lens flare noise and the overexposed color noise. He just added some New Horizons Io images that he has personally reprocessed on this page.