Download link: http://www.seenax.com/portfolio/cpp.php
I found a way to bake HDR information in one RGB image (without using any alpha channel)!!! This is a very useful technique for baking HDR lightmaps.
I used Y = 0.2126 R + 0.7152 G + 0.0722 B
function to get luminance out of an image.
In-shader computation to reverse the process
I hope it's useful,