I got past the 6-face tone mapping issue by using the raw file, and then using pfilt -1 -e X raw_foo.hdr > foo.hdr. I then used imagemagick to do mogrify foo.hdr foo.jpg to use in the VR program. However, I’ve just tested it using Greg’s trick of using a combined histogram and it works great, much better!
I found that I needed to use the raw file, because otherwise the pfilt that rad runs will change the values. This also means that I can’t rely on rad to automatically resize the image based on my QUALITY setting. I guess this means if I want a higher resolution and more antialiasing I need to set the options in rad carefully to give me an output raw file with the resolution that I need, and then resize it later with pfilt -1 -x /3 -y /3 ... for example for a high quality output.
You can view the thread here which has a link to the WebVR online viewer and my test render.
However I would like to try out using the 360 stereo cal file. Unfortunately, I don’t understand how to use it directly in rad. I’d like to use rad because it keeps the settings simple and I can easily use many CPU cores. Any pointers would be greatly appreciated!