Frame buffer overexposure - how to use?

[baumgore]

I've got here problems changing the exposure after rendering inside the VR frame buffer. The color-space seams to be still 24 bit, white is clamped on 255, i could not get white, washed out regions to show deteils when toning down. Shouldn't it behave like an 48 bit /floating HDRI image with an endless luma-space?
How do I do it ?????