caelum HDR


15-12-2008 14:13:48


I checked out the caelum HDR branch and run into some issues compiling it.
I had to add the HDRCompostior file to the project manually.
The problem now is that the HDR effect does not look like expected. Altering
the HDR parameters leads to different brightness but I can´t see any kind
of adaption or gloom. I know that this branch is not officially announced as
working/stable... so my question is when do you plan an integration
into trunk?

Thanks for work on caelum!


27-12-2008 21:20:38

That HDR branch is basically a version of HDRlib which I tried to clean-up and merge into trunk. It proved harder than I originally expected and I haven't worked on it in quite a while. There are actually several different tone-mappers inside HDRlib and the settings are very difficult to use. You CAN get pretty blooms and adaptation. Adaptation here means that it can simulate slow adaptation to abrupt screen brightness changes; not that it will automatically make the scene look "correctly". It's most definitely experimental and not usable in another project.

One problem I encountered are that some parts of Caelum are not really built for HDR (for example the sun and moon are clamped to 0-1). That can be fixed.

But what's really nasty is that you need to tweak hdr parameters for individual scenes (that's how HDRlib originally worked). You can't just throw an input image to the HDR compositor and get something appropriately light or dark. The parameters exposed by HDRlib are not particularly intuitive either so tweaking is not exactly easy. What's worse is that some shaders still contain hardcoded constants which were tweaked for the original HDRlib demo.

I want to get back to this and add more documentation and more configurable parameters; and eventually merge it into trunk. But I'm not really sure how I can get it to work nicely with a full day-night cycle (because the brighness variation is huge). It would probably require some heuristics to tweak HDRlib based on time of day/sun position.