I just finished my implementation this morning and at the end when the color correction worked I had some issues with blur and brightness. The main ideas I got from MJPs implementation but I changed two things:
First: Sampling the luminance from the downscaled HDR texture was not acceptable for me. The average luminance difference were way too high when moving the camera through the scene. I know could change the adaption but sampling it from the whole screenspace gives smoother results too.
Second: I changed the luminance sampling code itself to the code that is provided in the DirectXSDK
I don't understand how this works. Isn't the point of downsampling so that you can get to a 1x1 texture which has the average luminance value? If you dont downsample, how do you get a single value?