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HDRR problem with image key

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Fighting with this one since weeks now. I'm using the enhanced reinhard operator which by itself seems to work more or less ( I'm still fighting though with bright areas due to specular reflection to be white and not dim ). The problem is now the calculation of the image key. For testing purpose I simply down sampled the image using a simple average shader down to a 1x1 ( multiple renders ). This I can then feed in the tone map shader to render. Of course this is a yet-to-now approach but for enough for testing. There are now a couple of problems I can't wrap my head around. 1) Lit Room ( 3 point lights ): Looking around the room the key changes noticeable especially if you look at the window into the darkness outside. The dark outside cranks down the image key and things get glaring. 2) Dark corridor with a lit room at the end: Image key is very low due to massive amount of dark pixels so the room is a glaring white blob. The averaging has the problem that dark areas quickly pull down the image key resulting in overexposure. For the first example the image key should be rather steady since in the real world the eye doesn't have to adjust itself while residing in a room even if you peek out of the window into the night. And in the second case you can also ( in RL ) see well the lit room and the corridor is just dark. In this case the image key should be matching the room and not the larger quantity of dark corridor. Looking at the averaging way of obtaining the image key I see no way to get this done correctly. I thought about using an 8x8 grid or larger over the image and calculate individual image keys for the grid cells ( which afterwards produce a seamless transition due to GL_LINEAR ) so bright areas and dark areas can exist next to each other. But then it could happen that dark areas in a lit room aure suddenly dodged which is wrong too. Any ideas on how this problem can be solved? How do others tackle this image key problem? Just averaging or image keys for sub sections? I'm new to this HDRR stuff and no matter how much I search around the net the tutorials and information papers always lack this "little info" which is required to give sense to the whole beast.

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