I double the LDR brightness with the HSV value set to 2. In some sense, now, this image is HDR since it (potentially) has pixel values in it greater than 1. But its only a ruse. The truly bright data is still missing. I just amplified the remaining data to compensate a little.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)