jjroland opened this issue on May 08, 2007 · 212 posts
bagginsbill posted Fri, 20 February 2009 at 10:50 AM
Quote - aha now i understand. for true realistic renders we need to use HDR maps. but we can not use this for backgrounds. because this is all data.
correct?
Didn't say that. You went too far. I said it is not fair to say it is darker. Because the raw data is there, I can make it darker or lighter or anything I want, because all the true luminence is there, regardless of how super bright it is or how super dark the details are. They are all there. A true HDRI image records the actual luminence even if the brightest is a trillion times brighter than the darkest.
Ordinary JPEG, PNG, etc. do not have that kind of range. They are encoded in a narrow range. Any luminance info that doesn't fit in that range is simply discarded.
Think of the HDR image as being real life. You can take a photo of it at any number of different exposure values and display that as a JPEG. But no single JPEG can accurately depict all the values that are there.
If you're standing in an enclosed room, looking through a doorway at a brightly lit exterior, you can look at that as a JPEG with either the inside looking good or the outside looking good, but not both at the same time. This is not the same as saying you can't look at it. You can look directly at it. But first you must decide which range of values you want to map to your 8-bit illuminance range for your computer screen. That's all.
The full data is there in an HDRI, just as it was in real life, and so when we render an image that utilizes multiple exposure values simultaneously, such as looking directly at it as well as looking at muted reflections, we see detail in both as well as lost information in both.
The direct view of the doorway shows the interior wall clearly and the yard outside is totally white. The indirect view using a muted reflection on the ball shows the outside yard clearly and the interior reflection is totally black (not visible).
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)