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View Full Version : HDRI reflections cause white blowouts?



Carbon71
06-04-2003, 09:13 AM
Howdy,
I've heard many times about the realistic benefits of using HDRIs for reflections (whether backdrop or spherical map). btw- I'm talking just reflections not illumination here. They do look great, but I often get superwhite blowouts from these images (see the red circled areas in the image). I've heard solutions like, precision blur the image and use hdr expose to adjust white and black point. I've even saved a hdri out as a bmp to restrict the dynamic range that may be causing the problem (did that in my toaster image).
My question is, is there a better way? Isn't the point of using a hdri to be able to USE the high dynamic range info?!

Any suggestion are appreciated.
Carbon

Mattoo
06-04-2003, 02:03 PM
Well, it is using the HDRI info. The idea is that - that is what happens in reality, that's why you have to mess around with the exposure when printing the negative aswell as taking the picture in the real world.
Having said that, the controls in G2 are much more intuitive for controlling this kind of thing.

Dave3D
06-04-2003, 03:24 PM
u might just wana lower the brightness of the HDR map.

Carbon71
06-04-2003, 03:33 PM
yeah but lowering the broghtness takes the whole image brightness down. I wish I could just ramp down the extreme whites. I just make a .bmp of it that seems ot work fine. I just wondered what other were doing.

Omto
06-04-2003, 03:44 PM
I haven't messed with HDR much but I think you can set the maximum values for white and black through a plugin in the image editor.......I don't have LW handy at work so I can't tell you for sure.

Carbon71
06-04-2003, 03:48 PM
yeah "HDR expose" plugin let you set white and black level, but when I change the white level to get rid of those blown highlights, it still brings the overall image brightness down too much. I wish I could adjust some kind of histogram.

Elmar Moelzer
06-04-2003, 10:49 PM
Seems like your object has too strong reflections on it.
In real life you will notice that brighter things refelct more than darker ones. In LW it is the same. As a HDRI can have spots in it that are much brighter than 100% they will reflect even more.
In a well lit scene you will always have spots with more than 100% brightness. These will then show stronger in reflections.
What is the diffuse- and reflection- levels of the teapot?
You can also try blurring the HDRI a bit to get rid of some small overly bright spots.
CU
Elmar

toby
06-05-2003, 12:13 AM
btw, while I was playing with hdr I found that rendering on "enhanced" would always blow out the hotspots - kinda like crona but not as nice -