Painting HDR environment maps

[EricChadwick]

A couple good sites to check out.

http://www.debevec.org/HDRShop/
http://www.cgtechniques.com/

[Clanger]

Posm:
Thanks for that, looking through the links I've found this:
http://www.idruna.com/photogenicshdr.html

Looks like what I'm after except the price :cry:
I do have Satori Paint which is a 64bit painting program but I don't know how to get hdr out of it.

[EricChadwick]

Why not just paint the exposures as separate layers, then composite them in HDRShop (free)?

http://www.debevec.org/HDRShop/tutorial/tutorial3.html

[Clanger]

Did think of doing something like that but I've got a feeling it wouldn't work.
If I paint a dark image and an overly bright one with all the inbetweens the total colour range would still be stuck at 24bits as in each case I'd be limited to a small range.
I could have this completely wrong.

[EricChadwick]

Pardon me for saying so, but yes, you are wrong. :)

You only need >24bit once you combine the layers into an HDRI file.

HDRI photos are based on this principle, where you take several separate photos (each in 24bit) at different exposures, then combine these into a 64- or whatever-bit image.

[Clanger]

Probably didn't explain myself properly it's difficult to put in words.
Take a simple case, trying to acheive a grey scale that has more than 256 levels, which I think is the limit in Photoshop.
I do say 4 different pictures the first I go from pure white up to grey 64 second 64 to 128.......
How do I get Photoshop to paint the inbetweens when they're not available in the pallet?

[EricChadwick]

Yeah, OK I see what you're saying. There is a precision limit there. But I don't think it's much of an issue. Try a quickie test and see.

I think each exposure is an independent value range. If an HDRI uses 16 levels, the brightest 1/16th exposure in the final HDRI would use more than just 1/16th of the value range within a single 24bit non-HDRI image. Hmmm, not easy to explain.

http://athens.ict.usc.edu/HDRShop/main-pages/images/memorial3.jpg
Brightest exposure

http://athens.ict.usc.edu/HDRShop/main-pages/images/memorial5.jpg
Darkest exposure

[Mazer]

Thats a very interthing discution, for exanple some days ago I was trying Mental ray for Maya folowing some tuts, I first folowed the tut and rendered usig a real hdr pic i downloaded, then I got courious and wondered if I could do the same thing with other pics, so I took a simple sky map in jpg format, opened it in Hdrshop and saved it as a hdr pic, and... it worked!
Then I did one more experiment, I took the real hdr pic and saved-it as a simple Jpeg, then took that jpeg, opened it in hdrshop and saved-it as a hdr pic (using the default setings, I didnt even bother reading that part of the manual), well then i just replaced the maps in the original tut scene and made a test...
The resulsts are exactly the same! So I think you could do the same with any image...
I'm probably wrong, and there must be diferences, but for me it works, and I dont care if its not by the book;)

[EricChadwick]

I think you may be missing the subtle differences between a true HDRI and a normal image. When you convert from a single 24bit image to an HDRI you aren't getting any of the dynamic range. You still have the same 24bit source image. It is visible especially in reflection maps on semi-reflective surfaces, where the brightest areas of the skymap would be darkened down to see the stained glass for example.

[Clanger]

Posm:
When you said 'especially in reflections' a little light went on there, that is the best thing about HDR I have seen it in action, in a dark reflective surface I could see the trees through a window but in a perfect mirror the window was just white.
I think this could be faked in Photoshop with different images, not having all the inbetween colours probably would go unnoticed.

I'll give it a try.

[EricChadwick]

Great! I'm looking forward to seeing it.

[ceql]

I haven't really read thru the thread, but pixho has a HDRI fake tut, too!

http://www.3dluvr.com/pixho/tutorials/fakeHDRI/FakeHDRI_index.htm

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