Disassemble HDR

[Bao2]

Go to Photoshop and select the exposure you want and save a JPG, reload and change the exposure and save other JPG, reload the HDR and change the exposure and save other JPG... etc.

[Jens C. Möller]

What I want is to disassable the HDR and reassemble it again, without any loss of dynamic. Is that possible?

[richardjoly]

Hi Jens,
I am pretty sure that once pictures are combined into an HDR image, there is no reverting to the original inputs but I'm often proved wrong...

Here are some interesting reads for the math inclined and an open source app to play with HDRs.
http://www.anyhere.com/gward/papers/cic06.pdf
http://www.mathworks.com/company/newsletters/digest/2008/july/hdri.html
http://qtpfsgui.sourceforge.net/about.php

I wonder why you would want to do that...

[Jens C. Möller]

Hello Richard,

I want to do that - once again - to work around the limitation of Camera not to be able to render out HDRs. I am working on an animation of a car (what else) that drives along in a stylized environment. My shading tests have been made with an HDR environment, and I would like to use that for the animation also, since it looks very nice.

Since the HDR is a static picture that I use for illumination and reflections it will not move when the car travels along its path. So I thought I use the HDR as a texture and render out a mirror ball of the moving car and use that later as animated illumination and reflection map.

I would need to disassamble the HDR, use different exposures as textures, render out the mirror ball and recombine the mirror ball images later into HDRs again that would be used as a sequence for illumination and reflection - while I have not tested yet if EI will allow the use of image sequences as source for GI.

Thank you for the links. I will study them and see if I come any further.

Greetings

Jens

[arketype]

Hi Jens,

You should be able to "split" the HDR into LDR image files as suggested- by using photoshop and saving at different exposure levels.

Your process (in theory) should work.

I have done extensive testing with animated HDR/EXR images for lighting and it is supported in EIAS, but it is not optimum. Since each animation frame can have drastically different HDR values there tends to be a lot of "flashing" between frames.

Good Luck,

Dave

[Jens C. Möller]

Hi Dave,

yes, that is due to the HDR implementation in EIAS which automatically adjusts the exposure...

I wish we had just normal exposure controls with the EIAS to adjust the exposure. Maybe I need to use something else.

Thank you Dave.

Jens

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