Any way to render multiple exposures at once?

[erickdt]

Hi All,

 

I was wondering if there was any way to render mulitple vray physical camera exposures at once to later be merged into an HDR image for post processing. Any advice would be greatly appreciated!

 

E

[kristofferhelander]

Don't you get a full HDR image if you just disable exposure and render to floating point EXR?

[erickdt]

I'm not sure. I've only ever dabbled with using EXRs. I am currently using 16 bit TIFs.

 

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[alias_marks]

I think Kristoffer is on the right track with using exr's, however I'm not sure why you would disable exposure? Care to elaborate Kristoffer?

 

If you save out a 32 bit exr, you will have much more exposure adjustment capabilities in Photoshop. i.e. bring detail back in from over blown out hot spots, etc.

[kristofferhelander]

Exposure is a form of Color Mapping, so by using it you're breaking the linearity of the image, it is no longer Gamma 1.0. So for compositing this is not good. Keep it linear and only display it in sRGB.

[Ismael]

http://www.luminous-landscape.com/tutorials/expose-right.shtml

[erickdt]

Thanks for all of your help guys. Looking into these methods now.

 

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[erickdt]

One more question: I am wondering how to make selections in this 32bit format. Over the years I have seen that most people who use this workflow use the VRay Multimatte Element to mask out objects/parts of the scene. How does one achieve this in Photoshop with a 32 bit file? There is no magic wand or select by color options. Any advice would be greatly appreciated!

 

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[Nic H]

I don't understand...you have to have exposure on in vray camera for it to act properly -it is not a form of colour mapping as far as i know...colour mapping is something that is controls the way the exposure looks. im pr

 

So do not turn off exposure - just get your image well balanced with no blowouts and then render to .exr.

 

What are you planning on doing with the 'multiple exposures' anyway?

[kristofferhelander]

Booth Color Mapping and Exposure changes the values of the pixels. So by turning them off, you get the raw light data. You can then do the Exposure in post.

Edited April 26, 2012 by kristofferhelander
spellschecking

[erickdt]

What are you planning on doing with the 'multiple exposures' anyway?

 

I was interested in messing around with HDR tone mapping to accomplish looks similar to what's seen in Claudio's photographs.

 

After finally figuring out the EXR workflow (per Kristoffer's suggestion) I've found that the 32bit full float format has alot more control and flexibility than anything I had been used to. I am currently preparing to use this workflow on an upcoming "live" project for the first time. I will not however be disabling exposure.

 

E

[andregurgel]

Maybe you can get what you want making just a small configuration on the vray frame buffer. I'm not sure but I think it works only for vray 2.0.

 

When you open the vray frame buffer you'll see a picture of a small gear ( Exposure corrections), you should click on it to enable. After that, you should click on the first button, on bottom left. You'll see a new window and in the top of it you can change de exposition, even if you have the final render. This way you can change the exposition and save the image how many times you want.

 

If you have doubts about the buttons you can check on this site -

http://www.spot3d.com/vray/help/200R1/vfb_index.html

 

I hope it helps.

Edited April 26, 2012 by andregurgel

[Nic H]

Booth Color Mapping and Exposure changes the values of the pixels. So by turning them off, you get the raw light data. You can then do the Exposure in post.

 

oh that sounds like a bizzare thing to do

how do you see the lighting you have done?

i thnk you are doing it wrong!