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Thread: Rendering to HDR

  1. #1
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    Default Rendering to HDR

    Speaking of tonemapping, I wasn't quite getting the sort of exposure I was looking for from the options in IRay so I thought I would try Photoshop, but the renders don't seem to have much color depth when saved as EXR or 32-bit TIFF, I can't retrieve any detail from the blown-out areas in Photoshop...testing if I can brighten up a darker image better now. What should my workflow be? This is for a lighting design project, I'm trying to match some very subtle effects from prototypes.

  2. #2
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    If you want to do the tone-mapping externally then you would need to disable the internal tone-mapper, unchecking it in the rendering settings should do the trick.

  3. #3
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    So I did that, with the light brightness set according to the light specs, but as I said the result didn't seem to have much extra color info to actually work with in Photoshop.

  4. #4
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    I am not able to reproduce this issue. With tone-mapping off I save out a .exr of a spotlight against a plane, bright enough to white out a large portion of it without tone-mapping. Here is is in Photoshop with exposure at 0:

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    And here it is if I reduce the exposure:

    Click image for larger version. 

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    If the HDR data wasn't there then the entire white region would simply go a darker grey when reducing the exposure rather than revealing the detail.

  5. #5
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    But I don't seem to have as many stops of exposure to play with as in-render...would that be fair to say. I can't seem to save out an HDR of any old scene with tonemapping off, which makes it render out pure white as a rule, and get the detail back in PS.

  6. #6
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    I'm not really sure I understand your question. If you are saying you don't have as many stops to play with in Photoshop, that's down to Photoshop. If you mean that you can get better adjustment using the actual tone-mapper that isn't surprising because Photoshop isn't doing anything sophisticated when you just change exposure. When using the exposure control in the renderer you are doing a more sophisticated tone-mapping. Photoshop does have other options for tone-mapping besides exposure though (as do other programs).

    If you have tone-mapping off then all of the information is preserved so you have the full range to work with, whether the software you choose to manipulate it makes good advantage of that is up to the software and not anything we can influence.

  7. #7
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    Well thought I would revive this thread since it's more relevant than my title about "volumetrics."

    I don't know what's in the scope of you guys to give advice on, but I got a plugin for HDR processing in After Effects that can do bloom and glare. Great, wonderful, but now that I'm running it through that I seem to have to start over on the scene exposure--and this is common to any of my attempts to do anything with HDRs--I bring it in and it looks nothing like the iRay render, which...well is to say the least a bit cumbersome. How do people do this? What simple thing am I missing?

  8. #8
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    Basically you're doing the tone-mapping outside Iray and After Effects will have different tone mapping methods so it will definitely look different. Some people actually prefer to do their tone-mapping outside Iray because they don't like the built in one, however it can be challenging to replicate the look of the built in one since that isn't available in external tools.

    In some cases, you can leave the tone-mapping on and set the gamma to 1.0 to get linear output (still output to .hdr) and then still fudge some of these effects in tools like After Effects, however it won't have the same strong highlights to drive the glare.

    I'm definitely not an expert at After Effects tone-mapping and post effects, so perhaps someone else where has some ideas on that.

  9. #9
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    Thanks Paul...probably really dumb question here, but...if I use the tonemapping in Iray...the output isn't going to be HDR?

  10. #10
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    Yes, that is correct, however if you use a gamma of 1.0 and still output to a .hdr there will be more information than if you output to a regular 8-bit image, but yes, it won't have the full dynamic range. It does give post tools more room to fudge than regular images. However for true HDR output you'll need to turn off the tone-mapper.

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