HDRI Questions

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JeffBDVS
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HDRI Questions

Post by JeffBDVS » Sun Apr 15, 2012 4:29 am

After reading through the appropriate sections of the (very old) PDF manual that came with the Indigo RT installer, and then reading through the newer HTML-based manual here on the web site, I attempted to add an HDR EXR image as the light source in a test scene. My workflow:

1. Open a 4000x2000 HDR image in Photoshop
2. Resize it to 2000x2000 by letting PS squeeze the image (and not cropping it)
3. Save it out of PS as an OpenEXR file.
4. In C4D, add it to a new Indigo Material in the Emission channel.
5. Add it to the Color channel of the same material as a Texture Map, to make it easy to identify the material in the Material Manager. NB: my end result is the same whether or not the EXR image is added as a texture map.
6. Drag the modified material to the Background Material control in the Environment tab of the Indigo Renderer settings.
7. Add appropriate Indigo Materials to the other objects in the test scene and render.

Here's the result and some of my settings:
C4D-IndigoRT-HDRI.jpg
C4D Render and Settings
Questions:

For 1,2 and 3 above, is PS a proper tool to do the job of converting and resizing HDR images? Or do I need something like the Open Source Luminance HDR?

For 2 above, is it necessary to resize to make the image square? The manual says to do that, but I got the same results AFAICT using the original rectangular image.

Are there general guideline or best practices for EXR image sizes? Maybe based on the intended output, like 720x480 SD or 1280x720 HD?

Thanks,
Jeff

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CTZn
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Re: HDRI Questions

Post by CTZn » Sun Apr 15, 2012 5:21 am

Hi Jeff, I am not a c4d user but most often environment maps must be backed by a very strong emission power, try this out perhaps.
obsolete asset

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Zom-B
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Re: HDRI Questions

Post by Zom-B » Sun Apr 15, 2012 5:57 am

JeffBDVS wrote:5. Add it to the Color channel of the same material as a Texture Map, to make it easy to identify the material in the Material Manager. NB: my end result is the same whether or not the EXR image is added as a texture map.
Indigo turns each material set for Environment to a pure black diffuse with emission enabled, so no rays get reflected back from the atmo-sphere back into the scene...
You should use all your emission materials as pure black diffuse if not needed otherwise, speeds up rendering a bit :)

JeffBDVS wrote:For 1,2 and 3 above, is PS a proper tool to do the job of converting and resizing HDR images? Or do I need something like the Open Source Luminance HDR?
You can drag your HDR images into the C4D render output window, so C4D opens it. From here simply save as EXR.
JeffBDVS wrote:For 2 above, is it necessary to resize to make the image square? The manual says to do that, but I got the same results AFAICT using the original rectangular image.
No need for the resizing here! Only situation is is you use spherical envMaps, but there are quite unused nowadays...
JeffBDVS wrote:Are there general guideline or best practices for EXR image sizes? Maybe based on the intended output, like 720x480 SD or 1280x720 HD?
The bigger the more RAM indigo needs, but the sharper the BG image will be (and maybe reflections). Keep aspect ration of the image as it is, the people who did the HDRI's know best why it is that way ^^.
Regarding the lighting, there shouldn't be (much relevant) difference if your scene is lit by a 2k EnvMap or a 10k map...

I also would like to second CTZn here, try using for env maps a uniform emission of 10k-100k, its a good starting point for most scenes! Turn your tonemapping to linear or camera, and you'll see :)
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JeffBDVS
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Re: HDRI Questions

Post by JeffBDVS » Sun Apr 15, 2012 6:02 am

Thanks, guys. I'll give your excellent suggestions a try. If I can save time converting and rendering, then I'm all for that!

Jeff

JeffBDVS
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Re: HDRI Questions

Post by JeffBDVS » Sun Apr 15, 2012 8:20 am

Zom-B wrote:I also would like to second CTZn here, try using for env maps a uniform emission of 10k-100k, its a good starting point for most scenes! Turn your tonemapping to linear or camera, and you'll see :)
Where do you change those settings? In the material, I selected Use Emission Scale and Luminance, with a Value of 100000. Then I set the Indigo-tagged camera to use Linear Tonemapping. There was no difference between a Luminance value of 1000 and a Luminance value of 100000. So I figure I'm setting the wrong thing(s).

Jeff

JeffBDVS
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Re: HDRI Questions

Post by JeffBDVS » Sun Apr 15, 2012 8:23 am

NVM: I'm an idiot. The last few renders were using the C4D default camera and not the Indigo camera. When I switched to the Indigo camera, there was a huge difference!

Thanks again,
Jeff

JeffBDVS
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Re: HDRI Questions

Post by JeffBDVS » Sun Apr 15, 2012 9:51 am

Results of Emission Luminance set to 1k, 10k, and 50k when the Indigo Camera in the scene is set to Linear Tonemapping:
Attachments
HDRI_50000.jpg
HD 1280x720 Emission 50k
HDRI_10000.jpg
HD 1280x720 Emission 10k
HDRI_1000.jpg
HD 1280x720 Emission 1k

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Zom-B
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Re: HDRI Questions

Post by Zom-B » Sun Apr 15, 2012 10:22 pm

there is a close interplay between the emission (of the EnvMap) and the camera settings, the f-stop and Exposure Duration are having a big influence in the brightness of the resulting image too.
Regarding the EnvMap I was actually referring to set the "Spectrum Type" to "uniform" and the "Value" up to 10k...
I personally don't work much with the "emission scale" since it feels quite strange for me ^^

For 1 Light Scenes that all works out quite nice, since there is no interaction... combining multiple lights in a scene, of different scale and style is quite a task that needs testing. You'll end up with a "feeling" for lights, rather then pure math ;)
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JeffBDVS
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Re: HDRI Questions

Post by JeffBDVS » Sun Apr 15, 2012 11:10 pm

Zom-B wrote:Regarding the EnvMap I was actually referring to set the "Spectrum Type" to "uniform" and the "Value" up to 10k...
That's interesting, because when I set the Uniform Value to 10k and set the camera to use linear tonemapping, I get an extremely dark, almost no light image. To get a usable scene, I need at least 1M in the value *and* a Multiplier of between 100 and 200.
For 1 Light Scenes that all works out quite nice, since there is no interaction... combining multiple lights in a scene, of different scale and style is quite a task that needs testing. You'll end up with a "feeling" for lights, rather then pure math ;)
I've got a long, long way to go. As they say, "you have to walk before you can run."

Jeff

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