Reflections in HDR

[Per-Anders]

Make sure you export to a 32bit file format.

[C.Smith]

Yeah, that's why I was saying I use OpenEXR and as far as I know it doesn't support anything other than 32bitfloat.

I may have answered my own question. On the reflectivity channel I set it to more than 100%. I did a separate reflection pass to 600%. Then in AE I appear to be getting a good HDR result.

[Per-Anders]

I'm unable to confirm that here, you are setting the output in the Multipass tab itself to HDR or a 32bit depth type aren't you? We're not talking about what's in the render settings "Save" tab. And whatever you're reflecting is fully HDR isn't it (and actually has correct depth after being reflected? You can check by using the picture viewere gamma/brightness control, remember that reflection is the value being reflected mutliplied by what's in the reflection channels texture and then added to the rest of the surface).

[C.Smith]

I'm not using the multipass in this case. I am doing it manual. For a reflection pass, I change it from a value that looks good in a "beauty pass" which would be 15% or so and shutting off all materials except the reflection channel and setting the reflection value not just to 100% but to 600% to 900% then rendering that pass to Open EXR at linear Gamma (1.0).

In AE, I have a 32bit float project. Then I use The Orphange's Linear ICC color profile to work in linear space.

I seem to be getting a better result, but I'm still not getting the full range. In the original HDR image I can drop the exposure to -8 and still get a crisp sun. In my render even at 900% a -8 gives me a decent sun but it's a bit dimmer. So it's still in a range separate from the clouds, but not quite what it was in the original HDR image.

[C.Smith]

Here are some results:

Original HDR image. Used in SKY object. Viewed in AE with Exposure at -8.0
http://sugarfilmproduction.com/probe.png

Here is a render from AE as OpenEXR with reflection channel set to 100%.
http://sugarfilmproduction.com/100.png

Here is a render from AE as OpenEXR with reflection channel set to 400%.
http://sugarfilmproduction.com/400.png

You'll see the HDR is killed a bit. There seems to be SOME separation from the clouds but hardly what it was on the original HDR image. I don't think this has to do with the conversion to AE, because I can view it in the C4D image viewer with it's 32bit exposure set to -8.0 and it looks the same.

Am I doing something wrong or will C4D not allow the full dynamic range of an image that a material reflects be carried to the render?

[Per-Anders]

Well, it depends if you're using a texture in your reflection or diffuse channel, or the levels used in the channels. If your original has a texture in there than it's your reflected color multiplied by that, so it will be considerably lower than the original hdr image. Cinema has no problems outputting HDR in my experience, but that doesn't mean that there might not be a bug, however without seeing your scenefile and the images involved then it's hard to diagnose what the problem is.

[C.Smith]

The material has all channels off except reflection. It's an .hdr image in the reflection channel. The same one I posted above.

[Per-Anders]

You put an HDR in the reflection channel itself? Well then it's purely dependent on whats being reflected (what's in the refleciton channel isn't what gets reflected, it's jsut controlilng how reflecive the surface is with the texture). If it's a pure white background with no shading then you will get the same colors out as you put in.

[C.Smith]

Sorry, I mispoke. The reflection channel is the only thing on. That material is on the figure primitive. The HDR image is in the luminance channel of the Sky object. As seen above I did a render with reflection channel (on the primitive) set to 100% and one (on the primitive) at 400% and the High Dynamic range has obviously been killed. You can see from the original HDR image that the sun is substantially brighter than the clouds. But when reflected, it is not much brighter if at all.

[Per-Anders]

Can you post your scene file? I am unable to recreate this here and your images are less than clear.

[C.Smith]

Strange. I had not saved my original test, so I took a few seconds to recreate it and it appears to be reflecting the full range. But see what you think:

http://sugarfilmproduction.com/TestScene.zip

[C.Smith]

Okay, figured out where I went wrong before. I forgot I had put a fresnel in the reflection channel. So in the area where the sun was on the figure, it was in the area the fresnel was lowering in intensity. So that's why the sun was closer to the exposure of the edges of the figure.

I did a test comp in AE using only diffuse passes, the reflection pass, and AO pass.

Didn't need specular passes now since the sun is so perfectly isolated from the rest. Just duplicated it, blurred, Added on top and changed the exposure to taste. Then did this again with a much larger blur. Nice result without the fake looking specular passes.

Now to get CS3, work in true linear through the whole process and use the new OpenEXR plug so I can pass in many channels in one file.

[C.Smith]

If anybody cares to see the result of my test. Here is a render out of AE. This is with no specular pass or specular channel on anywhere. The sun in the HDR image creates the specular hits itself:

http://sugarfilmproduction.com/result.png

[Per-Anders]

The Photoshop format and TIFF formats support 32bit with multiple layers without the need for plugins in Photoshop, the multipass output from C4D will produce just a single layered file as required, it takes no extra setup or render time than a single render (apart from the AO pass if you add that and don't have global AO in your scene).

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