Hi there! I'm just beginning to learn Octane, and am doing so by using the Houdini plugin version of it. I'm trying to understand some fundamental concepts, one of which is creating an image-based light. The process is confusing me, and I'm hoping someone might be able to offer me advice.
To isolate my testing, I've set up an extremely simple scene in Houdini: I have a single sphere with a chrome shader on it, and a single Environment Light. The texture of the Environment Light is a High-Dynamic Range, scene-referred linear image (i.e. an image-based light), in EXR format. I leave all light parameters on the Environment light set to their default. When I poke render in Houdini, I see this image, which is exactly what I expect:
I'm having a very difficult time replicating this in Octane. Here's what I've done (with questions included along the way)
--I create a new, empty Octane network, and create a very simple renderTarget setup consisting of the thinLens camera and the Pathtracing kernel. I *think* that by not including a camera imager node, I'm bypassing any postprocessing/LUT/molesting of final rendered pixel values:
--I create a second, empty Octane network, and create (what I think should be) a constant-shaded material:
--On the TEX_IMAGE node, I have Power and Gamma both set to 1 (QUESTION: why is the default 2.2 if we're working in linear color space?)
--On the EMIS_TEXTURE node, I have "SurfaceBrightness" ticked on, power set to 1, which I *think* should basically mean "just give me the raw pixel values of this image".
--On the MAT_DIFFUSE node, I have diffuse set to 0, which I *think* should render this a completely constant-shaded material, correct?
--I have a chrome Octane shader assigned to my chrome sphere, and I create a second sphere, 100x larger than the first, to which I assign this simple constant-shaded material. I *think* this is how the docs describe setting up an image-based light in Octane (I understand it's effectively emissive geometry).
This produces this image. You can see the Octane render (on the right) is notably darker than the Mantra render on the left. The harsh colors imply, to me, a gamma issue:
--I found an option in the Octane Options dialog to set a custom IPR gamma. I tick this on, and set the gamma to 2.2. When I rerender, I see this:
The Octane render now looks overbright (and desaturated).
Can anyone either explicitly explain how I should be going about setting this up, or point me to docs that thoroughly explain this?
Thanks so very much!