OTOY Forums

Hi there;

I'm working through (re)learning Octane after many years, and something's confusing me I can't quite figure out. I'm rendering a scene with a very bright visible light source, but when I inspect the light's pixel values in Mplay's IPR render view, the values all seem to be clipped just under 1. How can I render/view true, untonemapped pixel values?

Sorry, what Octane for Houdini plugin version are you using? I think that the IPR always works in LDR mode, although of course, the final rendering to disk or to MPlay is done in full HDR. I ask about the version because there are a lot of changes in the IPR rendering in the latest Octane 2020.2 builds, including the processing of the IPR in HDR mode.

Thanks,
-Juanjo

Hey Juanjo;

I'm using a version I just purchased/downloaded today:
Octane_2020.2.0.4_Houdini_18.5.408_vr_Win64

Should it be possible for me to see over-range values in Mplay for IPR renders with this version? If not, is there, um, a non-IPR version of the render I could see in Houdini (much as Redshift has the IPR and "for-realsies" render modes)?

And, a follow-up question: I can't quite figure out the right incantation of gamma adjustments to allow me to view renders in Mplay in the proper gamma space. Looking through the myriad of places I can find to adjust this, I have:

On my RenderTarget node:
--Imager->Gamma = 1
--Imager->Response Curve = Linear/Off (I set this because I would like to render a linear image, with no LUT/tonemapping/anything else)
--Houdini Color Settings panel-> Gamma = 2.2 (setting this to 1 only seems to affect Houdini's viewport, which is definitely not what I want)
--Mplay preferences: Display Options-> Default Display Gamma: 2.2 (I can set gamma manually to 2.2 in the Mplay window, and things look fine, but *something* is causing this parameter to periodically set itself to 1)

Any advice?

Currently, if there is no OCIO config the IPR always works in sRGB color space mode, so this is why the MPlay gamma is set to 1.0 to avoid the double gamma correction. For the final render to disk the ROP node color space option is used, so if you configure it to linear, you should get a linear non clipped .exr file and MPlay preview, as you can see in the attached image.

Perhaps it could be a good idea to use this same parameter also for the IPR. I'll think about it.

Thanks,
-Juanjo

Thanks Juanjo!

It might be helpful to more clearly stress the importance of OCIO in Octane's installation docs (it doesn't "come by default" with Houdini, and not having it installed triggers confusing warnings and elicits confusing behavior vis a vis this gamma confusion. It also *may* be triggering crashes, as noted in other threads in this forum (I experienced these sporadic crashes, and installing OCIO seemed to fix this problem, though I'd like to be careful about implying causality there). Installing it and using the nuke-default config.ocio gives me some behavior in mplay which is much more intuitive.

I'd suggest, however, that the inability to see over-range values when rendering in IPR is pretty problematic. Having to do a batch render (and, therefore, wait for the frame to complete) to be able to view true pixel values seems needlessly complicated and confusing.

In the next plugin build, the IPR color space mode will be configured from the "Color space" Octane ROP parameter, to match the render to disk and to allow non clipped IPR preview in MPlay.

Hope it helps,
-Juanjo