layered rendering / HDRI / camera response curves Tweet

[v-cube]

Hello octane team,

I have a few questions concerning Imager settings, exr export and render calculations, I tried to find answers in the forum but did not really succeed... I really hope you can take the time to help me here.

for fine tuning the lightning our current workflow is to tinker around with the response curve ( typically we would use agfacolor vista 800cd to get a little bit more light to darker areas...) / gamma / exposure until we are satisfied with the result and then save the as 16-bit png image.
Sometimes we also use other channels like ambient, environment+alpha and light passes or masks.
Since I struggle sometimes to get my interior renderings really bright looking without overburning or sacrificing the realistic look,I tried out the layered rendering exr output.
However, I have difficulties to archive the look I used to get with my old technique in PS. I think that I still do not 100% understand how octane handles the saving of exr files, so I would like to ask some questions to help me understand what's really going on:

1. let's say I have an Image which resembles the look I like in the octane viewport, let's assume we have the following settings in the imager :

exposure: 5, gamma: 1, response curve: agfacolor vista 800cd, highlight compression: 1. exr output is switched to tonemapped exr.

now I save this as a layered exr, which of these settings are used in the exr image export ? as far as I can tell from my initial tests, it seems to me that Exposure is used, Highlight compression is not used , gamma is not used, camera response curve is not used.

The funny thing thing that I do not understand is, that when I open some of the exr images with different camera response curves in PS , they resembles somehow (not 100% thought...) the look of my octane viewport when I am using my trusty old vista 800cd curve...
Is this a coincidence ? I do not really understand this ... And is it possible to enable a camera response curve in octane, that will simulate the look of the exr file opened in PS? And also the other way around, is there a way to apply a curve (or whatever...) in PS that would make the image look like your octane viewport with a certain camera response curve applied? How can I archive the octane viewport appearance in PS?

2. I am a little bit unsure, If I understand the way octane is calculating the rendering, especially in conjunction with the adaptive sampling...
I always thought , that everything you do in the octane Imager tab is somehow "post render" and therefore you can change values in real time without the need to re-render something. If this is true, is it so that when you adjust things to brighten up your image like changing gamma or applying camera response curves, this will lead to more prominent noise in darker areas, since kernel settings like "path termination power" are energy based? So you would basically make an area, of the image which octane regards as so dark that it does not need more samples, brighter and therefore expose the noise which is a result of fewer samples...
This should be also true for the adaptive sampling: although you can dial in "expected exposure" which is probably? used to help the algorithm to tell if an area containing noise is relevant or not , applying a camera response curve will alter the brightness of certain areas. An Image with camera response curve A will show more noise than the same Image with camera response curve B when A is boosting darker areas. In my Imagination octane will probably do the calculations with a internal gamma value of 1, the gamma 1 image is therefore the basis for things like path termination or the noise threshold... is this correct?

If this is true, wouldn't it make sense to have an option for a second calculation mode, which would adapt to the users Imager settings like gamma, camera response curve and maybe also exposure , by distributing the calculation power to the intended image and not the internal Image?

I hope I was able to express myself, english is not my mother tongue and the subject is rather complex for me, so excuse me for any wrong spelling.

thank you for any feedback

best

Andreas

[v-cube]

Ok, I was able to save a tonemapped exr file, opened it in PS and applied a gamma of 0,45 ( 1 divided by 2,2 ) the image resembles the look of the octane render viewport, in this special case I used : Exposure :1.1 , Highlight compression :1 , camera response curve : Ektachrome64TCD , Gamma: 1.1

So when saving as single layered tonemapped exr I am able to mimic the octane viewport look in PS. However if I use the "save layered exr" button in the octane viewport, the resulting file does not seem to be tonemapped (I am using the octane for Rhino plugin by the way...) when importing the tonemapped exr in PS the image looks kind of washes out, which is then fixed by applying gamma 0,45 as mentioned above, the layered exr on the other hand looks like it is saved as a regular exr , which i cannot turn into something like the octane viewport...

attached 2 Images, one is a screendump of the octane render viewport, the second is the imported tonemapped exr image with an gamma of 0,45 applied :

as you can see, the files look the same (apart from the bloom glare effect I forgot to turn off...)

Is there a way to save the layered exr tonemapped ? Or is this nonsense since the composting in PS will not work properly?

looking forward to some comments...

best

Andreas