diffuse contribution vs intenstity

[Crayox13]

Hi guys,
I've only started to use diffuse contribution recently. In sun settings for instance...I didn't even test it as I was sure it only affects direct light contribution (reduces it in my case since I used 0.1 values) but leaves 1.0 intensity for the GI contribution. So I tested this just now and saw it DC affects Gi as well. The difference is that the area light by sun is a bit different but overall the room is light the same with 1/0.1 or 0.1/1 for DC/intensity values.

The thing is that I want the scene that receives GI from the sun too but no burned areas, as I saw many times asked here. I use reinhard and burn value of 0.1 here, but if I go lower I just get less saturation.

So here's a scene only light by sun
Intensity 1.0
DC 0.1


The other way around
Intensity 0.1
DC 1.0


Here's the scene with hdri sky added too. Is there a way to make the sun as on the first image but the overall light as here?


I know it's not physically correct but clients tell me all the time my walls are grey instead of white since I usually reduce exposure to reduce the burned areas.

[^Lele^]

While a bit tricky, it can be achieved, and exactly so (minus the look of the Background).
First, set up the lighting withsun, sky and a domelight to hold the sky map, all at their default contributions, but set the dome to be invisible.
Then, duplicate (copy!) the Dome Light, make a copy of the original sky map, and assign it to the new dome, set the new dome back to visible.
Proceed to set all the influences for the new dome off (all three. checkboxes).
Finally, Edit the second sky map in the material editor, set it to manual sun node, pick the original sun, and just set the sky map overall multiplier to something small (say, 0.1 or lower.).

Now you have the first dome lighting your scene physically right, while the second dome affects nothing of the lighting, but overrides the background with a dynamically reacting copy of the original sky, with lower multiplier.
Notice that since the two maps aren't an instance, changing sun direction will work for both, but changing sky parameters (ozone, turbidity, sky model, and so on) will need to be manually matched in both sky maps.

[Crayox13]

Hey,
thanks for this....but I didn't mean I have a problem with the background but the way sun hits the surface through the windows. I want my sun to contribute to the GI with its warmth but also I want it not to burn the areas it hits. At first I thought this can be achieved by lowering the diffuse contribution but then I realized that affects the GI as well....so it's almost the same as lowering its overall intensity multiplier.

[piotrus3333]

this is all default (sun plus sky in dome, highlight compression in VFB) apart from turned off vinietting, adjusted expo in camera and sun size.
generic white walls plus floor roughly resembling photo gray card. looks like yours I guess.

[stevesideas]

Instead of reducing exposure just adjust the reinhard burn values in render dialogue or the highlight burn in the VFB. Alternatively, if this is just a still, use OCIO filmic profiles and then copy/paste the image from the VFB to photoshop.

[piotrus3333]

his burn is already on 0.1

[^Lele^]

Hey,
thanks for this....but I didn't mean I have a problem with the background but the way sun hits the surface through the windows. I want my sun to contribute to the GI with its warmth but also I want it not to burn the areas it hits. At first I thought this can be achieved by lowering the diffuse contribution but then I realised that affects the GI as well....so it's almost the same as lowering its overall intensity multiplier.

I did indeed misunderstand you.
And yes, you are right, it's generally wiser to lower overall contribution when needed, rather than the component (works fine to reduce diffuse until you add a specular.).

The only way you'd have to achieve that would be through the way you do it with Reinhard, ie. with a non-linear tonal compression.
I'd very much suggest to go about it in post, with render elements and proper, selective curve tools, but any such method would work (F.e.: Reinhard with burn at 0, Exponential with bright multiplier at 0, and so on), at the expense of flattening the image look severely, and skewing the GI if the CM is baked in.

[Crayox13]

Thanks again guys. I went back and reset everything again. So, yes, default values with burn adjustment in VFB gives the best results and exactly what I wanted. Only thing is that I sometimes I render several frames in sequence so they would all be saved with the same values. That's why I thought there's a better way. How come none of the color mapping settings don't do that? I mean that burn value in VFB is just perfect! And different from what reinhard does.

Also, this cannot be done in PS right? Since shadows/highlights option is only available at 16bit (and it gives different results). I know I shouldn't use PS for this but I'm so used to it.

Oh and looking into OCIO profiles, first time I heard of those

[piotrus3333]

highlight compression is the same as reinhard burn in color mapping settings.
to move it to PS just save a cube file from VFB with full highlight compression and load it via color lookup adjustement layer. and save 32bit exrs, will not fully work with 16.

[dlparisi]

highlight compression is the same as reinhard burn in color mapping settings.
to move it to PS just save a cube file from VFB with full highlight compression and load it via color lookup adjustement layer. and save 32bit exrs, will not fully work with 16.

In Photoshop you can also embed a 32 bit smart object into either a 16 or 8 bit file. Put your put correction in the 32 bit object and you should be good to go. This has allowed me to use my standard Photoshop workflow without the limitations 32 bit sometimes imposes (no curves!).