A Few Questions on Rendering Exteriors

[shushens]

Hello guys! I have some questions on rendering exteriors, which have been bothering me for a while now. I will try to write them down here, short and precise:

1, In Max, you can operate with sun and sky separately. You can use a simple skylight which you can attach the HDR environment to. If I want a similar result in XSI, in which the sky controls the HDRI and sun works together with it, what is the workflow for that? I just delete the PhysicalSky and bring in an Environment, which seems kinda lame.

2, When I use Environment Blur and plug the Environment shader to its environment port, even if I do have my background slider set to 0 in the environment node, the background still shows in the render and makes all alpha channels worthless. I could not fix this problem anyhow. How does one get around to it? I selected current pass from explorer, opened render tree, attached Environment Blur to its environment shader stack and attached Environment shader to its environment port.

3, When I am using Photographic Exposure Control instead of Simple Tone Mapping, how do I get a happy setting for both the sun and the HDRI? In many many tutorials and exercise files, I have seen Max/Maya users not to touch that sun intensity 1 at all. Sometimes they lower it a bit, like 0.85 and use Photographic Exposure Control to balance the intensity. Naturally, that cuts off the HDRI completely, because its contribution is too weak. Raising exposure for the HDRI to make it show again creates odd artefacts. So, In Max, there is an unitless white balance, which you set to a very high value. For some reason (which is beyond my wits) that works well with both the sun and the HDRI. So, what is the deal here with XSI? Here I can't specify the white balance in Kelvin. I tried to attach a mia_cie_d node to the white balance and thus feeding Kelvin value, but no matter what value I feed, it's always showing up white.

4, In the linear workflow, you need to leave all the modifier maps (bump, displacement, reflection) and HDRIs to linear, and gamma correct the diffuse textures by either setting the mode to sRGB or manually setting a gamma somewhere between 1.8 and 2.2. So, now that gamma correction is already in place, when I use Simple Tone Mapping, or Photographic Exposure Control, what gamma should I put in there? PEC has default gamma 1, and STM has default gamma 2.2. They are not equivalent, are they?

5, If you manually lower the sun intensity too low, like 0.015 or something for a sunny day, and then change the 8 bit diffuse textures to sRGB, the render will look very badly oversaturated and darkened out even if you do apply on-screen gamma correction. But, if I do this by keeping sun intensity to 1 and setting cd/m^2 to something like 3000 in Photographic Exposure Control, things look pretty good and well lit. But, once again, that makes the HDRI lighting useless.

Any insight on these matters would be greatly appreciated.

[origin]

1 - sky controls hdri bitmap ? you either light your scene with skylight which is simply an automaticaly generated procedural sky OR a hdri bitmap. I don't see how 'skylight' could control the bitmap.

if you want to for example mix 'clouds' hdri bitmap with physical sky, just use mix2 plugged into env shader stack.

2- yep it shows, don't know why. Try connecting nodes like this, as far as i remember it works: environment->mia_environment_blur->environment->env shader stack, with last environment background set to 0, rest to 1.

or use mip_rayswitch_environment.

3- check out physical sky in manual. also afaik physical sun created with pass-init sky shader creates sun with soft_light shader, which should be replaced by you with physical_sun

4- setting the gamma in pec/stm to something diffrent than 1 will get your gamma burned to image. I always leave it to 1, and render to exr then apply gamma 2,2 in post.

[shushens]

Sorry, I think I phrased it wrong. Skylight doesn't control the bitmap. The bitmap controls the skylight and since sun takes after the skylight unless manually controlled, I do not have to manually adjust the colour of the sun. That way, probably things would look more in place? Just trying to guess. So just deleting the PhysicalSky shader and putting an Environment shader in there is the way to go?

If I use mix2colors, and the two colours to mix are the HDRI and the PhysicalSky, what will be the weight? I actually do something different. I plug the HDRI to the haze of the PhysicalSky. That works pretty well for me.

Using that approach took away the background Yeah now I wonder why I never thought of Environment Switcher before.

The PhysicalSun I am addressing here is how it is after replacement. Otherwise there would be no question of setting it to 0.015 for a sunny day, man.

So, should I keep HDRI and greyscale masks to linear and diffuse textures to sRGB? Or should I not even do that and accept the automatic, which makes everything linear? I keep hearing that if I take out EXR for tone mapping it outside, then I don't need to worry about colour profiles inside the 3D app. But vieweing it with LUT set to 2.2 is not really tone mapping, is it? It is just a gamma override. I always stay confused about this.

Last but not least, thanks a lot for responding. Things can sometimes get very frustrating when I have nobody to discuss it with.