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View Full Version : custom decay on FG-bounces, why is it impossible?


Niber
06-16-2010, 03:37 PM
If you look at my attachment it explains how I want the FG-bounce from my spotlight to reach further, but NOT brighter!

it appears I have no choice but to use GI for this (where there is decay exponent option), but I don't understand why there can't be a global value for how fast FG decays, so that I could then turn that one down and the FG would reach further without being too bright.

I think I read somewhere (years ago) that the only way to do this is to make the entire scene smaller, but currently I've made my scene super-tiny and I'm not sure if it made it any better.

In theory if I render out the FG-pass into a 32-bit EXR and then use curves in photoshop I could make it longer, but obviously I was hoping for easier solution :)

pap87
06-16-2010, 03:50 PM
If you arent already, you should apply a gamma of 2.2 to your render whether it's via a lens shader like the mia_exposure_simple or in post, and apply a gamma of .455 to your colour textures. What that will do is keep the colours the same, but the light bounces will become much more prominent without having that burnt lighting close to the light.

TaKIKO
06-16-2010, 03:56 PM
Looks like your viewing this in linear space. Put a lens shader on it with 2.2 gamma and see how it looks. Then read about linear workflow , color spaces,etc.

Edit: Pap beat me to it

Niber
06-16-2010, 04:02 PM
hmm sounds like a strange workaround but ok I'll try it now and will report back

Niber
06-16-2010, 04:30 PM
That does indeed make FG decay a bit slower, I did however find that all lamps looked a bit desaturated and fog-falloffs looks like its falloff is not as smooth (like you might expect from tempering with curves), but if it's recommended to use gamma-correction as a rule then I guess I will use it, cheers guys.

but getting back to the topic, there's still no custom control right? (unless you wanted to use that 2.2 and 1/2.2 tweaking back and forth whenever you want FG-decay to be even longer)

coccosoids
06-16-2010, 11:35 PM
I think you need multibounces...

Niber
06-17-2010, 08:11 AM
I think you need multibounces...
eh no.. that's not the issue, the problem is not that the wall isn't in direct enough line to spotlight, the problem is simply distance.

Sorath
06-17-2010, 12:55 PM
why not cranking up the secondary diffuse scale in the fg tab.
then you get higher intensitie there.

but actually I would oldshool light that, looks way better and has more control.
and it's faster to render.

TaKIKO
06-18-2010, 03:06 AM
eh no.. that's not the issue, the problem is not that the wall isn't in direct enough line to spotlight, the problem is simply distance.


The distance isnt the problem. As said before its the way your viewing your renders. But If wanna ignore the whole linear workflow thing youll have to cheat it and use another light.

InfernalDarkness
06-20-2010, 01:34 AM
Final Gather "Scale" affects distance. This is used to overcome scene scale, without rescaling the scene.

That said, I often leave this at 1 and simply scale my scenes down by .1x/y/x, and ignore "actual measurements" inside Maya, as working from inches/feet then converting to cm/m doesn't make my lighting look any more realistic inside Maya/MR.

Scale on secondary also helps. You can push either way, way above 1 if you need your FG light to go further.

pap87
06-20-2010, 05:12 AM
Final Gather "Scale" affects distance. This is used to overcome scene scale, without rescaling the scene.

That said, I often leave this at 1 and simply scale my scenes down by .1x/y/x, and ignore "actual measurements" inside Maya, as working from inches/feet then converting to cm/m doesn't make my lighting look any more realistic inside Maya/MR.

Scale on secondary also helps. You can push either way, way above 1 if you need your FG light to go further.

Final Gather Scale is a multiplier, hence why it is a colour swatch rather than a value attribute. It can be used to strengthen, weaken or tint the final gather effect.

Niber
06-21-2010, 11:52 AM
Final Gather "Scale" affects distance. This is used to overcome scene scale, without rescaling the scene.

That said, I often leave this at 1 and simply scale my scenes down by .1x/y/x, and ignore "actual measurements" inside Maya, as working from inches/feet then converting to cm/m doesn't make my lighting look any more realistic inside Maya/MR.

Scale on secondary also helps. You can push either way, way above 1 if you need your FG light to go further.
I'm afriad you are wrong, at least me testing shows otherwise, and the help-file says:
"Primary Diffuse Scale The Scale value allows you to easily control the intensity and color of the final gather contribution on a global scene level. You can use the Color Chooser or use the slider to set the Scale value.


"

Niber
06-21-2010, 11:54 AM
why not cranking up the secondary diffuse scale in the fg tab.
then you get higher intensitie there.
Well yes that's one alternative which I will probably use,
but I still don't understand why there just isn't a FG-decay value, but ohwell maybe there is a technical reason why that's impossible or something

Sorath
06-21-2010, 12:11 PM
well the filter acts kinda like a decay - if you put it to two you would get a faster dropoff..
but since default is at 0 you can't decay wider.
maybe you will want to make the value of the light emitting finalgathering when it's current value is for example 10 - try raising to 50 and then lower the primary diffuse scale and the secondary to not blow out everything, theoretically you get more fg distribution in terms of decay.
but haven't tried that.. just an assumption.

cheers
Bastian

InfernalDarkness
06-21-2010, 10:50 PM
I'm afriad you are wrong, at least me testing shows otherwise, and the help-file says:
"Primary Diffuse Scale The Scale value allows you to easily control the intensity and color of the final gather contribution on a global scene level. You can use the Color Chooser or use the slider to set the Scale value.

Be not afraid. I was not in error. Final Gather Scale (and secondary bounce scale) both affect distance. The key is to push them past the number 1, which is the default "maximum" of the slider. But click it and you can enter any number you like.

That is, in a given scene, a FG Scale of 2 will illuminate roughly twice as far as 1, and FG Scale 4 roughly four times as far. Also, a Scale of .5 will illuminate as far as the default of 1.

I've been using this as a super-quick (but flawed: no "physical accuracy" involved with this technique) workaround when scenes are too dark or too bright since Maya 6. The results haven't changed since then.

pap87
06-23-2010, 05:28 PM
I'm afraid you should be afraid :D because while it may "look" like the distance is being affected i assure you it's not. It merely scales the effect in intensity not in distance, which of course results in more light in the scene which leads you to believe it has spread further in distance but all it has done is brighten a patch of bounce light that was almost black but not entirely black.

InfernalDarkness
06-23-2010, 08:45 PM
My fear is growing, but I shall face it head on...

You are likely correct. Perhaps the scale doesn't change the distance itself the way GI photon's exponent would, in terms of decay, but the visual result seems to have the identical effects as if it did. Like I said, this method is not remotely "accurate", but in a pinch it's been helpful for me when I need to brighten a scene at rendertime.

Niber
06-28-2010, 03:00 PM
but the visual result seems to have the identical effects as if it did.
no, sorry, it's a completely different visual effect..
Not sure how I can explain it better than what Pap already did, but basically if you make it go further by increasing the scale that means that the part nearby will be super-bright, sure there are ways to try to combat this for example by gamma of 2.2 but the point is still that you have no control over decay,

it's like in real-life, lets say the light from your LCD-monitor is lighting up your desk nicely, but if you go to your open kitchen 3m away it's too dark over there, if you could control decay (which you can't in reallife I suppose, maybe slightly be changing humidity or something) you could change the decay of the monitor-light so that it lights up the kitchen just as much as your desk,
however since you can't there's still one way you could get the monitor to light up your kitchen, by buying the worlds brigest monitor that's soo bright (i.e has the scale soo high) that it's light reaches all the way to the kitchen, but then your desk will be overly bright.
sorry best example I could come up with :P

--

But anyway to summarize the threat, I've decided that even tho my scene is mainly FG-lit, on the specific lamps where I want better control over the bounces (things like decay) I emit some GI-photons as well.
I read some really good and intresting articles on working linear-space and using 2.2 gamma in Mental Ray, but I decided against using it, cheers anyway tho it was a itnersting read.

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