fly-through renders overbright

[dynaman]

maybe someone can help me out here...i'm trying to set up an exterior fly-around animation. right now i'm just in the process of running test renders using LC for primary and secondary bounces. i've got one vray sphere light as the sun, and a bunch of shadow mapped omnis (multipliers between 4 and inside the buildings. i'm using vray 1.47.
when i render single test frames with light cache subdivs set to 500, the frames render fine. but when i increase the subdivs to 3000 and set the light cache to fly-through mode, about 1/3 of the way into the calculation i get a huge list of overbright objects. the final frame renders like a green screen has been overlaid onto the render.

the problem seems to occur only when the subdivs value goes above 2000 and the shadow mapped omnis are turned ON.

any suggestions would be appreciated.

thanks.

[Da_elf]

whats the advantage of shadow maps rather than vray shadow? just shorter render time?

[dynaman]

shorter render times was the idea. it's an irregular shaped building so large planar lights wouldn't work very well. not going for hyper-realism, just something kind of flashy. omnis were the ticket back in the days of scanline.
i tried replacing the omnis with vray sphere lights. solves the overbright problem, but a single frame now takes 45 minutes to render, multiplied by 1800...well, that's just not feasible.

[Da_elf]

so you specifically need a soft shadow?

[dynaman]

i think i've got something that will work now. still using shadow mapped omnis, although fewer, with lower multiplier with a larger attenuation range.
i just don't understand why the overbright problems don't show up until you raise the lightcache subdivs above 2000.
the problem with trying to illuminate large spaces with a few vray sphere lights is that you either have to make the diameter very large, which drastically increases render times, or you end up looking like a supernova is occuring inside your building.

[Da_elf]

i think i've got something that will work now. still using shadow mapped omnis, although fewer, with lower multiplier with a larger attenuation range.
i just don't understand why the overbright problems don't show up until you raise the lightcache subdivs above 2000.
the problem with trying to illuminate large spaces with a few vray sphere lights is that you either have to make the diameter very large, which drastically increases render times, or you end up looking like a supernova is occuring inside your building.

can you show an example of how the vray sperical light is used? why not an omni with vray shadow

[dynaman]

i tried the omni / vray shadow. again, the problem is when you increase the size of the sphere dimension which produces the soft shadow, you end up with painfully long render times. i'm basically trying to fake the effect of numerous lights filling a space by using as few as possible. normally i would use a rectangular area light, but the building is a long meandering curved shape.

anyway, i'm back on track now, as i said, still using shadow mapped omnis, but just with a much larger attenuation area and lower multiplier. haven't run into any more overbright errors.
thanks for the suggestions.

[Aldaryn]

If we need to fill larger interiors with light smooth and fast, we usually put large light emitting planes, boxes etc. into the scene. This has the advantage of being very flexible, and - calculated and stored in the irradiance map - pretty fast too. There will be no direct light rays, so that will speed thing up, and you don't have to resort to shadowmaps, and omnis.
Of course the emitting geometry should be invisible to the camera, to reflections refractions, and should cast no shadows. However, it will still cast GI shadows, so you would want to keep them a bit away from flat surfaces where a sudden lightness change would look really bad.

best regards,

A.

[dynaman]

hey aldaryn - thanks for the suggestion. i may try this more often. i have used this technique in certain situations where we just need to add some brightness without detail lighting. not sure that it would have been effective in this case, but maybe worth a shot.
you mention that you make the objects visible to the camera; i wonder if it might look better if they weren't visible? would behave more like a non-visible area light? i think i'll play around with this a bit.

[Aldaryn]

Sorry, I said invisible. We usually use these light emitting geometry instead of invisible VRay lights. The size of these lights usually pretty big, so the irradiance map can sample them very well, and they can produce very clear and sharp shadows too. I don't know if Vray currently treats geometry with VRayLight shader applied differently than other geometry considering GI calculation, but in many situation we were surprised to see how fast clear, and accurate the results were considering GI shadows and the lack of splotches.

best regards,

A.

[dynaman]

sorry - my bad. skim reading too quickly.
i did go back to this scene and tried re-lighting it using light emitting geometry as you suggest. it looked OK, but overall seemed a little washed out. not a bad effect, but didn't seem as crisp as using true lights.
are there any other properties or settings that you can alter within the objects to generate more defined shadows? actually, come to think of it, we were using light cache for both primary and secondary bounces (very tight timeline and trying to gloss over detail)...maybe if i were using irradiance map for primary it would have produced crisper results. when i have a chance i'll try this again...