drastically different exposure with v-ray region rendering

[Tony_Morev]

Not sure if this had been reported already ...
Whenever a region is tight on a light the exposure of the whole rendered area changes. A wider region remedies the problem somewhat.
Very inconvenient when trying to preview things with region rendering. Plus i suspect it affects rendering in strips as well.

[Alex_M]

We've got the same issue too - small region renders are overexposed compared to the rest of the image.

[tashko.zashev]

This could be due to the Light cache calculations. Are you using GI with LC for this project?

[Tony_Morev]

IMap+LC
hadn't been an issue before though

[vlado]

If the region is small, the light cache doesn't get enough samples to compute the lighting levels with sufficient accuracy.

Best regards,
Vlado

[peterguthrie]

with faster computers these days, and light cache really not taking very long, could the light cache calculate the whole scene even for region rendering either as an option or by default?

[vlado]

That's the way we did it in the begining. Maybe just some clamp to a minimum value will work.

Best regrads,
Vlado

[peterguthrie]

yeah i remember the discussion back then. When region rendering (these days) I'd say I'd always want the lighting to be correct rather than the render being a few seconds quicker. Or is there some other reason other than speed?

how about a vote?

[super gnu]

on my current job, the lightcache takes 10 minutes to calculate, so it would have to be either smart, or optional.

[peterguthrie]

fair enough. would love an option though

[^Lele^]

You COULD work around the problem even now.
Only, you'd have to activate BF as primary method, so that the retrace option in the LC worked.
Further, IRMap as primary method may compound the issue, due to it being interpolated across a different set of samples, in the crop versus the full image.
I tested with BF as primary, and no matter the size of the crop, the results stay identical.