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putyi #16679 ez folymatosan kérdés volt, íme a válasz:
The irradiance min/max settings are indeed resolution dependant (the presets are just different combinations of the irradiance map settings, min/mac, clr, nrm, dist, etc...). The prepasses are calculations of irradiance map for a lower resolution of the image, and in the following prepass it uses this info to refine the solution on a bit higher resolution image etc.
If the GI solution in a render looks good on let's say 800*600 with irradiance to -3,0 and you then change the res to 1600*1200, you can decrease the irradiance settings to -4,-1. (so -1 if you double resolution). This will give you almost exactly the same irradiance map.
Example: If you calculate irradiance map at -3,-0 for 800*600, this means the following:
prepass1: GI calculated for image with resolution 100*75 (=800/2/2/2 and 600/2/2/2)
prepass2: GI calculated for image with resolution 200*150, with the info it gathered from the first pass (=800/2/2 and 600/2/2)
prepass3: GI calculated for image with resolution 400*300, with the info it gathered from the second pass (=800/2 and 600/2)
prepass4: GI calculated for image with resolution 800*600, with the info it gathered from the third pass
Because each new pass uses the rougher info from it's previous pass, vray knows where the more important (detailed) areas are, and therefore doesn't need to calculate more samples in the less detailed (flat) areas.
So if you want the same irradiance map info for the image @ 1600*1200, use -4,-1:
prepass1: GI calculated for image with resolution 100*75 (=1600/2/2/2/2 and 1200/2/2/2/2)
prepass2: GI calculated for image with resolution 200*150, with the info it gathered from the first pass
prepass3: GI calculated for image with resolution 400*300, with the info it gathered from the second pass
prepass4: GI calculated for image with resolution 800*600, with the info it gathered from the third pass
HSph subdivs is the same as the hemispherical rays of fr, they only need lower values in vray. 50 is good for almost anything, try lower first, and if there are too many artifacts, go higher. Interp samples defines how the GI info at neighbouring samples is merged into each other. Higher values will tend to blur the solution, so the image looks smooth but looses detail (GI detail). Lower values will cause more splotches but better detail. So to get better quality, raise hsph and lower interp (but 50/20 is usually very good!)
Another important one is clr thresh and nrm (leave dist to 0.1 always). Both 0.3 is good, lower values will cause long rendertimes. Higher values speeds up things, but you loose detail again