The speed/quality can be adjusted using only 4 parameters:

1. noise threshold in DMC
2. global subdivs mult
3. subdivs at LC (in new VrayC4D it`s can be auto adjusted too)
4. resolution
The rest is not necessarily touch. Auto changes. This applies to all settings Ir map and DMC GI.

And yet! Use DMC AA 1/4. No Fixed!

(c) Saluto

Turn on in your GI reflective caustics often adds only problems. But there is a bypass maneuver, which offered a caustic little bit with a small (about 30%) increase render time but without any stains! To do this, check DE (Detail Enhancement), and to calculate the LC and Ir map in to file with switched off reflective caustics, and before render turn on casuistic and use from file LC and Ir map. Settings of DE will be responsible for the quality of caustics. For a large resolution could be left default value. For the smaller resolution it`s possible to use world and set the desired radius mm. 30-40 mm. quite enough, and fairly quickly.

Let's say the RGB value is xr, xg, xb which range from 0 to 255.

The solution:

1) Render the scene in any way you want with any settings you want, but make sure you use Linear color mapping with 1.0 for both Bright and Dark multipliers and the "Clamp output" option is off, and you are using the Vray camera "Exposure" setting. It would also be handy if you render to the Vray VFB.

2) Measure the RGB value at the pixel you need to match. If the values are, let's say (pr, pg, pb) again from 0 to 255, adjust the Vray camera "White balance" to be (pr*255/xr, pg*255/xg, pb*255/xb) and multiply the camera ISO setting by (xr+xg+xb)/(pr+pg+pb).

Note that this works only for Linear color mapping. In principle it can be done for any color mapping, but the numbers are hard to find by hand.

Best regards,
Vlado

Turn on in your GI reflective caustics often adds only problems. But there is a bypass maneuver, which offered a caustic little bit with a small (about 30%) increase render time but without any stains! To do this, check DE (Detail Enhancement), and to calculate the LC and Ir map in to file with switched off reflective caustics, and before render turn on casuistic and use from file LC and Ir map. Settings of DE will be responsible for the quality of caustics. For a large resolution could be left default value. For the smaller resolution it`s possible to use world and set the desired radius mm. 30-40 mm. quite enough, and fairly quickly.

For quick Exterior preview rendering, you need to put Vray Light in a mode Dome Area Light type and put in to Texture Sky (image, hdr or shader). Other settings are not necessarily touch. In this case, no need to include the GI, and you can see quite quickly lighting and materials. This is how it will turn out, and render final. But! Will be noisy and not very fast. And most importantly - too deep shadows. Making a contrasting picture easily. We should only reduce the gamma in color mapping.

Use light cache for glossy rays is great way to reduce render time, but sometimes we have artefacts with it.

There is simple way to avoid it, it is to turn Off prefilter and On Filter Fixed in Light Cache Reconstruction_parameters with value if Filter Size 2-3 times bigger then Samples Size of Light cache.