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.

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.

Lights spots on the ceiling - the best way to get rid of them, it place the land behind the window. I mean to put outside the plane near the window with a dark (the more darker the less light on ceiling) material. You can give a little color and color of light on celing will be the same.

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.

Lights spots on the ceiling - the best way to get rid of them, it place the land behind the window. I mean to put outside the plane near the window with a dark (the more darker the less light on ceiling) material. You can give a little color and color of light on celing will be the same.

For interiors desired value for ISO - 400 (less do not desirable, will be dark).
f-number - it is desirable stand between 11 and 16, and if you have pictures of a single object, making it the focus (vase in the interior, the phone on the table, etc.) then the value should be small aperture from 2 to 8 .
Shutter speed - it is the value that can be changed to select normal lighting visualization. (! but only when set the value of Film speed (ISO) and the f-number) its limits from 30 to 500, but it is possible and above or below.

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

Lights spots on the ceiling - the best way to get rid of them, it place the land behind the window. I mean to put outside the plane near the window with a dark (the more darker the less light on ceiling) material. You can give a little color and color of light on celing will be the same.

VrayLight in portal mode MUST have put on the outside of the room, and not internal, as is the normal practice. The noise will be much less. Well, and of course subdivs for portal mode (which means primary light will be either Sky or HDRI) will need two times greater than for normal VrayLight of the same size.

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.

1. Make object
2. Assign to it Vray Material
3. Choose projection type: UVW Mapping
4. Choose in Attributes Menu: Edit - > Set As Default...
5. Now all new Vray Materials will have UVW Mapping by Default.

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.

VrayLight in portal mode MUST have put on the outside of the room, and not internal, as is the normal practice. The noise will be much less. Well, and of course subdivs for portal mode (which means primary light will be either Sky or HDRI) will need two times greater than for normal VrayLight of the same size.

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

Noise is different and treated differently.
Only describe the causes of small grains (no stains!).

1. Noise directly from the light. Often, on the border of light and shadow. Particularly strong from Vraylight if there is an object. The closer the object is to VrayLight, the more noise. Increase subdivs of Light or AA settings (preferably find averages for both, not only raising a one parameter)

2. The noise in the materials (and reflect refract glossiness). It depends on the settings of glossiness subdivs in material. Treated with settings of material and AA. Again, it is desirable to gradually raise both. If speed is important of course. If not, you can use DMC AA and increase global multiplier and noise threshold.

3. Noise from highlight glossiness. And often it is not important, use you this option in the material or not. Just when it is used appears more noise. So, the noise treated with rising subdivs but only at VrayLight (NOT IN MATERIAL!) And the AA settings. Naturally you must raise subdivs in that Light from which is the noise.
(c) Saluto

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

You can customized Balance of white with "white sheet." To do this, you need to create a small white box in center of camera view. Then render its region, and pick color of it. Then put this color in the white balance physical camera.

For interiors desired value for ISO - 400 (less do not desirable, will be dark).
f-number - it is desirable stand between 11 and 16, and if you have pictures of a single object, making it the focus (vase in the interior, the phone on the table, etc.) then the value should be small aperture from 2 to 8 .
Shutter speed - it is the value that can be changed to select normal lighting visualization. (! but only when set the value of Film speed (ISO) and the f-number) its limits from 30 to 500, but it is possible and above or below.

Any pair of settings makes equal brightness. What use does not matter if you do not use the DOF. Adjust brightness using ISO settings.

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.

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.

VrayLight in portal mode MUST have put on the outside of the room, and not internal, as is the normal practice. The noise will be much less. Well, and of course subdivs for portal mode (which means primary light will be either Sky or HDRI) will need two times greater than for normal VrayLight of the same size.

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.

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