Vray Tips

[Tong]

Just some tips from some people, wit respect to Saluto and Vlado specially :wink:

1.
http://img501.imageshack.us/img501/2648/settingshg1.jpg
Any pair of settings makes equal brightness. What use does not matter if you do not use the DOF. Adjust brightness using ISO settings.

2. 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.

3. 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. (c) Saluto

4. 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.(c) Saluto

5.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.
http://img379.imageshack.us/img379/6311/lightportalct0.th.jpg (http://img379.imageshack.us/img379/6311/lightportalct0.jpg) http://img379.imageshack.us/img379/3012/lightportaldarkplanetr6.th.jpg (http://img379.imageshack.us/img379/3012/lightportaldarkplanetr6.jpg)
_____no plane____________with plane_____
(c) Saluto

6. 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.
(c) Saluto

7. 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.
(c) Saluto

[Rich_Art]

Thanks tong... very useful information...


Peace,
Rich_Art. :wink:

[scanmead]

*bookmarked* This page is going to get a lot of use!

[Tong]

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

----
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

[Tong]

The formula that V-Ray uses for the camera exposure is this (the attenuation value in the code below):

Code:
// Take f-number and focal length into account;
// based on ISO 12232:2006(E) standard for measuring ISO
// of electronic sensors (defines the ISO number in respect
// to the amount of light necessary for producing a unit
// response in the sensor)

aperture_dist=focal_length*focus_distance/(-focal_length+focus_distance);
R=focus_distance/aperture_dist;
A_eff=((R+1.0f)/R)*f_number;

attenuation=(65.0f/(78.0f*100.0f))/(A_eff*A_eff);

// Take into account the tone operator exposure
attenuation=attenuation/pi();
ToneOperatorInterface* toneOpInt=
static_cast<ToneOperatorInterface>(GetCOREInterface(TONE_OPERATOR_INTERFACE));
if (!toneOpInt) attenuation=attenuation*1500.0f;
else {
ToneOperator *toneOp=toneOpInt->GetToneOperator();
if (!toneOp) attenuation=attenuation*1500.0f;
else attenuation=attenuation*toneOp->GetPhysicalUnit(t);
}

// Take the shutter speed into account
attenuation=attenuation/shutter_speed;

// Adjust the exposure according to the user specified ISO
attenuation=attenuation*f_ISO;

Best regards, Vlado

[Tong]

In nature, hilights are simply reflections of light sources. In computer graphics, there are two ways to calculate this same effect: the one is to make no distinction between lights and other objects, and to just do reflections (what Morbid refers to as indirect hilight); the other is treat lights separately from all other objects, since they tend to be bright and their reflections are important for the appearance of the object and so it makes sense to calculate their reflections separately (what Morbid refers to as specular hilight).

It is important to realize that both methods produce the same visual results, they are just different approaches to the same effect. However, in certain situations the first method performs better, in other situations - the second. By "better" here I mean the amount of noise in the area light's reflection for a given number of samples.

Luckily, it is possible to combine (blend) both of these methods to produce a result with the least amount of noise for the given number of samples. In this case, the final result in the image is a sum of two components - one computed as a regular reflection, and the other - computed as a hilight. When added together, these produce the final accurate result. Of course, this only works correctly if both the reflection and the hilight are computed with the same glossiness value.

For artistic and render speed reasons however, V-Ray allows you to use a different glossiness for each of these effects. This is not physically accurate, but may be useful in many situations.

For car paint specifically, the correct way to do it is to use a VRayBlendMtl material to overlay several materials with different glossiness values.

Best regards,
Vlado

[Tong]

The problem:

We want to obtain an exact RGB value for some (small) surface in our image. 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 V-Ray camera "Exposure" setting. It would also be handy if you render to the V-Ray 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 V-Ray 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

[Garban]

Hi Tong!
First sorry for my english is very poor and I hope you understand me.
I have some questions about this thread:

• You show a table with pairs of F number and Shutterspeed. I dont know nothing about profesional photography and I suposse that (for example) shutterspeed= 1/125 mean SS=125 in the physical camera. Its true?

• The second question:In the table the pair is between FStop and Shutterspeed, but in the second point you set ISO value about 400 and after you say:
«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».
And if you set a pair of the table (FNumber/shutterspeed) you cant change the shutterspeed « to select normal lighting visualization». I think is Contradictory.
My second question is: If there is a metod, what is the order to set the Physical Camera value?
FNumber---Shuter Speed---Film ISO
FNumber---Film ISO---Shuter Speed

Thaks for your time and I hope understand my poor english!

[Tong]

shutterspeed= 1/125 mean SS=125 in the physical camera. Its true?
true


but in the second point you set ISO value about 400 and after you say
different aproach, quick for interiors

[Garban]

Hi Tong!
And what its the best? or depend

[Tong]

no best solution ;-)

first approach more correct from photographer view, you know we not doing images like it looks in real life, we do it like it was shot on camera. :roll:

[machmirdenlukas]

thanks tong!

[Garban]

Thanks Tong!
I will have more questions tomorrow :-)

[Tong]

Here are the forumlas for these color mapping modes:

Exponential:
Code:

float k=clamp(color.intensity(), 0.0f, 1.0f);
k=darkMult*(1.0f-k)+brightMult*k;
res=color;
res.clampMin();
res.set(1.0f-expf(-res.r*k), 1.0f-expf(-res.g*k), 1.0f-expf(-res.b*k));

HSV exponential:
Code:

float k=clamp(color.intensity(), 0.0f, 1.0f);
k=darkMult*(1.0f-k)+brightMult*k;
res=color;
res.clampMin();
float h, s, v;
RGBtoHSV(res, h, s, v);
v=1.0f-expf(-v*k);
res=HSVtoRGB(h, s, v);

Intensity exponential:
Code:

float k=clamp(color.intensity(), 0.0f, 1.0f);
k=darkMult*(1.0f-k)+brightMult*k;
float c=color.intensity();
float m=(1.0f-expf(-c*k))/c;
res=color*m;

Reinhard:
Code:

res=color*multiplier;
res=res*(Color(1.0f, 1.0f, 1.0f)+res*VR::sqr(burnValue))/(Color(1.0f, 1.0f, 1.0f)+res);


Best regards,
Vlado

[Tong]

Light Cache subdivs "optimus prime" ;-)

sqrt(H*W)*1.3=subdivs

Example:
sqrt(1024*768)*1.3=1150 subdivs

[djmag]

*bookmarked* This page is going to get a lot of use!

[vesale]

The problem:

We want to obtain an exact RGB value for some (small) surface in our image. 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 V-Ray camera "Exposure" setting. It would also be handy if you render to the V-Ray 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 V-Ray 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

hi just to be sure to understand the manipualtion, lets say that

i've got a basic color to match

Xr 255 Xg 255 Xb 255

on the render i obtain on my sample

Pr 200 Xg 200 Pb 200

so does that mean that i must do that math
(Xr 255 + Xg 255 + Xb 255=765) divided by ( Pr 200+Pg 200+Pb 200=600 )

765 divided by600 equals 1.275
so to get the correct color i must multiply my current iso, lets say 100 asa , by 1,275 to obtain a 127.5 iso result wich should correct the difference?

is that it? if so, wouldnt it be wise to use a win basic palette or mac basic palette rendered in the scene to get an average color on a grid to compare and so use the average result to up the iso?

second, that optimus prime LC cache SubD of yours, could you simplify the formula for a non math person like me? :)

thanks a lot for all the enlightment

cheers

[MrElusive]

that LC optimus forumale works in cinema 4d so no need to simplify.

In your LC subdibs value box just type in "sqrt(1280*1024)*1.3". When you hit enter, it will calculate it and give 1488

[vesale]

ok,

at least, simplifying would maybe had explain the relations between samples and aspect ratio/number of pixel relation

but, hey :) thanks :)

[Psilo]

It would also be handy if you render to the V-Ray VFB.

It sure would, but the manual says absolutely nothing about VFB. How do you render to the VRAY VFB?

[Tong]

we don`t have it, it`s unstable in c4d

[Tong]

http://img405.imageshack.us/img405/5756/littletutorialrn7.jpg

[Tong]

set the GI settings "show calculation phase" to off for LC and IR, and you can render any size up to 16000x 16000 pixels:-)

turning that off uses a lot less ram, and also renders at almots 200% speed for big images. so i recommend having this all time off for final rpint images.

we render regularly all in ca. A3 300dpi ( 5370px wide), this goes fast and nice in vray.
no need to split, just do the above.

cheers
stefan

p.s we will some time also add the vray frame buffer as option, with it you will be able to render even bigger than 16000px wide:-)

[3dkobi]

Where did this thread was hiding ......

Thanks Tong


Peace,
Kobi

[Antimatter]

haha ... Never thought about that! Just hide the prepass calculation for a render speedup. :D

Thank you for that hint :)

[VMG]

Hi tong.
Can you place the table that was here? What had the values ​​of ISO, Shutter Speed ​​and F.stop. I missed to save to me.

Thanks