MentalRay help

[mohamedberry]

hey guys, i'm still trying to improve my renderings, have read many about MR in many forums, still cant get the result i want...

 

i think i need to know what each button & value represents (and that doesnt mean i need numbers, just what it do and how) in MR rollout, like how to set the perfect photons numb. & when to proceed to final gathering, and how to get sharp shadows using raytraced shadows & MR indirect illumination, and how to increase my object's colore bleed, and how to use more than one light in the scene with out having a burned areas, and when using FG sometimes i get strange shadows at the intersecting areas of two objects and other times i get light leakage (what causes that although i'm sure the model is well closed) !!!

 

here is my settings (i use generic units& international light units), tell my if there is something to do

[aflack]

I've been using Mental Ray for about 6 months now and I find it incredibly difficult to get a really good internal image in Mental Ray, I don't have any problems with external views.

 

In-fact I hate to say it but after six months I am pretty close to giving up with mental Ray at least for internal views. The way I understood it was that you didn't need to mess with the sizes of the photons for GI and FG because MR automatically picked the best sizes. But I could be wrong!

[Ras]

Hi guys

 

I´ve been introducing a new Viz 2005 and mental ray class at the School of Architecture in Copenhagen...

 

In my experience mr is quite complex but once you get a good workflow it is very fast and understandable. I will make a little resume of what I consider an appropriate method when rendering with Mental Ray - Anyone with different approaches are welcome to pitch in. I am sitting at an old Compaq Armade E500 and I have no image references here but I´ll put them in when I have acces to them before the end of the week.

 

...

 

First of all - Use Area Lights!

 

For interior shots I always place mrAreaSpots over the window openings to simulate skylights. Ajust the Area so that it covers the entire opening and place it very close to the opening. Use an spot-angle close to 180 degrees.

Remeber - you can only see the actual area when dragging the spinners next to the Local Area Light parameters.

 

The Skylight that comes with Viz does not cast photons and therefore will not affect lighting in the scene unless Final Gather is turned on. Usually I try to avoid using FG because it is view dependent - meaning that it has to be recalculated every time you move the camera. It also has a tendency to flatten some of the nice colorbleeding effects of the photons.

I also use a mrAreaSpot as my sun. Just place it far enough away and ajust the mrAreaLight Parameters. This gives your shadow edges an increasing softness corresponding to the distance from the shadow casting edge. using shadow maps creates an allround soft edge from start to finish and using raytraced shadows gives you an allround sharp edges - arealights on the other hand will make a very believeable edge (http://www.cgarchitect.com/vb/showthread.php?t=7964)

 

Secondly - Choose your views and adjust the hotspot of your lights to fit this (these) views. Don´t change them or you will have to adjust you lighting situation again.

 

When using GI in mr you depend on the photons shot from you light source. If your hotspot is to big you will be casting photons into areas that will not affect your rendering - this means that you will need to increase the number og photons in the scene and thus increasing the rendertime.

Narrow your hotspot as much as possible and keep your rendertimes low allowing you to increase the bunber of photons in the scene.

 

Thirdly - use a neutral grey material in the material overide slot of the Processing section of the Render Window.

 

Fourthly - Consider this equation

 

X * Y * Z = NP

 

Meaning :

Local GI settings for Main lightsource (X) * Local GI settings for support lights (Y) * Global GI settings (Z) = Nice picture(NP)

...

 

 

 

This is an equation with four unknown variables and it is impossible to solve - nevertheless this is exactly our goal. In order for us to do this we must isolate one variable and make the others constant.

 

Right - first step is to remove the Y variable temporarily from the equation - this means - turn of your support lights.

 

next thing to do is to define NP according to this situation. What would a nice picture of this scene look like WITHOUT the support lights (typically the skylight = diffuse light source) - this is something you use your imagination to do - what it means is get at good idea of what you want to end up with.

 

You lock this picture in you mind as a constant - this is you goal and its "value" will not change untill we turn on the Y again - meaning that it is a constant. Lets for arguments sake say that NP=10

 

Now our equation looks like this:

 

X * Z = 10

 

Much better but still not good enough. What we will do now is to make the X constant and thus directly controlable by the Z value. Specifically this means that you set the Local Energy = 1 and photon count = 1. Now you don´t touch these parameters again!

(Generally the multiplier for the sun works well at 1.0 - But this is really only periferally relevant to this discussion as the multiplier only controls the brightness of any areas hit by direct light - for secondary arealights a multiplier of 0.25 works well in most cases in my experience)

 

For arguments sake we can say that the equation looks like this

 

1 * Z = 10

 

This means that we only have one variable to tweak. In this case it is of course Z = 10 but as this is an abstract we must adjust the global GI energy and Photon count in the rendermenu. Do this untill you definition of NP is reached.

 

How to adjust these parameters? What you do now is that you enter a photon evalutation phase. What we want to do now is to make the photons small and clear enough to estimate the number of photons and their energy.

 

This means that you set the parameter "Maximum num. of Photons per Sample" to something like 1. When I teach I call this parameter the "Splat" or "Blend" effect (Viz is a little different in this area but it is still right).

Next you set "Maximum Sample Radius" to a size that is about 1:10 of what is in your viewport - meaning that it is small but still covers a little surface. Mental Ray automatically sets the radius to something like 1/10 of the entire scene meaning that if you render a teacup on a table in a model containing a whole city your photons will be much to big. You need to control this parameter manually - for now set it to a small portion of the viewport as mentioned above.

 

With these settings you render the view until you have a (- this is really a question of learning how to recognize the signs. I am at home with my wifes laptop and i haven´t got any reference shots here but I´ll post some tomorrow)

 

Right - so now you have a nice picture with the correct globale GI settings. We will lock those down to a variable too and introduce the supportlight (Y)again. What we will also have to do is reevaluate our definition of NP since we are introducing another light source to the scene. Lets say that NP is now = 20

 

The equation:

 

1 * Y * 10 = 20

 

Y is of course = 2 - but again this is an abstract. What we have now is a set of constants X, Z and NP and a variable Y. We will tweak this locally since we have already locked the global GI parameters ("Average GI Photons per Light" and "Global Energy Multiplier")

 

Now tweak the local GI parameters of your support light untill you reach your desired NP image quality.

 

Leave Decay at 2 and other parameters like Trace Depth at the default value untill you get a good feel for the things mentioned above.

[mohamedberry]

Ras... i dont know what to say, but realy i am thankful for your help here, but i still have some check boxes & values that i dont know what it does, and i dont have much time to test every single option.

i gtg now, will but the quistions tomorrow.

 

Many thanx Ras

[mohamedberry]

For interior shots I always place mrAreaSpots over the window openings to simulate skylights.

 

well Ras... i dont like using unnecessary light sources as it'll increase the render time, and i dont like using spots specially to simulate skylite, i use one directional light insted because the directional looks better on the big scale models. and then use as few as possible of spots insede the scene to give me the light inside and to give some realism (useing the spots locations on the architectural plan)... i've been into faking radiosity and i got a conclusion that i use a spot on every openning to fake sun light, but i guess the good thing about using a GI pluging that you dont need to do all that fake stuff, just put your light as it would be in the real world (one outside as the sun, and spots insede as your real spots) and then adjust your settings to get a good rendering...

 

this is my idea about MRay & any other pluging... only the names & methods will be different but in the end, same purpose

 

about your theory, i find it very useful to teach in schools, but will fail to use it in real world, but i am thankful for your time writing all these words down

 

back to my problem... as i mentioned, i use one directional light outside the scene and use MRay shadows (or raytraced if i have windows), the thing is when i add more interior lights i got burned hot spots, and many indirect illumination that i dont need, and if i try to lower my values, the scene becomes dark, if you want to see an example, look at my posts here:

post #1

post #2

post #3

 

the 3rd one is the important one where i post 5 renderings (with full furniture & lights).

 

Regards

[Fran]

Thank you Ras. I disagree with Mohamed in that I think your method is a very logical approach and quite useful in the real world. Rather than trying to juggle 3 variables to solve "NP" you have logicaly reduced the controlling variable to 1. And we viz people wonder why we need Math.

[Fran]

the 3rd one is the important one where i post 5 renderings (with full furniture & lights).

Regards

 

If you are using exposure control, try adjusting Contrast to reduce hot spots.

[joske]

you will have to use a different approach interior - exterior scenes

 

exterior you can have 1 skylight (or glowing dome if your using photons) + 1 direct spot for sun (or mr area spot when using photons)

 

do not worry about using spot for sun : place it far enough to reduce the 'spot' effect on your shadows (really u will be the only one who knows, it is impossible to see the diff...)

 

interior is another story :

in real life the sun shadows will be sharp near the windows and wide the further the shadow goes inside, so direct light will be out of the question.

+ you will need photons in interiors (exterior can be done only with final gather if you want), so only option will be the mr area spot light for sun.

 

now skylight will be useless for interior so you will need to produce the skylight effect in another matter.

in real life the skylight is projected inside trought the openings in the wall.

(windows, doors,...) so the best and only light approaching to that, is again Mr area lights. (you need the photons + an area the size of the opening)

so placing a Mray area spot (or omni if you prefer = more time consuming) in front of each opening (and the size of each opening) would be the only way to go.

 

here's an example of that setup :

 

 

and result :

 

 

note that i used omnis in this scene just to brighten up the 2 outside courtyards even if that meant longer rendertimes than when using spots.

if you would like a copy of the scene send me you email and i'll email asap...

 

the idea of 'placing one spot and let the GI solution do the rest' is good in theory, but does not work for GI-interior (at least for mray). if someone does find a workflow like that, please let us know asap... would be VERY usefull...

[Roest]

Thanks guy's!

 

I really learnt something today. i've spent the last month on discovering MR en i'm learning everyday. I had some big probs with lightning my interrieur scene.

 

I'll try these method with putting mrarea lights in front of each window.

[Ras]

Hi Mohammed

 

Well, I really had the same idea about all this when I started teaching and writing up the paper to teach from. To keep it simple my collegue and I decided to go for just one Direct lightsoource and a Skyligt... but it just doesn´t work - I´m sorry but its too timeconsuming and in the end you´ll end up with better results using arealights around the openings in your scene.

 

Often it is actually a very good idea to use two Arealights per opening. One for Direct light with a low coneangle and a hotspot that fits just around the opening. Instance copy this light around the scene to optimize the area covered by the hotspots so that all the photons are put to good use.

Then place a second Arealight that simulates diffuse light from the sky - maximum angle on the hotspot and very close to the opening - fit the area to the opening. Again place one for each opening.

 

This is not faceiosity but just an optimisation that works well with MR. This is in essence a time optimization method - putting the Photons where they should be and taking advantage of the nice arealight effect.

You are of course welcome to pursue the other method but with MR I think you will quickly find out that the quality/time yield is less than optimal.

 

You requested advice for MR -in my experience this is overall the best way to do it - and I owe this knowledge especially to Fran and Joske.

I would characterize myself as a stubborn fellow - and it did take me some time to let go of the idea that a sun and a skylight would be the only way not to "cheat". Fran and Joske helped me a lot in learning MR.

 

In the end you might have to let go of your ideas and analyze the conditions you are working under instead and ajust your methods to it...

 

You don´t get the results you see Joske presenting here - let alone have Autodesk include your artwork in their helpfile like they have with some of Frans work unless you are willing to work rationally.

If you do work using your own methods that produces great images then everything is cool, but you expressed some frustration with MR and I can say for myself that everything became much faster and easier to work with when I adopted this rational approach heavily inspired by Fran, Joske and others.

 

Now for Vray, finalrender or similar renderers the situation is different but they don´t come bundled with Viz or Max. This is definetely a factor when bying 100 or so licenses as we are at the School of Architecture here in Copenhagen. What´s your situation?

[mohamedberry]

Ras...

Thanx for your help here, and many thanx for accepting my opinions open minded well i'll try the way u mintioned here and i'm sure i'll get a good result, the only thing that i was trying to reduce the calculation time & rendering time as much as i can... and using area light on every openning will surely increase it.

 

anyway i'm realy thankful for your advice & will post my tryouts here few days later

 

And many thanx to Joske (yes please mail me the scene m.berry@intermark-corp.com with all the mat & i prefer u archive the file... many thanx again )

 

here is a sample of my theory and settings

[Ras]

Hi Mohammed

 

All in all your render times+preparation will decrease. You should try posting a rendering with the settings you have in the image, then one for the finished tweaked scene and then finally the scene itself.

 

Im essence the "equation" aproach is a consequence of the fact that every scene has completely different Energy and Photon numbers. This is a way I thought of to methodically reduce the time involved in finding the right settings. You might very well be able to come up with another just as efficient aproach but untill then I suggest you give it a try and get to understand what the idea is.

Your parameters for this scene don´t look fully tweaked to me. I especially notice that you have not manually set the radius of the photons and that the energy parameter is only 1. This to me suggests that you have not gone through an evaluation phase - the one where you reduce the size of the photons so that you will be able to make fully educated evaluations of the photon situation in the scene.

 

If you want good results I am quite sure that the aproach I´m talking about (Area Lights over every opening etc) will ultimately decrease render time in your scene. Calculating the AreaLights effect on the scene doesn´t take that long IMO.Tweaking the scene to something decent without it is in my experience a very time consuming activity in itself.

 

Well, post yur results and the scene and we could have a little Mental Ray Challenge with it...

 

How about posting the scene in the Challenge/unchallenge forum and we´ll all have a go at it. Remember posting your render times and preperation/tweaktimes with your renderings.

 

Anyway - I´m working in my own studio the next few days but I´ll edit in som images to back up the text when I get to the Academy.

[joske]

Ras...

the only thing that i was trying to reduce the calculation time & rendering time as much as i can... and using area light on every openning will surely increase it.

 

 

i did try to do something simular a while back, and as a result you need a gazillion more photons and fgather samples to achieve the area effect around your windows (area effect which happens in real live also !) that you end up with unreal rendertimes compared to this solution...

 

if you really have a good "1 spot" GI solution for interior you should be able to do a skylight effect only (no sun) whit only one spot and a flipped sphere to bounce the photons back inside you interior (spot directed to the sky)

if you can achieve a good looking result like that (which i doubt ) and in a rendertime less then a couple of hours... please share with us would be really interesting to know...

 

looking at your setup you will gain a lot more rendertime if you start by optimizing your photon solution, that should look almost as the final result. and will be very fast if fg is turned off (even if u would use area lights for sky)

then add just a tiny bit of fgather (not more then 100-400) to get rid of the last splotches and your scene is finished.

the low use of fgather will determine the speed, not the (lack off) photons or area lights.

so basicly the photon solution is the key for fast and good looking renders in mray... if you can't do that... don't even try to finish your render it won't work... trust me

 

make sure you have units AND system units that are "real". (a chair of 50 units should be 50 centimeters in your scene!!! not 50 kilometers or so...)

if not you won't be able to tell if your photons radius is for instance 75 cm or kilometers. so it would be impossible to have a good photon solution.

 

 

(i'll email you the scene asap)

 

cheers,

phil

[mohamedberry]

Phil...

 

thanx for your tips, but something popedup in my mind today, what if i dont have any opennings !! where should i put my area spots ? use it in its place as the architectural plan ?

anyway, now i am working on a small scene with your theory settings, took time to adjust the values but i am getting something out

 

here is the scene in .max format(after you download this .zip file change its extintion to .rar), i'll be grateful if you try render it and share your settings (that aplies for everyone).

 

almost forgot to thank Ras... many thanx (you are also requested to render the scene )

[joske]

Phil...

what if i dont have any opennings !! where should i put my area spots ? use it in its place as the architectural plan ?

well if you do not have any daylight, you should simulate the light from all artificial sources. then it is probably the area from the lightfixture(s) which you should set.

 

i'll give your scene a go...

[mohamedberry]

i had to change the link... now its working

[joske]

well ... had a look at your scene :

 

units not setup workable

so no photon solution possible

materials are setup very bad

lights are setup bad

models need force 2 sided materials (longer rendertimes)

 

so i guess there is not much good about the whole scene...

 

i'm sorry to be so blunt, but thats how the scene is...

 

if all the above is put in a better way, then you should think about getting a good mray interior light setup... because if you don't, you will never get a light solution that will work in any way...

 

please read my remarks as critisism to learn from, i don't mean no disrespect allright ?

[Ras]

Hi Mohammad

 

Looked at your scene too and the things Philip are remarking on are right. However there is no need to fret. Take one thing at a time. Start with the units setup. To me it looks like the model is approximately 1/1000 of what it would be like in real units?!? Scale it up before anything else. It is very easy to do. Just use Customize/Units Setup/System Units Setup... Set it to meters. Pres Ok and choose a unit setup (as in what units will distances etc be showed in) I always use mm for smaller models like this one.

 

It seems that you are missing some omnis in your light fixtures too. The Areas of the arealights could be tuned a little better to the openings.

 

Render with a standard grey material untill the lighting is about right. This will allow you to spot any errors easily.

 

I still think it would be really interesting to do a challenge on this. Could you do a very basic retexturing with maybe just coloring and repost the scene. Setup a basic direction for a "sun" if youd like some sun to enter the room from the openings. Don´t worry about the arealights leave them as is - we will change them ourselves.

 

The most important thing is to fix the problems with the facenormals, do a fairly neutral texturing, and fix the units setup before we can do a challenge. Remember to include the maps in the Zipfile when you post!!!

 

Will be looking forward to hearing from you again.

[mohamedberry]

Ras, Phil...

 

Thanx for your reply, i noticed the units error and i fixed already but had no internet access to upload the file, i did some rendering though, here is one of them (i'm still learning & trying your theory).

 

the first one with photon raduis of 10.0m & fi sample of 50 (took 15 min.)

the second one with photon reduis of 0.5m & fi sample of 200 (took 32 min.)

 

i will try to fix the model & the material issue (i cant include materials as the files size increases to 10 megas so will use plain colors).

 

PS. i use metric scale (1 unit = 1 meter)

Regards

[Ras]

Hi Mohammad

 

Its looking good!

[joske]

well it's a good start this time ...

you should use photons radius between 50-100 cm. not more

increase the number of photons untill you achieve a good coverage (turn of fg to see)

if the scene is to dark : increase global energy (1-1,5) and / or decrease decay (from 2 - 1,6)

[mohamedberry]

thanx guys, you are realy helping alot

i have a notice here, when i use just photons (no fg) with small radius (0.1m) it looks fine but ofcouese with splotches, so i start using the fg... and then i got a very lightened scen (over exposed) so i had to go back and decrease the energy or increase the photon radius, tell me where i went wrong.

 

unfortunatly i have work now and will postpone these tests till i finish, will be waiting for your rendering (if you fixed the scene your self;))

 

and oh phil, one quistion for you... what is the use of the glowing sphere around your scene, i think there should a light pointed to it so it would reflect it back inside to simulate skylight (if i understand this right) or its glowing will do it all alone ?

 

Regards

[joske]

sphere is mainly for keeping photons from shooting into infinity (shorter rendertimes) and bouncing them back onto your scene

but because it blocks the skylight you give the sphere a glow to achieve the same result (no difference what so ever in result)

 

note that it will not help alot in interior scenes (almost no effect) exept for blocking the photons.

[mohamedberry]

ok guys here is another stage...

 

now i have to finish this scene for my boss, have one or two days maximun to do so, anyway i started using your theory here and i'm going ok, few things need tuning, like the splotches on the window (i dont wanna use a higher fg sample cause it'll increase render time as these 640x480 already tooke 27 minutes each) and i lost the shodows !! i need some shadows under the bed and i cant add any (thats the most important thing, i need shadows)

 

help ASAP

 

Regards

[Ras]

Hi again Mohammad

 

As I have said earlier my own opinion on Final Gather is that it is often not neccesary. In any case - tune the scene without it using only photons and then turn it on if you want. You will not be able to determine where the progress comes from unless you adhere to a method - don´t try to tune GI and FG at the same time.

 

And where is that revised scene of yours? I´m sure it´d be really interesting to see what someone like Phil og Fran could work out with that if they had the time for an unchallenge.