Distributed rendering outputs different colors

[atyss]

Hi!

I started a distributed rendering using the rayhost file. For now only one machine (machine 2)is contributing to the rendering machine (machine 1).

After it rendered 3 frames last night, I checked them and guess what? The parts that machine 2 did are slightly darker than those made by machine 1. The result is an image with darker squares scattered all over. These frames are a complete loss.

Abybody have a suggestion?

Note: The scene is lighted with Final Gathering (skydome technique).

Merci - Thanks
Bernard Lebel

[juan-sanchez]

Hiya Atyss,
I just lost the post (browser crash) I was about to make for you, so I'll keep this short & sweet...
I'm more of a Mac man when it comes to this type of problem, so don't understand the exact ins & outs of this subject area,....
...BUT ....I believe it's to do with your CMS,...try reading the Win help files for details, but it sounds to me as though you're using two slightly different 'colour profiles/calibrations', goto ControlPanels> Display> settings> advanced> colour management for a selection of pre-made selections. (You can form your own on Macs but I'm unsure about Win OSes.)

I believe that the usual 'colour correction' user settings have no effect on the final output as they simply decide how the vid card acts on the colour info passed to it from the OS/apps.

As I said I'm just 'informed guessing' here, so may be off the mark somewhat, so if other peeps reading this have more indepth info I too would be glad to expand my understanding.

Regards : )

[atyss]

Thanks a lot for the suggestion. I'll take a look at it as soon as the opportunity occurs. Right now I'm rendering the last frames on one machine and it's fine. What you say makes sense.

On a side, before going to 3D, I was a graphic designer, and used Macs for years! So I know what you're talking about. God, I missed those days, when everything was so simple.........

Merci encore - Thanks again
Bernard Lebel

[juan-sanchez]

You should take a look at OSX, it's THE way forward.
I've been a Mac man since '89 when I got into graphics etc. just got into 3D with my MSc in the last 18 months...when I built a PeeCee,...but worked on both Win & IRIX at Uni,....obviously loving IRIX as a paid up member of the WinHaters society !!!
...OSX really does give the power of UNIX with a real sweet eye-candy GUI.

I'm going to get into Maya on OSX when I get the time,...then I can ditch this beige-box

-Post back on the CMS thingie as it'll be useful to know for future reference,...if you get stuck I'll help you dig around some more.

[ryan-saper]

It's possible that the problem is the Color setting; but I don't think on PC. Because MentalRay don't use the graphics card for the rendering; only the processor is used... I have the experience of what you talking about, on some Global illumination Scenes, and some Plugins Shader (like Real-Fur). And a Softimage technician tell me it is a typicaly Windows NT (based system, like Win2K) bug. A same file can't be open by multiple applications, or a file can't be access by MentalRay because of a non-absolute Path.
The difficulty is to know which file !!! Because it is a mentalRay Setup file of your scene(and not the the scene itself), something like the lightMap or something...(on your case).
To correct the problem Use Absolute path on a local HD (like c:temp) for all the setup file you can choose a path. And open the scene one time on all the computer you want to use for the distributed Rendering. Maybe you have to start a render on one frame (because it is about rendering setup files, which created only on the start of the rendering). After that, you may start your rendering process on a computer which distribute rendering.
But some bug may still there ! because some setup may re-calculate for every frame... So I advise you to use Biprocessering on WinNT station, the problem is fixed (if you use on computer). Otherwise, you start 2 renders on every computers, and you render a half of the animation on one and the other half on the other computer...

[atyss]

Normally, when I use several computers do render a scene, I dispatch them (using the mental ray standalone on each machine).

In order to allow this to work, I set some environment variables (like the "users" directory and the "home" variable) of each station to a central location, in this case on the main machine (my station). Also, each station has a mapped drive that leads to the said location, and the assigned letter is the same everywhere. When I need to render a brand new scene, I just have to go in the database from one machine, and all the others will use the same DatabaseDir information.

It always worked fine, except for motion blur. The rendered colors are always correct, for each machine.

But in this scene the secondary machines simply can't render a frame by themselves. For example, if I start a frame before leaving for the evening, only my machine will finish a frame (in fact, 2). But the others don't.

So to benefit from the power of all available cpus, I setted up a rayhost file. It rendered faster, of course, but with the problem I described in my first post.

All machines are on W2K sp2.

So do you think there is some more environment variables that I should set to a central location? I don't exactly understand what files you are referring to when you say that several mental ray can't open those files at the same time.

BTW, the scene is lighted with FG.........

Thanks for your help
Salutations - Cheers
Bernard Lebel

[ryan-saper]

As I told you before, it's not about the main database of softimage (which works correctly), it is about the temporary file which MentalRay need to create for the rendering. In your case it may be the 'Photon Map'. Generaly call "(null)", you can set the directory in the PhotonDirector panel, Render Setup>>Global Stting>>Photon Map
You may need to setup a Local directory for each computer, in order to avoid the multiple open file problem, which Windows can't support... You can copy the temporary file in each computer in the correct local path...

[atyss]

Hum maybe I'm wrong but the Final Gathering do not use a photon map. The photon option is for Global Illumination only (I did some tests a while ago and found this).

On the other hand, even if you could save a FG map (like in XSI 2), my scene features a moving character. So a map becomes useless!

Salutations - Cheers
Bernard Lebel

[juan-sanchez]

Asgoarth....I wasn't talking about the graphic card settings, 'colour profiles' although not unheard of on PCs are little used in my experience, Mac's use them to assure of standardised colour appearance from machine to machine.
In a scan>design>print context, and other kinds of 'outputting', they ensure that what appears on one monitor as vivid red, and on another as dull red brown leave the production chain as the same printed colour if they have the same CMYK or Pantone number.

[ryan-saper]

I'm not sure about the Final Gathering, and I expected you use a moving object. So you have to do it on one machine...

About the use of the Graphics card on PCs. I'm sure the most of the PC's renderer doesn't use it. Because each Graphics card use is own Standard, so it's difficult to be sure of compatibility. And I told you about RGB images not CMYK... The Mac are mostly design for Printing (and I don't know how they work...).
I can add that DirectX now include some features for rendering using your graphics card, and XSI is able to use this features...

[juan-sanchez]

Not wanting to get into a squabble or anything, but....

"I'm sure the most of the PC's renderer doesn't use it." -YES, I agree whole-heartedly.
"The Mac are mostly design for Printing" -NO, it's a common misconception held by people who'll admit "I don't know how they work..."

The point I was making is that the colour profile info is not related to the graphic card settings as such, so could have been the source of the trouble.

Cheers