Wrong Shadows

[liv-k]

Hello everyone

I have a problem with my shadows behind a painting. As you can hopefully see at the picture attached, there's no dark area behind the painting it's just a line that looks like a shadow although it feels so wrong! Can anyone tell me what am I doing wrong?

Thanks in advance!

liv-k

 

[SLW210]

It does not appear to me that you have a light shining on the picture. Did you use 3dsMax for the entire picture?

[liv-k]

It does not appear to me that you have a light shining on the picture. Did you use 3dsMax for the entire picture?

No it doesn't have a direct light on the painting if that's what you mean. I thought indirect illumination has the same results; no? I have a daylight system that illuminates the room and final gather. Do I have to put a direct light to have a proper shadow?

[SLW210]

As you noted, you do have a slight shadow, I would only think that getting more light on the subject would produce more of a shadow and I do not think you need a direct light just more light.

[Cad64]

Can you provide some unrendered screenshots of your scene? I would like to see how you have it set up. Or better yet, post your file.

 

If you're using a daylight system, and you have 4 walls, a floor and a ceiling, how are you getting light into the room? Are you using sky portals at the windows?

[liv-k]

I don't use sky portals I use final gather with 3 bounces for indirect illumination. At the first screenshot I have the picture right after the light calculation and just before the rendering. You can see that there is a quite realistic shadow around the painting. At the second screenshot after the render this shadow is weaker and thinner.

 

 

[liv-k]

I tried to use sky portals and now I can't see the background. I usually work with final gather so this was an unexpected problem for me and no matter how I searched I haven't solved it yet. If anyone could help with that too I'd appreciate it! thanks!

 

[Cad64]

I'm guessing that you've probably got too many bounces going on. If you're using 3 bounces, then the light comes in and hits the floor and bounces to the wall, (1st bounce), comes off the wall and onto the back of the painting, (2nd bounce), comes off the back of the painting and back onto the wall again, (3rd bounce). That's probably what's washing out the shadow. Try 2 bounces and see if you get a better result.

 

Have a look at this tutorial. Might be helpful: http://www.cgarena.com/freestuff/tutorials/max/livingroomlighting/lighting.html

[liv-k]

I'm guessing that you've probably got too many bounces going on. If you're using 3 bounces, then the light comes in and hits the floor and bounces to the wall, (1st bounce), comes off the wall and onto the back of the painting, (2nd bounce), comes off the back of the painting and back onto the wall again, (3rd bounce). That's probably what's washing out the shadow. Try 2 bounces and see if you get a better result.

 

Have a look at this tutorial. Might be helpful: http://www.cgarena.com/freestuff/tutorials/max/livingroomlighting/lighting.html

 

Ok thanks I'm gonna try it as soon as I get home. Amazing tutorial! As for the sky portal problem is there an explanation?

[Cad64]

Did you follow the sky portal instructions in the Max Help files?

 

I normally add my backgrounds in Photoshop, post render, but here's a tutorial that may help explain how to use sky portals: http://www.tylertreat.net/blog/?p=482

[spittle]

I think you should try creating an ambient occlussion pass - google it. And overlay this on top of your render in your photo editing application. This is faster than upping your render settings.

 

If you're using mr Arch Design materials then you can try enabling this here (under special effects), and again remember to set the distance. The first way is probably the best however it requires some post but but this is pretty straight forward.

[liv-k]

Did you follow the sky portal instructions in the Max Help files?

 

I normally add my backgrounds in Photoshop, post render, but here's a tutorial that may help explain how to use sky portals: http://www.tylertreat.net/blog/?p=482

 

I think you should try creating an ambient occlussion pass - google it. And overlay this on top of your render in your photo editing application. This is faster than upping your render settings.

 

If you're using mr Arch Design materials then you can try enabling this here (under special effects), and again remember to set the distance. The first way is probably the best however it requires some post but but this is pretty straight forward.

 

Thanks for all your answers.

 

1. Cad64 I reduced my bounces to 1 and I still have the same results. I attach 2 test renders where you can see the process of the image right after the final gather and just before the render. It seems that it calculates the shadows correctly, but for some reason when it tries to render it it smooths it too much. I moved the painting away from the wall in order to create more space between the painting and the wall and as you can clearly see there's no shadow only at this particular spot behind the painting. I've searched everywhere and I just can't explain it.

2. Spittle I've been using ambient occlusion from the beginning through mr Arch Desing mat. The painting's width is 5cm and the ambient occlusion distance is 2cm so I don't think that helps it.

3. The only way I can get my shadows correctly is by using sky portals, but in this case I can't see my background. Cad64 I've checked the link you sent me about sky portals tutorial and I don't think that I miss something there. I brightened my picture, in case it was an exposure problem but with no success. The results are the same.

 

Is there a possibility that my file is corrupted in any way? Again thank you all for your time and help!

 

1st photo image after FG calculation where you can see the shadow calculation

 

2nd photo image after the end of the previous FG render with 1 bounce and no sky portals or GI where you can see how smooth the shadows become

 

3rd photo image with sky portals and FG enabled where the shadows are correct but the background disappears!

[spittle]

Well it looks like the picture is further than 2cm away from the wall so AO won't work at this setting. So I don't think AO is the right solution.

 

Do you have the same problem if you hide the glass for your render?

 

Can you post some of your settings for Exposure Control, FG settings & your background setup?

 

And have you looked at the various mental ray documents on the mental images website? They do a step by step for a scene setup similar to yours.

[liv-k]

Well it looks like the picture is further than 2cm away from the wall so AO won't work at this setting. So I don't think AO is the right solution.

 

Do you have the same problem if you hide the glass for your render?

 

Can you post some of your settings for Exposure Control, FG settings & your background setup?

 

And have you looked at the various mental ray documents on the mental images website? They do a step by step for a scene setup similar to yours.

 

Well I think I found what's wrong with the sky portals. I found this tutorial here http://bimuzer.com/ where it says:

"There’s light coming in from the exterior, but the Environment Map that we’ve created (ie. the background image), appears to be totally black. The reason for this is that the Exposure Control settings is reducing the light that the image is supposed to be giving off. Therefore, within the Exposure Control dialog box, with mr Photographic Exposure Control set, within the Physical Scale group, select Unitless and set the value to 100000..

So with a value of 15000 at the physical scale settings the background seems to be just fine!

As for the shadow problem I can't solve it. I've checked numerous tutorials and I don't understand what I'm doing wrong. I'm posting FG and exposure control settings. I've also rendered without the balcony doors and the result is the same.

Thank you!

[liv-k]

Could it be because of the position of the sun? I moved it and shadows seem to become much stronger now.

 

 

[spittle]

Have you tried overriding your materials to a matte white in render settings while you adjust your lighting? It'll save you render time and will be easier to identify problems - you'll have to hide your windows.

 

Looking at your last render I think a separate AO pass is what you needed, saying that, if moving the sun has fixed the problem then I guess that will do but you obviously won't get to the bottom of the original problem. Obviously having direct lighting on the wall will give you a crisp shadow.

 

Below is a quick demo, notice the first image suffers from floating objects, and compare to the last image with the AO multiplied over the top set to 30% opacity. You can see the subtle contact shadows which I think is all you need.

 

 

Nice looking scene though, would be cool to see the final render - how have you done your tree?

[liv-k]

Have you tried overriding your materials to a matte white in render settings while you adjust your lighting? It'll save you render time and will be easier to identify problems - you'll have to hide your windows.

 

I've tried it now that you mentioned it.. The same thing happens here too.

Looking at your last render I think a separate AO pass is what you needed, saying that, if moving the sun has fixed the problem then I guess that will do but you obviously won't get to the bottom of the original problem. Obviously having direct lighting on the wall will give you a crisp shadow. Below is a quick demo, notice the first image suffers from floating objects, and compare to the last image with the AO multiplied over the top set to 30% opacity. You can see the subtle contact shadows which I think is all you need.

 

I'm experimenting with the render options and what I realized so far is that sky portals along with FG give a more interesting shadowing of the room. The thing is that if it was some material or object problem the shadow would be smooth in both occasions. You're probably right about the AO pass. Maybe this is what it needs. I'm guessing that you mean to apply it on photoshop. Thanks about the demo by the way. I'm not so familiar with all photoshop's tools so I'll try to correct it as much as I can in max and if I can't I'll google it... Below I attach the 2 renders (FG - FG+sky portals) where you can see the difference.

 

Nice looking scene though, would be cool to see the final render - how have you done your tree?

 

Thank you very much it's my first serious attempt! The tree is from Max geometry-AEC Extended-object_89 foliage objects with some random settings about the height and the density of the foliage. I played with the materials with high reflectivity (0,7-0, and reduced glossiness (0,3-0,5) and for the trunk I used a wood map. Nothing special it's the distance that makes it look realistic concerning the materials, but if you want something more specific just let me know. I'd be glad to post the final render if I ever find what's wrong with the shadow thing...

 

Thanks again for your help!

[spittle]

The floating objects are due to low quality render settings, or should I say a scene that requires higher FG settings and the sky portals focus the FG on the interior of the scene hence the improved quality and increased render time (my scene would have benefitted from sky portals).

 

Maybe have a look here; this guy knows his stuff: http://3dsmaxrendering.blogspot.com/2010/07/efficient-interior-lighting-with-mental.html

 

RE AO in post - it really is pretty straight forward. You can download a free paint package called Gimp. You need to work out how to place your AO render above your main render (copy/paste), then just change the blending mode on the AO pass to multiply and adjust the opacity to suit.

[liv-k]

The floating objects are due to low quality render settings, or should I say a scene that requires higher FG settings and the sky portals focus the FG on the interior of the scene hence the improved quality and increased render time (my scene would have benefitted from sky portals).

 

Maybe have a look here; this guy knows his stuff: http://3dsmaxrendering.blogspot.com/2010/07/efficient-interior-lighting-with-mental.html

 

RE AO in post - it really is pretty straight forward. You can download a free paint package called Gimp. You need to work out how to place your AO render above your main render (copy/paste), then just change the blending mode on the AO pass to multiply and adjust the opacity to suit.

 

Ok you were absolutely right. It was all due to low FG precision settings. And sky portals just transfer light a little deeper in the scene. That's why it was easier to calculate the shadows more precisely. So simple I can't believe I've been searching for that setting for 3 days now.

 

I checked the tutorial... The guy certainly does know what he's doing. Amazing stuff thanks a lot.

 

I guess now I can have a satisfactory render so I'll post the final one as soon as it's ready.

Once again thank you so much for your help!

 

[spittle]

Using the high FG setting is really unefficient though and takes ages. I would persevere with the separate AO pass.

 

This book will help you a lot:

 

http://www.amazon.co.uk/Mastering-Mental-Ray-Techniques-Professionals/dp/0470563850/ref=sr_1_1?ie=UTF8&s=books&qid=1297407344&sr=8-1