Irradiance quality versus resolution

[vermu]

Hi,

Do you usually leave IR quality lower if you are rendering in big resolutions? I mean does bigger resolution compensate lower IR quality in anyway? I am just testing my night scene and with IR values -2/-3 it renders way faster than with -1/-2. With lower resolutions -2/-3 seems abit too low but is it enough with bigger resolutions. I hope you get what I am meaning I am in a thight schedule so otherwise I would do lot's of test renders but now I am trying to save some time asking it here.

[MoonDoggie]

You might want to spread your values out by 1 or so, so instead of -2/-3, use, -2/-4 or -1/-4. This will allow vray to undersample large blank walls and will improve your render quality and time.

Without seeing your render I can't accurately tell you if -2/-3 is much better than -1/-2. I would need to see. Easiest way to do this is to render your image with "Show GI Only". or enable your vray frame buffer and add the render element "VRayGlobalIllumination" and save it out.

As a rule the IR quality is dependent on resolution as you suspect. The default "High" is for small resolutions (640x480, I believe). Everytime you double the resolution you can decrease both min and max values by 1. I usually use -5/-3 for 1920x1080 or so, but it depends.

[vermu]

Thanks for the tip. Seems that -2/-4 is the sweet spot. I have imported vertex model and -3/-5 seems to give alot of light leaks from interior lightning.

[MoonDoggie]

You can possibly solve those light leaks by turning on Light Retracing in your light cache.

Here's the manual:

www.spot3d.com/vray/help/200R1/

Refer to example 4 on this page:

http://www.spot3d.com/vray/help/200R...lightcache.htm

Notice the light leaks around the door trim.

[vermu]

I am just test rendering the image in final resolution. I'll check after the render if the light retracing can solve the problem. Then I could use lower IR value. My problem is just like in that example.

Do you have any advice how to speed up the IR phase when rendering scattered grass. I am using multiscatter. My night time scene is lit with the hdr image in dome light. Lightcache phase goes lightning fast and the actual rendering phase is fast, but the IR is very slow when it's hitting the grassy area. My 3d silhouette trees where slow too with IR, but I disabled all the GI stuff from the trees via vray properties. Now the trees render really fast. I tried the same with grass, but it's slow even then. I can render the whole image without the grass in 3 hours when using final resolution. With the grass it's so tediously slow that I have always canceled the render. I even tried to take shadow casting off from grass but it was still slow. Any advice on that? The same multiscattered grass renders really fast in daylight renders with vray sun+sky.

I can't find that retrace treshold in vray settings. Is it named differently in 1.5 sp6?

[MoonDoggie]

The truth is the bounced light in between grass blades is not incredibly important to the visual and thus the bounced light between the scattered grass blades don't need to be rendered with such precision. To accomplish this you could do the following:

Some options:

1. You can calculate your imap solution and save it with all of the scattered grass off (just have your ground plane instead of the instances). You can then turn on your multiscattered grass patches on and render using the saved solution.
2. You can turn your scattered grass off to GI and render. ("Visible to GI").

Your 3d silhouette rendered too slow with IR? That's very strange...It's just a plane right?

I wouldn't turn off shadow casting from the grass, that will look strange. Honestly, I've never had to do the options I've suggested above. I've never had problems with IMAP generation being incredibly slow. It's quite slow at times, but hasn't been crazy slow like you're describing. It might be some other setting.

I recently had a problem where the option "Use Irradiance Map" was off on one material in my scene (I could tell there was something wrong when looking at the IMAP calculation because that object was a bit dark on the calculation). You might check the grass material for this option being off by accident (this will force that object to be brute forced for the GI calculation).

The retrace option does not exist prior to VRay 2.0.

[vermu]

It seems that my night time settings were not just there cause I am new to vray. I found one site with good general settings. Now the light leaks are gone and my scene got abit better overall lightning. The parts that were really dark before are now better visible. My original settings had one IR pass, now there are 5 or 6 and the result gets finer in every pass. And I just tested there new settings with grass and it renders alot faster. Before I got really fast light cache and slow IR, now I got slower light cache but faster IR but the result is faster overall render.

[MoonDoggie]

Yeah, you want vray to be adaptive and smart about where it samples more and less. Think about it like AA almost.

If you have your irradiance map at 1 pass (-1/-1) or whatever, it's giving the same attention to everything equally. If you were to set your Image Sampler to "Fixed" at subdivs 3 (or whatever) it is doing the same thing, it's anti aliasing everything equally, even if it's just a flat wall with no reflection. This wouldn't be very efficient.

Edit: Also, upping your light cache subdivs can help with light leaks as well.

[vermu]

I managed to get clean nice render after little tweaking. Settings I found caused alot of splotches but the quality and speed were good. After quite a tweaking and testing I found out that IR treshold values were the key. I had to lower the values to 0,2/0.05/0,05 and use world space in lightcache. After that all the splotches were gone. Now I am happy with the exterior lightning and the mood. What kind of lightning do you suggest for the inside? I have now vray plane lights but the mood and the feeling of the light is not balanced. It's looking really nice outside but artificial light inside is not on par. I am testing now photometric lights.

[MoonDoggie]

Balanced? What do you mean? You mean having the same visual exposure for outside and inside? It's really not possible in reality.

Here's an example if it's indeed what you're talking about:

http://www.westelm.com/products/leat...y=call-bedroom

Photometric lights won't help your interior lighting necessarily. It's just give you interesting cones on your walls. Let's see a render?

[vermu]

Here is what I got. I am happy for the result as it's one of my first vray renders. Do you want to give some feedback? Saying it was not balanced I meant the interior light was too washout and didn't have the needed intensity. Attached image is better. I saw some night shots on peter guthries blog but couldn't get the same interior result. The blog pic was really nice.