Help with Iray Interior Scenes using Mesh Lights
tring01
Posts: 305
I've been doing renders for a web comic recently using IRay. The results for exterior scenes using Sun Sky lighting only are very nice and render in a reasonable amount of time. My problems come with interior renders.
I tried using three point photometric light setups and just could not find a way to handle the harsh, obvious shadows without way too much time consuming fiddling. I switched to mesh lights. I generally use just a single 1 meter emissive sphere. Produces a really nice render and lets me get setups done in minutes. I still have one problem.
I can't seem to get a handle on how good is good enough when using mesh lights. I find the convergence percentage a good indicator of quality for sun sky lit renders, but interior mesh light renders never get above 1% to 5% convergence. The renders LOOK fine to me but I keep waiting for that convergence percentage to come up to something reasonable. It just never budges, no matter how good the render looks to my eye.
Can anyone suggest a render setting tweak that will give me a more useful measure of render quality for these interior mesh lit scenes?
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Comments
Really, it doesn't matter...if it looks good to you or for your purposes, then call it 'done' and move on. No sense spending more time than you need to.
True, true. But I like to rely on something more objective that how the render looks to my eye. Perhaps it's the perfectionist in me, but I would trust a good mathematical measure better than my eye any time. Especially since the render window is pretty small scale. I can't really see good detail until after I save it off and view it at full resolution. It just bugs the heck out of me that that progress meter never moves.
...I've found that interior scenes take longer in general than exterior scenes using an HDRI sphere or the Iray Sun/Sky. I did one scene using Magus Manor, 6 characters, 8 mesh lights and 5 photometric spotlights which took over 6 hours to render. at 1,200 x 960. For a good portion of time the progress meter looked like it was stuck at 26% convergence for hours even though it was still rendering. Most likely, all that light I had bouncing around was the culprit, but most of the mesh lights were visible and had to illuminate various areas in the scene so I couldn't just get away with one.
Try adding geometry to your photometric lights. You can easily make them emulate softboxes of any size, for example your 1 meter emissive. Just change the geometry from point to disc or rectangular, then modify the dimensions to be the desired size. Just remember that Studio's default dimension is cm.
These lights work like real lights. Bigger and closer equal softer shadows.
One other point, more lights, in Iray, equals faster renders.
You can cheat with interior scenes where there is little or no reflections by using an iray section plane node to slice through the interior walls out of view, and then let the light from a HDR come through the now "open" walls.
Whilst this is not simulating real interior lights (but then a 1m mesh light is also not real), it can still look realistic if the HDR is giving more evenly spread light, and is thus simulating the light bouncing off the missing walls. This method will normally render much quicker than using simple mesh/photo lights.
I experimented with this approach with little luck, but I always thought moving the lights further away was better. Got to try your approach. Thanks.
Will the section plane keep reflections intact, or will what's invisible be invisible in reflections, too?
Not sure, but now I think about it, I think it does keep the reflections, which is why using an iray section plane node is often better than just hiding the walls.
Whoa...this sounds like an amazing idea. Problem is I have no idea what an IRay Section Plane Node is. Can you please give some more information about that?
Wow! I found the IRay Section Plane Node. I created one and placed it in the center of my camera. Then I parented the camera to it. Now I move my camera anywhere in the scene I like and all I have to do to get good overall lighting is fiddle with the tone mapping a bit. Maybe add a spot light as an accent light. The renders run much faster and look a lot better. This is just amazing. It's going to save me hours and hours. Thanks so much!
I am glad it works so well for you. As I said, it is sort of cheating, but if you like the final affect (and the lower render times!), that is what matters most.
There's no reason for it not to work. Iray is following physics -- the larger the light source, the less sharp the shadows. "Focused," convergent (or parallel) rays are what cause shadows, so a wider emitter will get rid of them. For general illumination, it's better to use a flat geometry for Spotlights; you can use flat or spherical with Point lights (3D geometry with spotlights do weird things, and while useful, can be frustrating if you aren't expecting it).
Another way to control shadows is to use IES profiles with Point lights. You can get free profiles on the Web. See mjc1016's sig line for resources.
Not really cheating, as this was the mainstay in movies for years before the indoor stage, and all its very hot lights. The old flicks were shot out in sunlight. One of the reasons the movie industry moved to LA from NY and FL was the more predictable weather. They'd put netting overhead to soften the shadows, or shoot by rotating the set on the non-sunlit side. Today, most artists will prefer natural light from a large window or skylight over any artificial lights from lamps. It's just a more natural light.
A (properly made) indoor HDRi should replicate the light quality of an indoor scene. So leave off the ceiling (or cut it with the plane), and let the light in that way. You can always fill with light fixtures as needed.
If Clip Lights is off for the plane in the Parameters pane then light will be let in but the clipped areas will not show in reflections; if Clip Lights is on the reflectiosn will show but light will be blocked (so useful for awkward camea angles but not for lighting). Off is the default.
Photography lighting books / tutorials are your friend.
As Spooky and others have said, more lights will be better. Note that tone mapping can make the scene brighter but is not more light (from the Iray perspective).
A note on removing a ceiling to allow an outside HRDI to illuminate an interior - the light will travel down the walls in an unrealistic way, so you need to block that light by placing a plane (or several) around the tops of the wall/s so the light is restricted more to the centre to the ceiling area to simulate an internal ceiling light. The same goes for removing a wall, as windows rarely extend all the way to the wall edges.
As for more lights the better, I think that should read, the more light the better with redard to render times, not the actual number of lights.
...not if they are emissive lights.
...is this a 4.9 addition? I'm still using 4.8 because I don't wish to recalibrate all the skin shaders for my characters.
...from a conceptual standpont I find that emissive mesh lights are more "elegant" since a light prop can be turned into a soruce of illumination without having to position an array of point/spot lights to "fake" it as had to be done in 3DL.
I have to agree with that statement. Unless you need an outdoor scene that requires a sun. But for indoor renders I pretty much exclusively use emissive lighting.... and wait... and wait.... for it to render. Sigh.
Conceptually, yes, but still more practical to be more fakey. ;)
No, Create>Iray Section Plane.
Would the IRay Light Portal feature in 4.9.2 be a comparable solution? I haven't tested it out, but in reading about it in the 4.9.2 release thread, it seems as though you can define a "window" by using a point or spot light (whose geometry is set to rectangle) and that this then tells the IRay renderer to allow sun/sky/HDRI light sources to affect a scene's interior (provided the Caustic Sampler property is enabled in the Optimization group under Render Settings).
Unless it's an unusual shape, you can make a point light act as the center of a light bulb by changing its emitter from point to sphere, and size adjusted accordingly. Non-planar emissives tend to be very "pricey" rendering-wise, though you can help there by reducing the number of polygons in the shape. But then, that doesn't make for a very realistic looking light bulb. (Unless your light bulbs are supposed to look like dodecahedrons.)
An advantage of an emissive source is that it's easier to see its size when you're preparing the scene. But that's just an advantage only in scene setup. I would rather take an extra five minutes futzing with the scene, then to take more time in the render. You reap what you sow, especially with a labored machine like the one I have (<500 cores).
Both point lights and emissives can take an IES profile, which produces the most realistic look. Since the built-in light types are generally the most efficient, as they are part of Iray and are optimized for what they do, a good approach is to use a point light for the actual scene lighting, cranking up the value as needed. Use the emissive with IES profile for the on-screen appearance, and the "drape" that the light cone from the source provides.
Always bear in mind that emissives do not provide scene lighting in Interactive mode (they glow only, but do not produce illumination into the scene). If you ever wish to use that mode, for shadow control, for example, and your scenes are built using emissives, you'll be out of luck. You'll have to replace all those light sources.
Finally, what Daz really should do is not rely so much on Iray Uber, and create a set of simplified shaders for applying to emissives. What people tend to do is take some arbitrarily shaded surface, and then simply turn on the emission color. Depending on the other settings in the shader, this can lead to horribly slow render times, because the other settings "compete" with the emissive function. Barring a single-purpse shader, it's important to always first apply the Emissive shader, which resets everything. You can then adjust the color, light output, etc. Unless you need a very unique look -- a reflective surface on a clear light bulb, or example, leave the other stuff alone.
It can speed up render time, but it won't produce better results (given enough rendering samples). The portal function is a biased "hint" for telling the renderer to give a higher weight to the light that is on the other side. It doesn't itself produce light. The hinting overcomes a limitation in Iray related to indirect lighting -- it's a similar function the architectural sampler, which also helps in similar situations.
I don't yet have 4.9 installed, so I can't directly test, but I find it curious that the caustic sampler (another hint) has to be turned on. I know this is what the Iray programmer's docs say, and I wonder if it's a typo -- they instead mean the architectural sampler, which would make more sense, as these functions perform similar duties. For someone with 4.9, it would be a worthwhile investigation to verify this.
...I have a couple emissive shader sets that work pretty good. as they produce the correct the colour for various standard types of lights. Never messed around with IES profiles. Have a couple freebie sets I downloaded but don't know how they need to be installed. I rarely if ever use Interactive mode, I'd rather just go to 3DL in that case.
Using emissives in a set like Jack's Library would be far simpler to set up than having to place a point light in each one of the lamps and it would give a more "believable" look as the bulbs wouldn't cast shadows. Guess there's always has to be some kind of trade off to deal with though. Simpler setup - longer render time, more complex setup - shorter render time.
Yeah, really need a GPU with more horsepower to get away from CPU rendering which would speed things up a bit. Sadly, one that would work well for most of my scenes costs about 1,000$ (the 12 GB Titan-X).
Finally got around to experimenting with photometric lights as suggested. I was surprised to find that the point light, which I never had much use for in 3Delight, is a great choice for providing area light to an interior. I changed it's profile to sphere, it's size to 100 (1 meter diameter), and set the lumens at around 5,000,000. It does an excellent job lighting up the room and doesn't take anywhere near the time to render as a similar mesh light would. All I needed was my point light and one spot light for fill and I was able to render all my scenes in that room with very little fussing.
Thanks for the advice! This has been the most valuable thread I've ever started. You guys are all so great at sharing your knowledge. Thanks again!
Point lights also take IES profiles, which can produce wonderful results. Worth some experimentation.
Was dreaming about a Quadro VCA until I had a glimpse on the pricing, around €45,000,-. After recovering from the followed hemoptysis and 99 nervous breakdowns I got that 8 Titan-X's would be a lot cheaper, providing the same renderpower, 12 GB VRAM and 24,576 CUDA cores, but a mainboard which you could put them onto would still be have to invented.
This comment inspired me to test something, and it has helped a LOT!
One fo my problems with using the sun-sky lighting is it too can cast harsh shadows that I don't want. I got to thinking about your comment. I made some primitive planes and applied the iRay uber base to them. A plain white plane acts just like a photographic reflector panel! Want a fill light for an exterior shot? Just whip up one of these cheap reflector panels and put it down sun of your subject. Voila! beautiful soft fill light and with no messing about with spot lights and such. You can even change the base color of the plane to add color temperature to your reflected light.
Sun casting harsh shadows? Whip up another primitive plane as above and put it up-sun. Set the cutout opacity to something less than 1 (say. 0.8 or so) and voila! Shadows are gone! If your scene is a bit dark just go to tone mapping and decrease your F-stop as necessary.
This just tickles me! Using virtual screens and reflectors just as one would in reality. This is like playing a photography video game or something! Ha!