Advanced Lighting Help (Been Looking For Hours!)

lemoncoconutcake

Hiya,

Looking for any help to shape and block out light in areas of scenes, to control it more. Products, methods, tips, anything really. I've spent hours searching products and forums without luck. Basically the holy grail would be something like the light block filter in Arnold. But I'll take GOBO tricks, lighting methods, clever workarounds, anything!

First thought was to use flags, like in photography. So I tried using geometry like planes in front of lights, but they forever to position and have a very sharp edge on the shadows (Would curved geometry soften these edges?). Then looked at some GOBO products on the store, but they only seem to add some cool patterns. Finally I wondered if the emissive lighting packs could be used for making lights that create an even beam of light, that doesn't leak too much over distance (Like a God-Ray but with a customizable shape). But I don't know enough about Daz yet to figure out exactly what each of the lighting products can do.

Add to that hours of searching the forums, and I give up. Can anyone help out?

Richard Haseltine

Sharp sahdows are a prodct of the light source (point, or very small shape) rather than the object casting the shadow.

If you are wanting to exclude certain items, rather thana reas of a larger item, one option might be to use Canvasses with Light Path Expressions - that's in the Advanced tab of Render Settings, nVidia has docs on Light Path Expressions (LPEs).

JonnyRay

My rule of thumb as I setup lighting for Iray rendering is to follow this process:

1. Start with environmental lighting. Whether that's an HDRI or the Sun-Sky dome or some distant lights. My overall intention is to define how much light I want in the darkest part of my image.
2. Add scene-based lights. Candles, lamps, fires, etc. These could be a matter of making sure emissive surfaces are enabled or it may be adding some point or spot lights as necessary. Sometimes I will swap existing light fixtures with KindredArt's Iray Ghost Light Kit 2 props which tend to render a little faster than emissive surfaces.
3. Add additional light where needed. This is where I add in my Ghost Lights. While I typically use Kindred Art's Iray Ghost Light Kit (or Light Probe Kit if I want to light a larger area), both of these products are really mostly time savers. It is possible to create your own by just using some primatives, google searches will find guides for this.

Basically, I find it easier to build up lighting where I want it rather than trying to take it away from where I don't want it. Iray approximates the way that light works in the real world. To block light from parts of your scene, you'd have to figure out how to add some geometry to keep the light from going there. It's much easier to ADD non-scene motivated lighting with ghost lights and light probes than to try to take light away.

All that said, if you absolutely MUST control which objects are lit by which light sources, you're certainly going to be looking to do that in post processing with Iray Canvases (and probably LPEs) like Richard suggested.

lemoncoconutcake

While a little advanced for a noob, you could really have some fun with those LPEs.  Unfortunately I'm not sure it's exactly what im after (my fault really for badly describing it).

Basically I'm coming from watching a tutorial where a pro went to town on a project, very meticulously raising and lowering the light in areas of the scene. Shaping the shadows and lights for leading lines, contrast, values, all that good stuff. He used those light blockers to carefully control light in areas he needed to be darker. Now I understand how to do some of that from photography, with things like flags and reflectors. But 3D and Daz is a whole new world to explore and have fun with, so that's why I'm here (and trying not to cheat by doing it in Photoshop!).

Thanks for the tips so far, think I'll definitely try out the ghost lights and soften up my lights a bit.

Is it possible to create a primitive that is invisible to the renderer, but blocks light? I have a feeling LPE *might* be able to do it, but couldn't see from the expression examples (that and it all looks like Spanish to me right now)

Sevrin

Well, if you want advanced lighting, your best choice is to go with canvasses.  I give a basic example of what you can do by varying the levels of light sources in this thread.   You don't need to write out your own light path expressions to start, since the DS implementation of Iray includes a lot of basic options, so don't let talk of LPEs put you off using canvasses.  I think bringing up LPEs first thing when discussing canvasses in Daz Studio with beginners is unhelpful.  They're very powerful, but often unnecessary, because Daz has done a lot of the work for us.  The only problem is that Daz has been terrible about documenting this stuff.

For example, the basic canvas is a Beauty (LPE equivalent "L . * E" with or without spaces, i.e., whatever light bounced all the times that hits the camera) canvas.  That's just the scene however you have it tone mapped, or not tone mapped.  You can also go to the node control, and create a node from whatever you currently have selected.  That canvas will only include the selected object, which can be handy for isolating figures for stuff like creating masks.  Then you can go to Light Group, and select each of your different light sources to create separate lighting nodes.  You will get a canvas with only the illumination provided by that source.  You can have an  Environment canvas including only the light provided by your environment settings.  You can use specular canvasses with or without node selection to get the twinkly and reflective stuff just so, depth canvasses for masking FX, etc.

With DS Iray, you would only use LPE if you need to isolate how the light from source X falls on target Y, and frankly, that's super easy to achieve by masking.   I'd only bother with writing your own LPEs once you've exhausted the possibilities of the presets.  For example the LPE "E.*Le" gives the same result as just selecting Environment Lighting from the dropdown, which also conveniently gives you a canvas with the words "Environment Lighting" automatically, which LPEs do not.

Oh yeah, and using canvasses is an additive process.  It's light path expressions, not dark path expressions.  You're not blocking light, rather you're choosing what light and how much of it to include.  To block light, you'll need dark in the form of masks unless you can make offscreen flags work.

shaneseymourstudio

I have had difficulty using flags as well to block off light. I can eventually get something I am happy with but it takes awhile to do. One thing I picked up on from a product I purchased awhile back, forget the name and not where I can check it, was they basically built geometry around the light similar to a softbox using planes on the sides and one on front of light that was setup in materials so that it acted like a diffusion for the light to soften and scatter while the sides and back were black. I am not sure the settings for the diffuse on front.

 

I have mainly used IES profiles on spotlights that I place on existing geometry for the soft shaped look I want or if I need only specular in some instances such as eyes I will setup a spotlight and set it to only apply to Specular and place them in the scene so that I don't have to have harsh light on the whole character. Once you add the spotlight it will be an option from the top drop-down of the "Light" under Parameters tab.