Rim lights! - Solved

Dax Avalange

Hi all! After solved the issue of red eyes with the help from Daz users a new question here on Daz forum. Easy, fast, and I hope, easy to solve question.

I need to place around my characters a rim light. Like the halo when you get the sun behind you at sunset, or penumbra under a street lamp.

I don't like to use the ready scripts, II prefer free hands when to place lights, cams, and characters in my scene.

I'm using iRay.

 

Thank you!

DrunkMonkeyProductions

the simplest and fastest method is to use a really high intensity, 1000000+ lumen spot light less than 1m from the character.

depending on the subject using the rectangle option set to a size that is hidden behind the character, for front shots, can help.

Another option is to use lower intensity spots but using more of them to outline the character.

the worst i've had with that approach is about 25 spots set to around 100000 lumens per. Lower spread angle, about 30, and just enough distance to allow the light to actually illuminate the character.

In this case i don't have the center point on the character but just glancing. View through the light and have the dot just slightly off from the character.

Just make sure it's always higher than your key and fill lights.

the drawback to this method, or just about any, you'll probably have to adjust the translucency of the character

 

the penumbra effect you'll get naturally, but can enhance it by using lower intensity lights set at different angles, with the center most light at the highest intensity and dwindling from there.

10-15 degree offset should be ok.

Of course all of this depends on what the scene composition is and what you're trying to achieve.

 

 

Dax Avalange

Thank you DrunkMonkeyProductions. I will try the options you xplain. The thing I'd want avoid is the full front light. I mean, when I point the spotlight on the back of character instead lighting the profile of her, I see the front light even. Like if I point a spotlight toward her. I use milion of Lux to get a bright outline.

DrNewcenstein

If you have knowledge of real-world lights, you might want to consider setting the Luminance Units to Watts instead of Candle based factors. It's just easier for me to call a ceiling light 100w multiplied by the number of lights actually in the ceiling.

Redz

If you are getting an unwanted front light, it’s  worth checking in the camera parameters that the camera headlamp is turned off, and also that headlamp is set to ‘never’ in your render settings. Other than that it could be that you have an HDRI providing lighting to the scene. Choosing ‘scene only’ as opposed to ‘dome and scene’ in the Render settings, environment, may help with this. 

Dax Avalange

Merry Christmas and Happy NewYear everybody.

Forgot to say my scene is completely outdoor.

DrNewcestein, I'm electronic technician and I know about watts and lux, but probably I missing something about this. This is a software and any device need to adjust parameters to make everything work. Where t switch watts? Thanks for the tip.

Redz, first thing I do before build the scene is to be sure to turn off the headlamp of the camera. So,  the strange fact, when I place the spot behind the gal, incredibly she got a front light (body and face) , the same light of the spot. I'm sure about this because color is little bit yellow, xactly my the same of the spot. Anyway your second tip is intersting, cause I just using 'dome an scene'. So I try to switch on 'scene only'. Let you know.

DrNewcenstein

Luminance Units is set on the Emission property, right below where you set the Luminance. Drop down to the "W", and that's yer Watts.

 

Dax Avalange

Really thanks DrNewcenstein!

Tobor

Rim lighting in Iray isn't as direct as it ought to be. There are some known issues and artifacts to contend with:

1. If the light is positioned toward the camera such that it goes through a transparency (hair is common), the geometry of the object will become a full blown-out white. You need to move the light slightly off-axis as needed.

2. A very strong rim light may cause problems with skin textures; specifically, you may get a change in glossy characteristic between the torso and leg textures. 

3. The skin shader you use will affect the subsurface scattering that creates a "halo" around the figure. Some shaders handle this better than others. You may find a light striking from the side (the 2 or 10 o'clock position, for instance), rather than from the rear, provides the look you're after.

4. In certain circumstance, a low mesh resolution the most common, side or back lighting can create what's known as shadow terminator artifacts, endemic to Iray and renderers like it. These are jagged interruptions over the surface of the object. Upping resolution can help, as can reposiitioning the light.

A note on using Luminance Units: this applies to mesh emissives only. The "built in" light sources (spot, point, distant) don't have this setting. For spot and point light, the units is fixed as lumens per centimeter square; for the distant light, it's lumens incident per square meter (applies to 4.9/later; it was per square centimeter in 4.8).

Dax Avalange

Thank you for your tips Tobor. I'll try to move the axis on the side instead back also, usually I think to place the light from back like the real to get rim, but in that way character is too bright. About point 4 the shadows artifact I avoid the fragmented shadows usually using hi res at 2 or 3 point mesh resolution (I use low res just to try the lights when the scene is full of meshes). Going back the rimlight, when I'musing the default iRay render settings only, (Ruins HDR) seems like the rendering is more clear and sharp. I can see any bump and normals details. I wonder if the settings or HDR map do that.