Switching to HDR Lighting in Maya
Up to this point I’ve been using the Physical Sky and Sun for rendering out my scene. But it has it’s limitations. One being I can’t easily tweak the sky itself without affecting the sun, or another way to say I can’t easily adjust the sky fill in the shadows without affecting my key light. By switching to HDR Lighting, this will allow me greater control of my scene’s lighting.
First, we’ll need to get rid of our Physical sun node. Select your camera, then go Window—Hypergraph Connections. Select the Physical Sun and Sky node and delete it.
Now you’ll still have the sunDirection light from the Physical Sun node in Outliner. Since we’ve spent time positioning it, we’ll want to copy it’s position to the new Direction Light we’ll now create. Select the SunDirection Light in the Outliner, set a key on it’s values, and then right click to “copy selected” in the Channel Box those positional values.
Create a new Direction Light, and in the Channel Box, “paste selected” into the channels. The new Directional Light is in the same position as our Physical Sun light. Rename the new light “HDR_Sun”. Turn off visibility on our old Physical sun or delete it.
Under Shadows tab, Raytrace Shadow Attributes; Make sure “Use Ray Trace Shadows” is on for your HDR Sun. Change “Light Angle” to 1, to soften your light’s shadow; Shadow Rays to 3; Ray Depth Limit to 4.
Create your HDR sky. Under the Render Settings, Indirect Lighting, click “Create Image Based Lighting”. In the Outliner a MentalRayIBL (Image Based Lighting) node was created. Now you just need to map your HDR image. You can have your HDR light to emit light from it, but for our scene we’ll keep it off since our directional light is our sun. We’ll rotate our HDR Image to match our sun direction though so that that bounce light looks correct. The HDR image is in a different color space than what our exposure node is doing, so we’ll need to adjust it, otherwise our scene will render too black.
Select your camera, and go to the exposure photographic node; change the CM2 field to 10,000. This will adjust our photographic node to render the HDR image correctly in our scene.
Do test render of your image, you can turn off visibility of our HDR Light to test the HDR sky. This way you can see just what the HDR image is doing alone in your scene. It will look like a slightly overcast day because the the HDR is not emitting Light but creating a natural bounce fill your scene. If you’re not happy with the tone of the HDR under the IBL node, you can change the color gain to a different color to tint your HDR.
Now in our HDR Sun, turn on your sun again.
It’s color is set to white, here too you can tint your sun to be more in line for the time of day your rendering for. For mine I will make it a slightly yellowish sun. You can also increase the sun’s intensity.
For my purposes later, I’m not going to use the HDR sky in my actual renders of the sky. What I’ll do is turn off it’s Primary Rendering, in the IBL’s Render Stats.
So the take away is now I can adjust my key and my fill independently, along with any changes to my Light won’t affect my sky color and vice versa.