30 June 2020

UE4 Lighting Breakdown: Tips and Tricks – Rob Simpson

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Introduction 

 

Hello, My name is  Rob Simpson. I’m a Junior Lighting Artist at Sucker Punch Productions. 

 

I recently re-lit Aiko Shinohara’s Library UE4 scene, My goal for this exercise was to continue to improve my lighting skills and practice a new workflow that used physical lighting units and exposure value in Unreal. I will be breaking down my process from reference to color grade. 

 

Why physical units?

 

Physical units are non-arbitrary values that have a lot of resources available online. These values can be useful for getting you 80 to 90 percent of the way there when shooting for a realistic result. Physical units also provide consistency with light fixtures, as well as some game studios have begun to adopt this approach to lighting levels in their games.

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Reference & research

When I start a project I set out to gather references on mood, color, and composition that will help inform my decision making while lighting. I knew I wanted to create a rainy interior scene with soft natural light and, a complementary color scheme between warm and cool light.

Colorandmood-Ref.

Another aspect of my research was gathering information on what sort of target exposure value would best suit my scene and the Lux values typically used in this sort of real-world lighting scenario. My scene came in about 2000 Lux and Used an EV of 6.

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Scene Prep

 

Typically when I start work on a scene I will place a post-process volume set to unbound and remove adjust rendering features like bloom and vignette to zero so I have a clearer idea of how my lighting is affecting the scene.

 

If the scene does not have a Lightmass Importance volume I will add it to the scene along with Lightmass Portals in windows or similar openings where the light will pour through. Be careful though because more Lightmass Portals will increase your bake time. I will also inspect the lightmap resolution of the scene and adjust if needed.  

 

I also use this time to establish some camera angles and set my exposure in the viewport to an EV100 of 6. Interiors are typically somewhere between 5-7

Primary light sources

 

When lighting a scene I purposely start out with as few lights as possible and only add more if I really think I need them. It can be easy as a beginner to have the urge to just place a ton of lights in a scene. I want to be methodical and try to make the light feel motivated and grounded. That’s not to say there isn’t room for faking lights like you might do on a film set but I prefer to start as simple as I can, early in the process.

Starting with a Skylight to capture the scene and give us ambient light. I also used a Directional light but since my scene was very overcast I gave it a very small value.  The sky is going to play a major role in the overall look and feel of your scene. I created an unlit material with an overcast HDR from HDRI haven mapped to a simple skydome.

SKY_HDR

Knowing that typical Lumince output of an overcast sky is approx 1000-2000 Lux is our target. But how do you measure our luminance is in range? 

 

Using Brian Leulux’s Widget we can convert the Illuminance from the sky and directional light and tweak the lights until we reach our target scene luminance.

 

The steps I took to measure and calibrate the scene’s luminance was as follows:

 

⦁ Place a flat plane with a rough material assigned to it where you’d like to get your reading.

⦁ Start the Pixel Inspector and move your cursor over to the pixels you want to measure.

⦁ Note the luminance value. You can press “Escape” while measuring to lock the value.

⦁ Copy/paste or input the luminance value into the luminance box of the widget and it will generate the illuminance value.

⦁ If that is not near your target value(for instance, a bright clear day around noon can be between 80,000 Lux and 120,000 Lux), then adjust lighting as you like and remeasure.

⦁ You can also work in the opposite direction by inputting your target illuminance and lighting until your luminance in the Pixel Inspector nears the one converted from the illuminance input.

PixelPicker

Secondary Light sources

 

After setting up the main light sources for the scene, I move onto my secondary lights. The desk lamps are just 4  non-shadow casting point lights set to static at 450 Lumens and Light temperature of 2500 Kelvin. I didn’t want the ceiling lamps to contribute much to the overall scene, so I simply had their emissive material contribute to the lightmass bake.

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It’s after this point I adjust my Lightmass settings and dial in my final bake. Here are the settings I used for this scene.

Lightmass_settings
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Pre_grade

Screenshots of final bake before color grading.

Post Processing

 

Now that I have a clean bake that I’m happy with I begin to bring back some of the settings I had previously disabled in my post-processing volume. I added some subtle Bloom, vignetting, and chromatic aberration. 

 

I also applied a rainy glass shader to the windows to help sell the rainy afternoon mood.

Color Grading 

 

In Da Vinci Resolve, I pushed the scene to be cooler and compensated by bringing back the warms in highlights and subtly in the mid-tones.I also desaturated the shadows to achieve a more ‘filmic’ look.  It took a lot of back and forth trying to find a final color treatment I was okay with.

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Post color grading.

I then exported a LUT and brought it back into the Post presses volume before exporting a small video sequence.

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Conclusion 

 

I feel like I’ve only scratch the surface on my understanding of exposure and color grading. Projects like these keep me excited to continue diving deeper into color grading, exposure, and other film and photography concepts to sharpen my skills as a lighting artist.