Capture technique recording luminance data across multiple exposures — merged into environment maps in post. Essential for photorealistic VFX integration and real-time rendering.
For your VFX shots, you need an environment map that not only looks like the real world but also fully captures the light space — this is precisely what the principle of multiple exposures achieves. Instead of taking a single shot, you photograph the same scene with different shutter and aperture settings: one for the highlights, one for the midtones, one for the shadows. This series of exposures is then combined in post-production, allowing you to retain detail information in both the extreme highlights and the deep shadows — this is the core of the process.
The practical benefit is obvious: if you want to composite a 3D character or object into a real background, the light hitting your render geometry must precisely match the light of the recording scene. A standard JPEG or 8-bit capture cannot store all the information — it clips highlights and loses shadow details. With multiple exposures and their subsequent combination into a 32-bit or higher compressed format (often .exr or .hdr), you have a complete radiometric dataset. Your rendering engine — whether Arnold, RenderMan, or V-Ray — can then use this as a lighting source, and the CG object will appear natural in the scene.
On set itself: a tripod is mandatory, the camera in manual mode, ISO fixed (usually 400–800), aperture fixed (f/8–f/11 depending on daylight). You expose in increments — typically EV±2 or EV±3 — and take 5 to 7 shots in quick succession. Movement in the scene is your enemy; with moving water or trees, you'll need to align manually later or shoot multiple sets at different times. RAW format is standard because you need maximum flexibility in post.
In post-production, these exposure series are calculated together using tone-mapping software (Photoshop with plug-ins, Luminance HDR, or proprietary pipelines). The result is a radiance map — a textured sphere containing 360° ambient light. This is then integrated into the rendering, often additionally separated into diffuse and specular passes for more control in the comp.