In this video, learn how to set camera exposure to match scene lighting.
- [Instructor] A physically accurate lighting simulation reproduces all possible brightness values visible to the human eye. But the range in values that can be displayed or printed is more limited. For example, current display technology can't reproduce the intensity of sunlight. We need to control the rendering to optimize it for display, mapping a wide range of intensity values to something manageable, and that will fit into the gamut of our display or print medium.
In real-world photography, traditional cameras accomplish this with exposure controls. The sensitivity of the film or sensor, the time that the sensor is exposed to light, and the size of the aperture, or opening, allow the photographer to direct the image brightness and contrast, optimizing exposure in a particular range, such as skin tones or shadows. And so it is with physically-based 3D renderings, we must choose how the raw light data is to be interpreted.
Some 3D applications offer a simulation of a physical camera, with traditional numerical inputs for ISO, exposure time, and f-stop. These controls can be adjusted to tonemap the image, and bring the brightness and contrast into a range suitable for presentation. Here's a composite render showing three different exposures, and the one in the center is optimally exposed. Exposure is measured in exposure value units, we can see that for a bright daylight shot, such as this one, an exposure value of around 14 or 15 will be best.
The other way to tonemap images is in post-production. The 3D renderer saves out raw exposure data, in EXR format, or some other high dynamic range image format. For best results, we should save out at least 16 bits of floating-point data per color channel. Then the image is imported to an image processing, or compositing application, and suitably adjusted for exposure, contrast, tone curve, color palette, and so on.
This is sometimes called color grading or just grading. Post-processing has many advantages, not the least of which is the ability to adjust the image without re-rendering. Raw exposure values are much easier to readjust than an already-tonemapped image. Even if the 3D renderer's tonemapping is useful to you, I recommend always saving out a high dynamic range file as an insurance policy. If you make many changes or wish to derive many variations from a single render, a post-processing workflow is essential to meeting your production goals.
- Choosing a visualization app
- Managing assets
- Shading with materials and textures
- Daylighting, practical lighting, and studio lighting
- Lightbox and macro photography
- Vehicles and large-scale objects
- Architecture and interior design
- Technical illustrations
- Rendering passes and light groups
- Rendering for print, prepress, and broadcast
- Animating turntables and orbits
- Rigging and animating a walkthrough