Data compression or tone curve where input and output don't scale linearly — JPEG, H.264, gamma. Reduces file size while preserving perceived quality.
In the VFX workflow, we encounter nonlinear encoding wherever data is compressed or light values are psychovisually optimized—and each time, we must understand what is lost and what is preserved. Unlike linear encoding, where input and output behave proportionally, nonlinear methods utilize the limits of human perception: the eye reacts to brightness ratios logarithmically, not linearly. JPEG aggressively compresses color information in higher frequency bands because we need less sharpness there. H.264 and its successors work with similar psychovisual models—they deliberately discard information that we don't see.
In practice, this means for us on set and in the edit: nonlinearly encoded footage often looks better immediately—high contrast, saturated—but it is also manipulated. Log-encoded raw footage (like ProRes Log or DCI P3) is the opposite: stored linearly in light information, flat, uncomfortable to watch, but with full flexibility in color grading. Conversely: when we bring JPEG or H.264 material into the VFX edit, we have already lost information that we cannot recover later. This becomes critical when we extract keyframes for compositing or apply color correction to dimly lit areas.
Gamma curves are a classic form of nonlinear encoding—they compress the bright values and expand the dark ones, which looks more natural on monitors with limited dynamic range. But in the VFX backend, we almost always work linearly, thus converting source material to a linear color space first, performing our effects, and only encoding nonlinearly for the final output. This is complex, but unavoidable—otherwise, nonlinear artifacts like banding or color shifts will propagate through all layers.
The practical tip: Know the encoding of your source material. If it's nonlinearly encoded, ask for the RAW or Log variant where possible. And if not possible—JPEG, H.265 from surveillance or older online material—then factor in that you have no latitude in the shadows and must place your keys accordingly with caution.