Graph showing how a camera translates input light into digital values — defines contrast behavior, gamma, and highlight rolloff. Every sensor has its own curve.
Characteristic Curve
The characteristic curve describes how your camera converts incident light into digital signal values. Instead of working linearly — input doubles, output doubles — each model follows an individual curve that critically determines the image's appearance. You see this immediately in the raw format: the red Epic has a different gradation than the Alexa, which in turn compresses differently than the FX30. These differences are not flaws, but intentional designs.
Practically, you notice this when setting shadows and highlights. A characteristic curve with a steep mid-range provides contrast in the normal image area but flattens out at the extremes — exactly the rolloff behavior that makes highlights appear "soft." Conversely, a flat curve across the entire range compresses contrast and gives you maximum correction latitude in color and exposure (as with S-Log or Venice Log format). On set, you notice this during exposure: with linear sensors, you have to be more precise, while with logarithmic ones, you have up to 14 stops of leeway, but at the cost of a muted look in RAW.
The characteristic curve directly influences your exposure strategy. If you prefer fast, high-contrast looks (e.g., for comedy or action), you work with gamma curves that lift the midtones. If you need maximum gradeability (documentary, VFX-heavy), you choose log formats — the characteristic curve then drops off flat over ten to fourteen stops. The LUT is then your tool to bring the curve back into display space later. Every monitor, every projector profile also has a characteristic curve — which is why what you see on set doesn't always match the final DCP.
In editing and color correction, you constantly work against or with the characteristic curve. Curves and levels are nothing more than characteristic curve edits. If the original camera characteristic curve was too harsh on the highlights, you pull down there. If you need more contrast in log material, you add an S-curve on top. That's why it's crucial for a DoP to know their camera's characteristic curve — and to communicate to the colorist later what characteristics you shot with. This saves hours in the grading suite.