What Is EOTF?

EOTF stands for Electro-Optical Transfer Function. It is a technical term in display engineering and video production that describes how digital signal values (electrical input) are converted into visible brightness (optical output) on a screen.

Why Is EOTF Important?

Before EOTF, video standards used a “gamma curve” to translate digital signals to light output. With the rise of HDR (High Dynamic Range) content, new EOTFs were developed to handle a wider range of brightness and more accurate color reproduction.

EOTF defines how a display should render brightness, contrast, and detail from the signal it receives. This ensures content looks the same on different devices, as intended by the creator.

Types of EOTF

• Gamma 2.2 / 2.4 – Used in SDR (Standard Dynamic Range) displays.
• PQ (Perceptual Quantizer) – Used for HDR10 and Dolby Vision. Designed to match human vision, allowing for much higher peak brightness and more detail in shadows and highlights.
• HLG (Hybrid Log-Gamma) – Used mainly for HDR broadcast TV. Compatible with both SDR and HDR displays.

Real-World Example

As a display engineer, I’ve seen EOTF play a crucial role in HDR TV calibration. For example, if a TV is set to the wrong EOTF (using a gamma curve for HDR content), the images will look too dark or washed out, losing the intended impact of HDR. Correct EOTF ensures accurate reproduction of movies, games, and live broadcasts.

Recommendation

If you want the most accurate and vibrant viewing experience, make sure your display and source devices are set to the correct EOTF for the content (HDR or SDR). This will preserve the creator’s intent and ensure all details, colors, and brightness are displayed faithfully.

References

BBC: HLG EOTF Explanation