Standard-dynamic-range video

Standard-dynamic-range video (SDR video) refers to video having a traditional range of luminance levels, as opposed to the wider range offered by high-dynamic-range video (HDR video). SDR video is limited in its ability to represent a wide range of light intensities, from very dark to very bright scenes. This limitation is due to its reliance on a gamma curve that has been the standard in broadcasting, digital cinema, and home cinema for many years. The dynamic range in SDR video is typically around 6 to 9 stops of light, whereas HDR video aims to represent up to 14 stops or more.

Definition and Characteristics

SDR video uses a gamma curve that is based on the CRT (Cathode Ray Tube) displays' characteristics, which were standard before the advent of flat-panel technologies like LCD, LED, and OLED. The gamma curve helps in optimizing the use of bit depths in digital video signals, ensuring that the luminance levels are distributed in a way that is more in line with human vision's non-linear response to light. However, this curve limits the maximum brightness and color depth that can be displayed, resulting in a narrower dynamic range compared to HDR video.

Technical Specifications

The most common color space for SDR video is Rec. 709, which was standardized by the ITU (International Telecommunication Union) for HDTV broadcasting. Rec. 709 specifies a color gamut, gamma curve, and white point, among other parameters. SDR video typically uses 8-bit color depth, allowing for up to 16.7 million colors. The peak brightness for SDR content is usually around 100 nits, significantly lower than the 1000 nits or more that HDR content can display.

Comparison with HDR Video

The primary difference between SDR and HDR video is the dynamic range, which refers to the contrast between the darkest and brightest parts of an image. HDR video can display a wider range of luminance levels, allowing for more detailed shadows, brighter highlights, and a broader color spectrum. This results in a more lifelike and immersive viewing experience. HDR technologies, such as Dolby Vision and HDR10, use dynamic metadata and 10-bit or higher color depth to achieve these improvements over SDR video.

Applications and Content

SDR video remains prevalent in many applications, including standard-definition television (SDTV), high-definition television (HDTV), DVDs, and some streaming services. Despite the growing availability of HDR content, SDR is still widely used due to its compatibility with existing infrastructure and the vast majority of existing content libraries.

Future Outlook

As display technologies continue to evolve, the adoption of HDR video is increasing. However, SDR video will likely remain in use for specific applications and legacy content. The transition to HDR is gradual, with content creators, broadcasters, and technology providers balancing the benefits of HDR against the costs and technical challenges of production, distribution, and display.