Standard definition (SD)
What is standard definition?
Standard definition (SD) refers to a degree of image or video resolution that was widely used before the advent of high-definition (HD) and ultra-high-definition (UHD) technologies. The specific resolution can vary depending on the aspect ratio, but for a traditional 4:3 aspect ratio, standard definition typically refers to a resolution of 640 pixels by 480 pixels (640x480).
In the context of broadcast television, however, standard definition often refers to a resolution of 720 pixels by 576 pixels in some places, or 720 pixels by 480 pixels in other areas. These resolutions are often referred to as 576i and 480i, respectively.
The history of standard definition
The initial standard definition television (SDTV) systems were based on analog signals, with the resolution determined by the number of lines of image displayed on the screen. The first SDTV systems typically used 525 or 625 lines, corresponding to the 480i and 576i resolutions mentioned earlier.
As digital technology became widely available in the 1990s, standard definition television made the transition from analog to digital. This transition improved image quality, reduced signal interference, and had the ability to support additional features such as multiple audio tracks and interactive services.
Even with these improvements, the resolution of standard definition television remained the same. This is because the resolution is fundamentally limited by the number of pixels that can be displayed on the screen. Increasing the resolution would require many changes in the broadcasting infrastructure.
Standard definition vs. high definition
As high-definition television (HDTV) began taking over in the early 2000s, standard definition was increasingly phased out in favor of the higher-resolution format. High-definition television offers a much better image resolution of up to 1920 pixels by 1080 pixels for 1080i (interlaced) and 1080p (progressive scan) broadcasts.
Despite the superior image quality of high-definition television, standard definition still has its place. For example, many older television shows and movies were originally recorded in standard definition and aren’t as compatible with higher resolutions. Additionally, standard definition requires less bandwidth than high definition, meaning that it’s less taxing for broadcasters and internet service providers.
Is standard definition still relevant?
While standard definition is no longer the cutting-edge technology it once was, it is far from obsolete. Many television broadcasters still offer standard definition channels, particularly for older content that was originally produced in standard definition.
Standard definition is still an option for most video streaming services for slow internet connections too. If there is limited bandwidth or an unreliable connection, it’s often still possible to watch videos in standard definition. While the video resolution is noticeably lower, standard definition reduces interruptions and buffering issues that would be more prevalent for high-resolution video streaming.