Questions

The basics

What is HDTV?
HDTV stands for high-definition television. It is a digital broadcasting system with greater resolution than traditional television systems.
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What is SDTV?
SDTV stands for standard-definition television. This usually refers to digital television (the signal) but is in similar resolutions to analog television.
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What is EDTV?
EDTV stands for enhanced-definition television. This refers to digital television that is better than SDTV but not quite HDTV.
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So what is the real difference between HDTV, SDTV, and EDTV and how are they different than analog TV?
HDTV, SDTV, and EDTV all refer to the use of digital content, this is the main difference to analog TV. HDTV, SDTV, and EDTV use digital transimission (zeros and ones) to send the video data which used with compression allows more data to be sent. This translates into more lines being sent. Analog TV has limitations on the amount of data that can be sent, thus limiting the amount of lines being sent, leading to a lower resolution as compared to HDTV. SDTV, though being digital, can have the same number of lines (the same resolution) as analog TV, but may seem to be clearer as there may be a lack of ghosting, static, or snowy imagery. SDTV does not have these defects but may have other artifacts such as blockiness or stuttering.
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What are these resolutions that we keep hearing about and how do they relate to HDTV, SDTV, and EDTV?
HDTV can be broadcast in multiple resolutions. The ones you hear about most often are referred to as 1080p (HD-DVD, BluRay), 1080i, and 720p. 1080 resolves to a resolution of 1920x1080 where the p and the i refer to progressive and interlaced respectively. 720 resolves to a resolution of 1366x768. SDTV can is broadcast at a resolution of 720x480 and is refered to as 480i. EDTV is broadcast at 704x480 but is broadcast using progressive scanning. The formats in order of higher to lower resolution are 1080p, 1080i, 720p, 480p, 480i.
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