Over the years, the PC and TV industries have developed a number of screen formats, each one increasing in resolution, as technology advanced. Projectors and many TV sets nowadays provide the added functionality to accept PC signals and display PC formats. Video scaling technology has resulted in the capability to scale video formats to lower or higher resolutions. Therefore a 1080i signal may not be displayed at 1080i resolution. The multiplicity of formats and the ability to scale formats have resulted in much confusion. For example, what is the difference between XGA and SXGA? What resolutions do they represent? My projector's native resolution is 1365 by 1024 pixels, but it can display 1080i which is 1920 by 1080 pixels. Does this make my projector a 1080i projector? What is native resolution? What is video scaling? This simple guide to video formats helps to answer these questions. Some simplification is involved, as we do not want to get lost in too many details. More information can be found on the internet, using key words introduced in this guide.
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The basic PC graphics video format is VGA, which stands for Video Graphics Array, introduced by IBM in 1987. Prior to this, IBM introduced CGA (Color Graphics Adapter) in 1981 which had a resolution of 640x200 pixels, followed by EGA (Enhanced Graphics Adapter) in 1984 with a resolution of 640x350. CGA and EGA are now obsolete. With improving technology, PC monitor resolutions have increased from VGA to SVGA, XGA, SXGA, UXGA, QXGA, etc. These will be discussed later. Following the early TV screens, most PC monitors have a 4:3 aspect ratio. However, each 4:3 format has a sister widescreen (16:9) format, which is meant for widescreen TVs or projectors. Nowadays, PC monitors also have widescreen formats. For some special applications, a 5:4 aspect ratio has been developed. The sister widescreen formats are designated WVGA, WSVGA, WXGA, WSXGA, WUXGA, WQXGA, etc. We shall discuss these further later.
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TV formats are the NTSC, PAL or SECAM format. We shall focus on NTSC (National Television Standards Committee), which has a standard format of 648x486. The format allows for pixels at the edges to be neatly cut off to get a 640x480 display. (There are other NTSC formats, but again for simplification, we shall ignore them). NTSC TV has 525 lines, but there are 45 blank lines at the bottom to allow time for the TV to receive the next frame before scanning starts at the top line again. Thus only 480 lines are displayed. With the advent of digital TV, the ATSC (Advanced Television Systems Committee) has defined SDTV (Standard Definition Television) to be 480i (the i stands for interlaced) which is 640x480 resolution. The ATSC has also defined EDTV (Enhanced Definition Television) to be 480p (the p stands for progressive scanned) which is also 640x480 resolution, but the progressive scan enhances the resolution as perceived by the eye.
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Interlaced video first displays the even numbered lines of the frame (with blank lines in-between) which takes 1/60 seconds to scan, followed by the odd numbered lines of the frame (with blank lines in-between). Thus each full frame takes 1/30 seconds to display, and the frame rate is thus 30 frames per second. This method is used to reduce the bandwidth of the television transmission. Progressive scan technology recombines all the lines of the frame before displaying the full frame which also takes 1/60 seconds to scan. Thus the frame rate is 60 frames per second. The lack of blank lines and the higher frame rate give a perception of higher resolution and much reduced flicker although the picture is still 640 pixels by 480 pixels. The widescreen (16:9 aspect ratio) version of 480p is a resolution of 854x480. With the advent of high definition television (HDTV), ATSC defined 720p at 16:9 aspect ratio to be 1280x720 resolution, and 1080i or 1080p at 16:9 aspect ratio to be 1920x1080 resolution.