Scan rate
Posted: Mon May 03, 2004 9:21 pm
Scan rate describes the amount of available resolution in a video signal and also determines the frequency or speed of the signal. The higher the number the faster the display must work to create the image at that rate or speed (a concern of old CRT displays). The following are scan rates that have been used for consumer video entertainment products.
240p = 640X240 - old NTSC display based video game consoles
480i = 640X480 - standard definition television, NTSC
480p = 640X480 4:3 or 720X480 16:9 - SD DVD
540p = 1920X540 - used for external scaling only to old CRT interlaced displays
720p = 1280X720 - native HDTV
1080i = 1920X1080 - native HDTV
1080p = 1920X1080 - HDTV* and native HD Disc - Blu-ray and HD DVD
*the ATSC table supports 1080p24 and 1080p30, 24 and 30 frame video, but no one is broadcasting either scan rate
The i stands for interlaced and the p for progressive. Progressive is preferred over interlaced because complete frames are shown. Interlaced is a form of analog compression that splits the frame into two fields causing picture artifacts and lower resolution when the image is in motion but higher resolution when the image is still.
In the past we had only NTSC video which uses 480i and comes in a variety of different connections and level of performance. Our displays have been 480i also and this is called the native scan rate. HDTV displays though are 720p, 1080i, or 1080p and that means your HDTV has one of these native scan rates and possibly one more, 480p (CRT only). There are few displays that do more than two (CRT only). Connecting a 480i signal to a native 480i display is a straight forward process. Connecting that signal to an HDTV will not work until it has been converted to the native scan rate of the display. This process is called scaling and every HDTV has one that will convert most everything out there so you can view it on the display. We call this an internal scaler. Int he early days all the internal scalers were quite poor degrading the final image you see. Today things have greatly improved for the casual viewer but videophiles may still opt for external scaling. The way to get a performance edge is to use an external scaler that does a far better job and set it to the native scan rates of your display.
The key to scan rate is to remember that your display looks the best when you feed it the one that is native to the display. If your display is native 720p then it will look it
240p = 640X240 - old NTSC display based video game consoles
480i = 640X480 - standard definition television, NTSC
480p = 640X480 4:3 or 720X480 16:9 - SD DVD
540p = 1920X540 - used for external scaling only to old CRT interlaced displays
720p = 1280X720 - native HDTV
1080i = 1920X1080 - native HDTV
1080p = 1920X1080 - HDTV* and native HD Disc - Blu-ray and HD DVD
*the ATSC table supports 1080p24 and 1080p30, 24 and 30 frame video, but no one is broadcasting either scan rate
The i stands for interlaced and the p for progressive. Progressive is preferred over interlaced because complete frames are shown. Interlaced is a form of analog compression that splits the frame into two fields causing picture artifacts and lower resolution when the image is in motion but higher resolution when the image is still.
In the past we had only NTSC video which uses 480i and comes in a variety of different connections and level of performance. Our displays have been 480i also and this is called the native scan rate. HDTV displays though are 720p, 1080i, or 1080p and that means your HDTV has one of these native scan rates and possibly one more, 480p (CRT only). There are few displays that do more than two (CRT only). Connecting a 480i signal to a native 480i display is a straight forward process. Connecting that signal to an HDTV will not work until it has been converted to the native scan rate of the display. This process is called scaling and every HDTV has one that will convert most everything out there so you can view it on the display. We call this an internal scaler. Int he early days all the internal scalers were quite poor degrading the final image you see. Today things have greatly improved for the casual viewer but videophiles may still opt for external scaling. The way to get a performance edge is to use an external scaler that does a far better job and set it to the native scan rates of your display.
The key to scan rate is to remember that your display looks the best when you feed it the one that is native to the display. If your display is native 720p then it will look it