Majority of LCD TVs are HDTVs. But, some of the sets smaller screens will not be. The following shows how you can determine this.
An HDTV or HDTV-compatible TV will have a vertical resolution of a minimum of 720 lines. These lines are depicted as a 1280×720 pixel field, that is, 1280 pixels from the left of the screen to the right and 720 pixels from top to bottom. Smaller LCD TV sets are referred to as EDTVs (Extended or Enhanced Definition TVs) since they only have a resolution lower than 720 lines.
EDTVs normally have a native pixel resolution of 852×480 or lower. 852×480 refers to 852 pixels across the screen and 480 pixels down the screen. 480 also indicates the number of lines from the top of the screen to the bottom. This resolution is higher than standard TVs, but lesser than HDTVs.
The image quality on these sets is quite good, particularly while viewing DVDs and standard digital cable transmissions, but not comparable with that of HDTVs. LCD TVs that can directly display HDTV signals have a native pixel resolution of 1280×720 or higher.
LCD TVs have a limited number of pixels (hence, they are called fixed-pixel displays). So, input signals with higher resolutions would require scaling to match the pixel field count of a specific LCD. For instance, a HDTV input format of 1080i requires a native pixel resolution of 1920×1080 for a one-on-one point display of the HDTV image.
But, if your LCD TV has a resolution of only 852×480 or 1024×768, the incoming HDTV signal requires scaling down to match the pixel count on the surface of your LCD screen. Thus, input HDTV signals always need scaling down to match the native pixel field of the LCD TV.
Thus, while purchasing an LCD TV, do verify whether the unit is an EDTV or is HDTV-ready. At present, almost all LCD TVs, with screens 23 inches and above, are compatible with HDTVs. In addition, most have a native pixel resolution of 1280×720, 1366×768, or higher (1080p). However, some of the smaller units (with screen sizes lesser than 20 inches) are usually not HDTV-ready.