How good is HD TV
HD TV has a wider TV picture screen compared to an ordinary TV screen. HD TV also has better picture quality than an ordinary TV because the picture is much more sharper and you will not see the net like pattern on the TV screen when you go closer to the HD TV screen.
HD TV image size
The picture here compares an Ordinary TV Vs HDTV picture. HDTV has a width to height ratio of 16:9 compared to a standard definition TV picture width to height ratio of 4:3. The width to height ratio of a TV is known as the aspect ratio. Thus in an HDTV of picture height of say 45 inches the width will be 80 inches. In an standard TV picture of the same height of 45 inches the width will only be 60 inches. So in our example here of a TV picture of same height of 45 inches, since the SDTV and HDTV aspect ratios are different, the SDTV produces a picture of only 60 inches wide compared to 80 inches width of the HDTV. Hence an HDTV picture is one third wider than a standard TV picture of same height.
The main benefit of HDTV over Ordinary TV picture is that the HDTV picture quality is very clear and much better than ordinary TV pictures. When HDTV picture is compared to ordinary TV picture, the HDTV picture quality is crisper and more detailed due to the higher resolution of HDTV. You do not see that grainy sort of picture like on the old ordinary standard definition TVs. HDTV has 1920x1080 pixel resolution compared to old CRT standard television pictures of 640x480 pixels. The wider picture of the HDTV is a pleasure to watch with less eye strain. The Video below explains in detail the difference between ordinary TV and HDTV
Pixel size of HDTV
TV image on the screen of all TVs are made up of tiny squares known as pixels. These tiny square pixels are arranged like a fine net along the width and height of the TV. A Full HD TV image has 1920 pixels arranged left to right on the 'X' axis and 1080 pixels arranged from the bottom to top on the 'Y' axis. This is usually written as 1920x1080 pixels.
Does a bigger HD TV set have more pixels than a smaller HD TV? No, all High Definition HD TVs have the same number of pixels whatever their size. Each of the pixels in a bigger HD TV will be bigger to make exactly 1920 pixels along the width of the screen and 1080 pixels along the height of the screen. You cannot have more pixels than the number of pixels in the HD Video signal. HD Video image signals are in 1920x1080 format and each pixel in the TV screen must match exactly each bit of digital information in the video signals. The 1920x1080 Video image signals can come to the TV from various sources like a DVD player or USB stick or an HD TV broadcast like from Dish TV.
How images appear on TV screen
How an image is formed on the TV screen is explained with the use the figure shown here. The TV screen image is formed by scanning, in which each TV pixel gets the corresponding digital information in the video signal. Each TV pixel in the first row (1) gets corresponding digital information in the video signal starting from the top left corner and going left to right. When the first row scan is over, the scan stars over again from left to right, but one row down in the second row (2). The prcess is repeated till the last row of TV pixels at the very bottom of the TV screen is fed with the video digital signal. When the last row has finished scanning, one complete image frame is formed on the TV screen. The scan now starts again from the top left corner for the next TV image frame (3). There has to be about 60 TV image frames per second to have a smooth movements of images on the TV screen.
Difference between 480p 720p 1080i and 1080p
All these figures 480p 720p 1080i and 1080p refer to the vertical resolution of a TV screen. The figures 480, 720 and 1080 is the number of horizontal lines of pixels in a TV screen and the letters 'p' and 'i' refers to how the image is scanned and appears on the TV screen.
480p was the standard resolution of the old Tube TVs with the picture in the 4:3 aspect ratio. 720p, 1080i and 1080p are the number of horizontal lines in the new wide format flat TVs. HD ready TV has only 720 lines of horizontal resolution while Full HD TV has 1080 lines of horizontal resolution.
The 720 refers to the 'HD ready' TV resolution of 1280x720 pixels where there are 720 lines of horizontal resolution. 1080 refers to the 'Full HD' resolution of 1920x1080 pixels. The video below explains the difference between HD ready and full HD TV.
difference between 1080i and 1080p
The 'p' and 'i' in 480p 720p 1080i and 1080p refers to how the TV image is scanned. The 'p' stands for 'Progressive' and 'i' stands for 'interlaced' TV image.
In the 'p' progressive scan image all of the horizontal lines in a TV image is scanned together at one time and there will be 60 full image frames per second on the TV screen.
For the 'i' interlaced scanning, each of the 60 frames per second are only half images. How interlaced scanning works is explained in the image above. Alternative rows of a TV image are scanned in each frame of the image. Thus in the first scan, rows 1, 3, 5 and all odd rows of the TV image resolution lines are scanned to form one half frame. In the second scan, rows 2, 4, 6 and all the even rows are scanned to form the other half of the image frame. The two frames are then combined to form the complete picture as shown in the image here.