Specifications that determine the quality of TV picture
Before buying a TV you should have a clear understanding of all the important TV specifications that relate to the picture quality of a TV. On this page we list and explain each of specs that makes a TV picture good or bad.
There are several factors which make a flat TV picture quality good or bad. These most important TV Specs with regard to the picture quality of a flat TV are listed below. A clear explanation of what each TV picture quality spec means is given. Each item in the list below is a clickable link which will take you down directly to the detailed explanation of that subject concerning a flat screen TV picture.
- TV Pixels explained
- Meaning of TV Resolution
- How do images appear on TV screen
- What does i and p mean in 1080i or p, Progressive and Interlaced Scan
- Telecine Pulldown
- What 'Hz' means in TV specs
- What is meaning of Contrast Ratio in TV
- HD Ready vs Full HD TV
- 4K Ultra HD TV explained
TV Pixels explained
The picture on a TV is made up of thousands of tiny dots known as Pixels as shown on the left. A pixel is the short form of ‘Picture Element’ where the ‘Pix’ stands for 'picture element'. A Pixel is the smallest element which goes to make the picture on the TV. If you go close up to any television you should be able to see the pixels similar to the picture on the left. The more the number of pixels to make a TV picture the sharper it becomes. In HDTV these pixels are barely visible and you must go really close up to see them.
Resolution theoretically should be defined as the number of pixels per unit of measurement or the TV Pixel Density expressed as PPI (Pixels Per Inch) as is being done on mobile phone screens. For TV the resolution is fixed and is expressed by the total number of pixels horizontally by the number of pixels vertically, for example HDTV is expressed as 1980x1080 or Ultra HDTV or UHDTV can go up to 7,680×4,320 pixels.
TV Resolution meaning explained
The picture below shows a grid diagram (not to scale) or graphical representation of pixels on TVs of different resolutions
In the picture below it will be noticed that the grid lines get closer together in a higher resolution display. Exactly like the grid lines in the picture below, a higher resolution TV pushes the pixels closer together to give a sharper picture.
How do images appear on TV screen
How is the picture formed on the TV screen? In a very simplified way, we can explain how a picture is formed on a TV by the use of the picture on the right. In a CRT television the picture on the TV screen gets "painted" on the screen like this.
An electron beam "paints" the image on the screen by moving from left to right starting from the top left hand corner (1). When it reaches the other end of the screen the beam offs and quickly moves back to the left side (2) and at the same time going down a little bit. It repeats this process till it finally reaches the bottom right hand corner. Now the beam has painted one frame of the TV picture on the TV screen. The electron beam offs and then moves back up and repeats the process (3). All of this is done in fractions of a second, since the beam has to paint about 24 full pictures on the screen per second. As the beam paints each line from left to right, the intensity and characteristics of the beam is changed to create different shades of colors across the screen.
There are currently four standard resolutions for the number of horizontal lines. In the old CRT TV it was 480 lines. The HD Ready and the ordinary DVD players have 720 lines. HDTV and Blu-Ray DVD players have 1080 lines and ultra HDTV has 2160 lines.
What does i and p mean in 1080i or p, Progressive and Interlaced Scan
TV transmission companies, in order to reduce the Bandwidth required to transmit TV pictures, devised a method by which each frame of a picture is split into 2. The odd lines starting from the top, that is line 1, line 3, line 5, etc are made into one frame. Similarly the even lines 2, 4, 6, 8, etc are made into the second frame. This means that the TV transmitting station only has to transmit half the picture information or data at a time, even though they have to transmit twice the number of pictures in a second, but the info in each frame is less and thus the bandwidth required for transmission is less. This method of transmitting is called 'Interlaced Scanning'. Thus the 'i' after the horizontal line numbers means that it is an interlaced signal like 1080i.
Progressive Scan on the other hand transmits the complete picture at the same time. The 'p' after the horizontal line numbers means that it is a progressive signal like 1080p.
Of the two scanning methods, the Progressive Scan is the better one, because it avoids problems like 'judder' or 'jitter' or 'flickering' in the TV full picture when the 2 interlaced pictures are combined. So in effect the best quality picture from today's TV technology is available from a 1080p device. Only in a few countries is 1080p transmission available. Blu-ray DVD sends pictures to the TV as 1080p.
Movie Films are recorded at a frame rate of 24 frames per second. Television on the other hand is transmitted at 30 or 25 full frames per second. In the US NTSC transmission system they transmit at 30 full frames per second or 60 half interlaced frames per second. The difference in the frame rates causes a problem to show film movies on TV because of the different frame rates which causes problems like judder or flickering. The conversion from 24 frames of the original cinema to 30 frames for NTSC TV transmission means the frame rates have to be synchronized using technique called 'TeleCine' to transfer film frames to video frames using a process called pull-down. For NTSC the 3:2 pulldown technique and for PAL, which transmits at 25 full frames per second, the 2:2 pulldown technique is used. To achieve perfect match with the TV, it is preferable that the frame rate of the TV are in perfect multiples of 24 - that is 24, 48, 72, 96, 120 and so on. TVs with such perfect multiple refresh rates can show movies better than others. Terms like '24p True Cinema', '24p Real Cinema', etc refer to TV having this feature of playing movies in either 24 frames per second or in perfect multiples of it.
What is Hz in TV specs
‘Hz’ is a symbol for 'Hertz' and is a measurement of frequency, the number of cycles per second. For example AC electricity is at 60Hz or cycles per second in the US and it is 50 HZ in the UK and India.
In a TV the 'Hz' is the Refresh rate per second or the number of times per second, the electron beam paints a frame on the TV screen. Thus for example 60 Hz vs 120 Hz means 60 frames per second vs 120 frames per second. Normal TV stations transmit their signals at 50 or 60 Hz. Higher refresh rate helps in reducing the motion blur on fast moving scenes, like the football looks blurred on the TV when it is moving fast. Obviously the best refresh rate or Hz for a TV will be the higher number, but there is maximum limit that human eyes distinguish.
The frame rate is different from the scan rate. The frame rate is the number of time a different new picture appears on the screen per second. The refresh rate is the number of times per second, the scanning electron beam paints from top to bottom. These numbers can be different, since while refreshing, the same picture can be shown again and again. For example if the frame rate is 30 per second and the refresh rate is 90 per second, then each picture of a frame will be shown repeatedly 3 times while refreshing.
Higher refresh rates were introduced to reduce eye strain due to flickering of the picture in the old CRT TV. On the newer TV they are used to make fast action scenes to appear smoother and not to cause blur, 'Judder' or 'flickering’.
What is meaning of Contrast Ratio in TV, Contrast Ratio vs Dynamic Contrast Ratio
The bigger the Contrast Ratio for TV the better it is. As an example a TV with a contrast ratio of 6,000:1 is better than TV with a contrast Ratio of 3000:1. The meaning of Contrast Ratio in TV is explained as the ratio of the screen's maximum brightness in the whitest area to the brightness in the darkest area or blacks on the screen. If there is absolutely no light in the darkest black of the TV picture then there is zero lumens or brightness there and the value for brightness will be zero. Since any number divided by zero gives an answer of infinity, so the theoretical contrast ratio will be infinity or larger than the largest number. But in actual practice some light bleeds into the darkest area from the bright areas of the screen but the aim of manufacturers is to keep it as small as possible. Thus the contrast values quoted by manufacturers are large, sometimes in the millions.
There two types of Contrast Ratios - Static Contrast Ratio and Dynamic Contrast Ratio. Static Contrast Ratio, as explained above, is the ratio between the whitest white and blackest black that the TV can display. Dynamic contrast ratio is a feature built in the TV, which automatically adjusts the contrast and brightness based on the darkness of the image. To improve the Contrast Ratio of LCD and LED TVs, the backlight of these TV is dynamically adjusted to match the brightness or darkness of the picture playing on the LCD or LED TV. LCD and LED TVs have backlit LCD screen, and for a black object to be shown on screen, the backlight to those LCD elements has to shut off. But for most LCD and LED TVs, all the backlight are on and some light escapes through the LCD element and reaches the screen. Since there is some light falling on the black objects on the screen, the Contrast Ratio of an LCD and LED TVs are less than that of a Plasma TV. This is because Plasma elements light up pixel by pixel, and there is no need to have backlight illumination. Modern LCD TVs, with many innovations have improved their contrast ratio to a very high level and the pictures are great now, almost as good as that of the Plasma TV.
It should be mentioned here that there are no industry standards for Contrast Ratio, and the figures quoted by manufacturers are not a reliable scale for comparison of the Contrast Ratio. To add to this confusion, there two types of Contrast Ratios - Static and Dynamic Contrast Ratio. So if you have to compare Contrast Ratio of different TV models, then a reliable comparison can only be made with models from the same manufacturer - Sony to Sony, Samsung to Samsung, LG to LG, and so on.
HD Ready vs Full HD TV
Full HDTV has 1920 horizontal and 1080vertical pixels (1920x1080). This is called the Native Resolution of the TV and is commonly written as 1920x1080. The 1080 is the number of pixels top to bottom, and it is also known as the number of scanning lines to form the picture on the TV. HD Ready TV has resolution of only 1280x720 or 1,366x768. In Digital Camera talk, the full screen in an HDTV will have 2.07 Million or Mega Pixels. For HDTV ready TV it will only have 0.92 Mega Pixels. Thus you can imagine the difference in image quality of HD Ready vs Full HD TV. We have a sample picture for your comparison at the top of this page.
The term 'HD ready' was introduced by 'The European Industry Association for Information Systems' (EICTA). 'HD ready' means the TV has the minimum screen resolution (at least 1280x720) and digital sockets (HDMI or DVI) to receive and display an HD picture. HD ready is not a High Definition TV, but it can play HDTV to give a picture quality that is near the quality of HDTV. When you want to buy a full HD-TV, make sure that the 'Native Resolution' of the TV is 1920x1080. Also for an HD ready TV the minimum viewing distance is more than that for an HDTV.
4K Ultra HD TV explained
4K Ultra HD TV screen has 3840 pixels horizontally from left to right and 2160 pixels top to bottom. This makes a total of 8.3 Megapixels which is four times the 2.1 megapixels in a full HD TV. So the picture quality in a 4K Ultra HDTV is far better than any full HD TV.
The Ultra HD TV is called a 4K TV because it has 3840 pixels horizontally and since it is almost 4000 pixels or 4K pixels, it got the name 4K TV.