When you sit down and watch your favorite program or movie on your TV or video projector, you see what appears to be a series of complete images, like a photograph or film. However, appearances are deceiving. If you actually get your eyes close to a TV or projection screen, you will see that it is made up of little dots that are lined up in horizontal and vertical rows across and up and down the screen surface.
A good analogy is a common newspaper. When we read it, it looks like we are seeing single images and letters, but if you look closely, or get a magnifying glass you will see that those letters and images are made up of tiny dots.
The Pixel Defined
The dots on a TV, video projection screen, PC monitor, laptop, or even tablet and smartphone screens, are referred to as pixels.
A pixel is defined as a picture element. Each pixel contains red, green, and blue color information (referred to as subpixels). The number of pixels that can be displayed on a screen determines the resolution of the displayed images.
To display a specific screen resolution, a predetermined number of pixels has to run across the screen horizontally and up and down the screen vertically, arranged in rows and columns.
To determine the total number of pixels covering the entire screen surface, you multiply the number of horizontal pixels in one row with the number of vertical pixels in one column. This total is referred to as pixel density.
Examples of the Resolution/Pixel Density Relationship
Here are some examples of Pixel Density for commonly displayed resolutions in today’s TVs (LCD, Plasma, OLED) and video projectors (LCD, DLP):
480i/p represents 740 horizontal x 480 vertical pixels = 345,600 total pixels.
720p represents 1,280 horizontal x 720 vertical pixels = 921,600 total pixels.
768p represents 1,366 horizontal and 768 vertical pixels = 1,049,088 total pixels.
1080i/1080p represents 1,920 horizontal x 1080 vertical pixels = 2,073,600 total pixels.
4K (Consumer Standard) represents 3,840 horizontal x 2,160 vertical pixels = 8,294,400 total pixels.
4K (Cinema Standard) represents 4,096 horizontal x 2,160 vertical pixels = 8,847,360 total pixels.
8K represents 7,680 horizontal x 4,320 vertical pixels = 33,177,600 total pixels
Pixel Density and Screen Size
In addition to pixel density (resolution), there is another factor to take into consideration: the size of the screen that is displaying the pixels.
The main thing to point out is that regardless of the actual screen size, the horizontal/vertical pixel count and pixel density does not change for a specific resolution. In other words, if you have a 1080p TV, there are always 1,920 pixels running across the screen horizontally, per row, and 1,080 pixels running up and down the screen vertically, per column. This results in a pixel density of about 2.1 million.
In other words, a 32-inch TV that displays 1080p resolution has the same number of pixels as a 55-inch 1080p TV. The same thing applies to video projectors. A 1080p video projector will display the same number of pixels on an 80 or 200-inch screen.
Pixels per Inch
However, even though the number of pixels stays constant for a specific pixel density across all screen sizes, what does change is the number of pixels-per-inch. In other words, as the screen size gets larger, the individually displayed pixels have to also be larger in order to fill the screen with the correct number of pixels for a particular resolution. You can actually calculate the number of pixels per inch for specific resolution/screen size relationships.
TVs vs Video Projectors
It is also important to note that with video projectors, the displayed pixels per inch for a specific projector can vary depending on the size screen used. In other words, unlike TVs which have static screen sizes (in other words, as 50-inch TV is always a 50-inch TV), video projectors can display images in a wide variety of screen sizes, depending on the projector’s lens design and the distance the projector is placed from a screen or wall.
In addition, with 4K projectors, there are different methods on how images are displayed on a screen that also affects the screen size, pixel density, and pixels per inch relationship.
The Bottom Line
Although pixels are the foundation of how a TV image is put together, there are other things that are required to see good quality TV or video projector images, such as color, contrast, and brightness. Just because you have a lot of pixels, doesn’t automatically mean you will see the best possible image on your TV or video projector.