Sampling rate
Posted: Sun Jul 24, 2005 11:35 am
This refers to the following expression.
4:4:4
4:4:2
4:2:2
The first number represents the green channel of an RGB signal which in most cases is the final form used to drive a particular display technology. It always represents the highest sampling rate of the system. The second and third numbers represent red and blue.
In the case of RGB the sampling rate is always 4:4:4 because RGB is exactly that, all three colors fully expressed with video and color information. This is normally used in mastering and production prior to final encoding for consumer use.
4:4:2 means that red is sampled at the same rate of green. This is used because red is a primary color which we can easily perceive detail in unlike blue. Typically this is reserved for production applications. The blue is represented by 2 which means blue is sampled at half the rate. Using 1920 X1080 as an example green and red are fully capable of sampling and reproducing 1920 vertical lines or pixels horizontally. Blue is limited to half of that or 960 lines. Blue is more of a color perception related product than detail so this conversion is considered acceptable depending on the application.
4:2:2 means that both red and blue are sampled at half the rate. This is what is used for consumer delivery of video whether it be Blu-ray DVD movies. Using the prior example of 1920X1080 the final result is the black and white portion of the image can sample and reproduce 1920 vertical lines or pixels horizontally. The color on the other hand is limited to half of that or 960 lines for all three color primaries red, green and blue.
4:2:0 means that red is sampled at half the rate and blue is sampled at a 1/4 the rate. This is used by the DTV system for any video content including HD. You still get 1920x1080 for the black and white image and a 960 line color response for red and green but blue color is limited to 480 lines. Blue is not a detail color and that is why this compression is considered acceptable.
These numbers can also reflect digital video levels.
4:4:4
4:4:2
4:2:2
The first number represents the green channel of an RGB signal which in most cases is the final form used to drive a particular display technology. It always represents the highest sampling rate of the system. The second and third numbers represent red and blue.
In the case of RGB the sampling rate is always 4:4:4 because RGB is exactly that, all three colors fully expressed with video and color information. This is normally used in mastering and production prior to final encoding for consumer use.
4:4:2 means that red is sampled at the same rate of green. This is used because red is a primary color which we can easily perceive detail in unlike blue. Typically this is reserved for production applications. The blue is represented by 2 which means blue is sampled at half the rate. Using 1920 X1080 as an example green and red are fully capable of sampling and reproducing 1920 vertical lines or pixels horizontally. Blue is limited to half of that or 960 lines. Blue is more of a color perception related product than detail so this conversion is considered acceptable depending on the application.
4:2:2 means that both red and blue are sampled at half the rate. This is what is used for consumer delivery of video whether it be Blu-ray DVD movies. Using the prior example of 1920X1080 the final result is the black and white portion of the image can sample and reproduce 1920 vertical lines or pixels horizontally. The color on the other hand is limited to half of that or 960 lines for all three color primaries red, green and blue.
4:2:0 means that red is sampled at half the rate and blue is sampled at a 1/4 the rate. This is used by the DTV system for any video content including HD. You still get 1920x1080 for the black and white image and a 960 line color response for red and green but blue color is limited to 480 lines. Blue is not a detail color and that is why this compression is considered acceptable.
These numbers can also reflect digital video levels.