What is Chroma Subsampling?
Chroma subsampling is a technique used in video encoding and compression that reduces the amount of data required to represent a color image. It achieves this by reducing the spatial resolution of the color information in the image, while keeping the spatial resolution of the luminance (brightness) information high. This results in a smaller data size for the image, which is beneficial for video streaming applications where bandwidth is limited.
There are several types of chroma subsampling that are commonly used in video encoding.
Types of Chroma Subsampling
4:4:4 Chroma Subsampling
This type of chroma subsampling maintains the full resolution of the color information in the image. The name 4:4:4 indicates that there are four samples for each pixel in the image for both the luminance and chrominance information. This results in a very high-quality image, but it requires a large amount of data to represent it.
4:2:2 Chroma Subsampling
In 4:2:2 chroma subsampling, the chrominance information is sampled at half the rate of the luminance information. This means that for every two luminance samples, there is only one chrominance sample. The name 4:2:2 indicates that there are four luminance samples and two chrominance samples for every six pixels in the image. This reduces the amount of data required to represent the image while still maintaining high quality.
4:2:0 Chroma Subsampling
4:2:0 chroma subsampling is the most commonly used type of chroma subsampling in video encoding. It reduces the spatial resolution of the chrominance information by a factor of two in both the horizontal and vertical dimensions. This means that for every four luminance samples, there is only one chrominance sample. The name 4:2:0 indicates that there are four luminance samples and two chrominance samples for every eight pixels in the image. This reduces the amount of data required to represent the image even further, but it can result in visible color artifacts in some cases.
4:1:1 Chroma Subsampling
In 4:1:1 chroma subsampling, the chrominance information is sampled at one-quarter the rate of the luminance information. This means that for every four luminance samples, there is only one chrominance sample. The name 4:1:1 indicates that there are four luminance samples and one chrominance sample for every five pixels in the image. This reduces the amount of data required to represent the image even further than 4:2:0, but it can result in more visible color artifacts.
In video streaming applications, the choice of chroma subsampling is often a trade-off between image quality and data size. Higher-quality images require more data, which can be challenging to transmit over limited bandwidth networks. On the other hand, lower-quality images with fewer data can result in visible color artifacts, which can negatively impact the viewer experience.