What is Chroma Sampling in Digital Video

When the images are captured inside a video camera, the colors are captured by CCDs and put inside Red, Green and Blue filters. The media that are used to play these images are equipped with filters or phosphors to better interpret and represent these colors on screen.

Digital video is stored, and then manipulated into different chroma and luma components. This is so that the reduction of the resolution of the chroma can be done to match the resolution of the luma to cut down on the amount of data that needs to be transmitted. This compression procedure is done in a perceptually way that can’t be seen by the human eye.

There are actually many different methods to chroma sampling. The numbers that represent it is relative to the chroma resolution (last two numbers) as compared to the luma resolution (the first number). An example of this is the 4:4:4 chroma sampling. In the number 4:4:4, the first 4 is the luma resolution while the other two 4s are the Cb and Cr of chroma sampling.

Methods of Chroma Sampling

4:4:4 Chroma Sampling—This is a full resolution of both luma and chroma; no compression has been done. The number 4 is a representation of the full resolution of luma, Cb and Cr chroma sampling. This method is most likely used for RGB images.

4:2:2 Chroma Sampling—This is a full resolution of luma and half horizontal resolution of Cb and Cr chroma components. This method is the traditional standard for broadcast.

4:1:1 Chroma Sampling—this is the full resolution of luma and a quarter reolution of Cb and Cr chroma components. NTSC DV and PAL DVCPro uses this method of chroma sampling.

4:2:0 Chroma Sampling—This represents the full resolution of luma and half of the horizontal and vertical chroma components. This is the most complex of all of the methods because it has many different variants depending on what media is using the video and if it is progressive or interlaced. This method is used by PAL DV and MPEG2.

Images of Chroma Sampling

4:4:4 Chroma Sampling
4:2:2 Chroma Sampling
4:1:1 Chroma Sampling
4:2:0 Chroma Sampling