You may often hear the number 10-bit 4:2:2 or 8-bit 4:2:0 when you are choosing photographic equipment or live broadcast equipment, but do you actually know what are they? What effect does it have on the picture? In this article, we will explain to you in detail.
First, let’s have a quick look at Color Depth and Chroma Subsampling.
Color depth is also known as bit-depth which refers to the number of bits used to define the color channels, red, green or blue, for each pixel. In most RGB systems, there are 256 shades per color channel. Which is 2 raised to the 8th power or the 8-bit color depth. This means that each of the RGB channels has 256 shades so there are 256x256x256 or 16,777,216 colors in total in this 8-bit RGB system. An 8-bit color system is capable of producing over 16 million colors. This may look humungous, but when it is compared to 10 bit, this is actually nothing. In a 10-bit system, you can produce 1024 x 1024 x 1024 = 1,073,741,824 colors which is 64 times the colors of the 8-bit. As a result, increasing the color depth will enable you to better represent your colors.
Chroma Subsampling is a type of compression that reduces the color information in a signal in favor of luminance data. A video signal is split into two different aspects: luma information and color information. Luma defines most of the picture. Imagine if your image has no luma information, you will see nothing except black. In contrast, a black and white image will not look less detailed than a color picture. Color information is important as well but has less visual impact. What chroma subsampling does is reduce the amount of color information in the signal to allow more luminance data instead.
This allows you to maintain picture clarity while effectively reducing the file size up to 50% that helps a lot. Because it reduces bandwidth without significantly affecting picture quality.
What is the Difference Between 4:4:4/4:2:2/4:2:0 Chroma Subsampling?
Video is sampled and transmitted in the form of three components: Y, Cb, and Cr, where Y is the Luma (brightness information), Cb is the blue difference channel (color information), and Cr is the red difference channel (color information). Each type of subsampling is represented by three numbers, indicating how much of the sampled data passes to a small group of pixels consisting of two lines with four pixels each. The first number describes how many pixels on each line get a unique brightness level. The second number describes how many pixels on the upper line get unique color information. The third number describes how many pixels on the lower line get unique color information. A signal with chroma 4:4:4 transports both luminance and color data entirely. 4:2:2 has half the chroma of 4:4:4, and 4:2:0 has a quarter of the color information available.
When contributing live broadcast content over the internet, 8-bit color pixel depth and 4:2:0 is often sufficient. However, 10-bit videos provide more color information to produce higher quality content. A 10-bit video is extremely useful for correcting colors on the fly. With 10-bit video, colorists are given more options and more control over how to process video content as there is more information available for adjusting tone curves. There is no perceptible difference between 4:2:2 and 4:2:0 when viewed at a normal viewing distance. But a 4:2:0 signal saves fifty percent of the bandwidth compared with the same video at 4:2:2. So which one is right for you is depended on your needs.