Color depth and chroma subsampling are probably two of the most misunderstood aspects of digital video. Trying to educate someone about them usually devolves into a simple “more is better” conclusion, without actually explaining what’s really going on.
Unless you’re Griffin Hammond, documentary filmmaker and Panasonic brand ambassador, who explains the concepts effortlessly in a way that anyone can understand.
Color in consumer digital video is typically recorded at a bit depth of 8 bits, with chroma subsampling measured at what’s called 4:2:0. This is already more information than the average camera buyer needs to worry about, but if you’re considering upping your video skills and finding ways to improve image quality that go far beyond a simple bump in resolution, understanding what these numbers mean is important.
What is 10-bit color?
Bit depth refers to the overall number of levels of red, green, or blue that a camera records. 8 bits means there are 256 levels (0 to 255) of each color, or roughly 16.8 million combinations in total. Now, 16.8 million sounds like a lot, but one common situation where you can notice the drawback of 8-bit color is in areas of light falloff from bright to dark, which may show up as disparate bands of shading rather than a smooth gradient. This effect is prevalent on YouTube where it is exacerbated by heavy compression, although many viewers may not notice it.
Bumping up to 10 bits multiplies the levels of color by four. That’s 1,024 available values each for green, red, and blue, or a whopping one billion total combinations. As Hammond explains, however, you won’t always see this extra color information: Most screens only support 8-bit color.
But 10-bit color is your ticket to producing High Dynamic Range (HDR) content. Thankfully, 10-bit displays are increasing as HDR TVs become more common. Some phones support HDR now, and even some 8-bit displays can fake it using a technique called frame rate control (FRC).
What is chroma subsampling?
Chroma subsampling is a separate beast altogether. This is often called color resolution, as compared to the spatial resolution, like 4K. As an example, 4K Ultra HD video has a spatial resolution 3,840 x 2,160 pixels — but the color of each pixel is derived from a much smaller sampling than that.
With 4:2:0 subsampling, for every two rows of four pixels, color is sampled from just two pixels in the top row and zero pixels in the bottom row. Surprisingly, this seemingly dramatic approximation has little effect on the color, as our eyes are more forgiving to chrominance (color) than luminance (light). If your camera supports 4:2:2 subsampling, this doubles the color resolution by including color from an additional two pixels on the second row — but that’s still just half the total pixels in the image.
Note that color resolution is tied to spatial resolution. A 4K video with 4:2:0 subsampling will still sample color from more pixels than a Full HD video with 4:2:2 subsampling.
What does it mean for image quality?
If moving to 10-bit 4:2:2 has little effect on what we can actually see right out of the camera, why is it important? It all comes down to postproduction.
Bit depth is especially important to colorists — those are the people responsible for a movie’s final look — as it offers more room to push the color and exposure of video. Even if your final output is still an eight-bit monitor, working in a 10-bit space will give you more control and yield a better result that will lower the likelihood of banding when viewed on the 8-bit display.
4:2:2 chroma subsampling is also helpful in the coloring process, but is particularly useful for chroma key, or green screen, compositing. Here, the extra color resolution can be the difference between a smooth mask or a jagged outline.
Many video professionals working with mirrorless or DSLR cameras will use external recorders in order to capture more color information than what the camera can process internally. This is usually in the form of either 8- or 10-bit color depth with 4:2:2 chroma subsampling.
The Lumix GH5 was one of the first cameras that offered internal 4K recording with 10-bit 4:2:2 color, which can save videographers time and money by not requiring an external recorder.
If this explanation still left you scratching your head, rest assured that these concepts are explained much more succinctly in Hammond’s video. So if you haven’t yet, go ahead and give it a watch. Or if you’re ready to step up your game, check out our list of the best video cameras.
