Editing MPEG-1 (section)

===Color space===
[[File:Yuvformats420sampling.svg|thumb|right|Example of 4:2:0 subsampling. The two overlapping center circles represent chroma blue and chroma red (color) pixels, while the 4 outside circles represent the luma (brightness).]]

Before encoding video to MPEG-1, the color-space is transformed to [[Y′CbCr]] (Y′=Luma, Cb=Chroma Blue, Cr=Chroma Red). [[Luma (video)|Luma]] (brightness, resolution) is stored separately from [[Chrominance|chroma]] (color, hue, phase) and even further separated into red and blue components.

The chroma is also subsampled to [[4:2:0]], meaning it is reduced to half resolution vertically and half resolution horizontally, i.e., to just one quarter the number of samples used for the luma component of the video.<ref name=mpeg_faqs1/> This use of higher resolution for some color components is similar in concept to the [[Bayer filter|Bayer pattern filter]] that is commonly used for the image capturing sensor in digital color cameras. Because the human eye is much more sensitive to small changes in brightness (the Y component) than in color (the Cr and Cb components), [[chroma subsampling]] is a very effective way to reduce the amount of video data that needs to be compressed. However, on videos with fine detail (high [[Spatial frequency#Visual perception|spatial complexity]]) this can manifest as chroma [[aliasing]] artifacts. Compared to other digital [[compression artifact]]s, this issue seems to very rarely be a source of annoyance. Because of the subsampling, Y′CbCr 4:2:0 video is ordinarily stored using even dimensions ([[divisible]] by 2 horizontally and vertically).

Y′CbCr color is often informally called [[YUV]] to simplify the notation, although that term more properly applies to a somewhat different color format. Similarly, the terms [[luminance]] and [[chrominance]] are often used instead of the (more accurate) terms luma and chroma.