![]() Therefore it is possible to sample color information at a lower resolution while maintaining good image quality. The human vision system (HVS) processes color information, meaning hue and colorfulness, at about a third of the resolution of luminance, meaning the lightness/darkness information in an image. This reduction results in almost no visual difference as perceived by the viewer. In compressed images, for example, the 4:2:2 Y'CbCr scheme requires two-thirds the bandwidth of non-subsampled "4:4:4" R'G'B'. Since the human visual system is much more sensitive to variations in brightness than color, a video system can be optimized by devoting more bandwidth to the luma component (usually denoted Y'), than to the color difference components Cb and Cr. The lower row shows the resolution of the color information.ĭigital signals are often compressed to reduce file size and save transmission time. ![]() Note how similar the color images appear. Rationale In full size, this image shows the difference between four subsampling schemes. It is used in many video and still image encoding schemes – both analog and digital – including in JPEG encoding. Practice of encoding images Widely used chroma subsampling formatsĬhroma subsampling is the practice of encoding images by implementing less resolution for chroma information than for luma information, taking advantage of the human visual system's lower acuity for color differences than for luminance.
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