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Digital Video and HD, 2nd Edition by Charles Poynton

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12

Introduction to luma and chroma

Video systems convey image data in the form of one component that represents lightness, and two components that represent colour, disregarding lightness. This scheme exploits the reduced colour acuity of vision compared to luminance acuity: As long as lightness is conveyed with full detail, detail in the colour components can be reduced by subsampling – that is, by filtering (averaging). This chapter introduces the concepts of luma and chroma encoding; details will be presented in Luma and colour differences, on page 335.

The statement is commonly made that “the human visual system is more sensitive to luma than chroma.” That statement is incorrect. It is vision’s sensitivity to information at high spatial frequency ...

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