6. A method for encoding a digital luminance signal and two digital color difference signals having high bit-rates and composed of first words representing color picture elements into an encoded digital luminance signal and an encoded digital color difference signal having low bit-rates and composed of second words, wherein a predetermined peak-to-peak luminance amplitude is split into luminance regions that are each associated with a table of second words of said encoded color difference signal representative of predetermined variation sub-regions in the two color differences for luminances lying within one of said luminance regions, and wherein two of said first words of said two color difference signals representing a picture element are encoded into a second word that is selected from the respective table associated with the luminance region including the luminance of said picture element and that is representative of the sub-region in said luminance region including the two color differences of said picture element.
6. A method for encoding a digital luminance signal and two digital color difference signals having high bit-rates and composed of first words representing color picture elements into an encoded digital luminance signal and an encoded digital color difference signal having low bit-rates and composed of second words, wherein a predetermined peak-to-peak luminance amplitude is split into luminance regions that are each associated with a table of second words of said encoded color difference signal representative of predetermined variation sub-regions in the two color differences for luminances lying within one of said luminance regions, and wherein two of said first words of said two color difference signals representing a picture element are encoded into a second word that is selected from the respective table associated with the luminance region including the luminance of said picture element and that is representative of the sub-region in said luminance region including the two color differences of said picture element. 9. The method claimed in claim 6 wherein said second words of said two color differences represent sub-regions in a constant quantification law for said two color difference signals, and the number of bits in said second words of each table is dependent on the extent of the variation region of said two color difference signals for the associated luminance region.