Encoding and transmission method with at least two levels of quality of digital pictures belonging to a sequence of pictures, and corresponding devices

An encoding and transmission method with at least two levels of quality of digital pictures made of picture elements, the method comprising the steps of:

• partitioning each of said digital pictures into blocks of picture elements;
• applying a reversible mathematical transformation to each of said blocks of picture elements to form transformed blocks of transformed coefficients;
• quantizing said transformed coefficients to form quantized coefficients;
• encoding the quantized coefficients to form encoded coefficients;
• distributing said encoded coefficients into a first and at least one second digital trains of encoded coefficients, the first digital train including basic coefficients corresponding to lower spatial frequencies, and at least one second digital train including a set of complementary coefficients corresponding to higher spatial frequencies;
• channel encoding the encoded coefficients of said first digital train with a first level of protection against transmission errors to form a first series of first data elements to be broadcast;
• channel encoding the encoded coefficients of said at least one second digital train with a second level of protection against transmission errors to form at least one second series of second data elements to be broadcast, said first level of protection being greater than said second level of protection;
• providing a plurality of orthogonal frequency carriers to be simultaneously broadcast;
• distributing said plurality of orthogonal frequency carriers into a first and at least one second distinct sets of frequency carriers;
• modulating each of the frequency carriers of said first set of frequency carriers with distinct data elements picked up out of said first series of first data elements so as to time and frequency interleave all said first data elements in such a way to prevent two successive data elements of said first series of first data elements from being transmitted on a same frequency carrier of said first set of frequency carriers;
• modulating each of the frequency carriers of said at least one second set of frequency carriers with distinct data elements picked up out of said at least one second series of second data elements so as to time and frequency interleave all said second data elements in such a way to prevent two successive data elements of said second series of second data elements from being transmitted on a same frequency carrier of said second set of frequency carriers;
• simultaneously broadcasting the plurality of modulated orthogonal frequency carriers, each of said digital trains being broadcast at a fixed rate relative to each other.