Signal compression and/or expansion devices

摘要

In a signal compressor, a blocking circuit (20) subjects pixel information of an original sample surface to blocking, a DCT circuit (30) transforms the blocks of input data, a quantizer (40) quantizes the DCT-treated data, a VLC circuit (60) subjects the quantized data to variable-length coding, and a measuring circuit (80) measures the code length based on the quantized data. Variable-length coded data or input sample data is selected in accordance with an output from the measuring circuit (80) so that when the variable-length code content after entropy coding is greater than the data content of unit input sample surface, the input sample data itself, instead of the variable-length coded data, may used as data to be compressed, whereby the average code content is reduced. In a signal expander (not shown), when the input bit stream includes a mixture of variable-length coded data and input sample date, the variable-length coded data is transformed into original uncompressed data, and the input sample data is used directly as uncompressed data.