Coding apparatus

A coding apparatus for reducing a digital image signal, comprising:

• block formatting means for dividing said digital image signal into blocks of plurality of picture elements;
• orthogonal transforming means for performing orthogonal transform on the formatted image signal;
• weighting means for performing weighting on coefficients obtained through the orthogonal transform with a weighting factor;
• means for dividing each block of the image signal outputted from said block formatting means into a plurality of sub-blocks and obtaining criterion values from the absolute value sum of difference of image signal level between adjacent picture elements in said each sub-block;
• and
• deciding means for deciding the weighting factor on the basis of said criterion values.

A coding apparatus for reducing a digital image signal, comprising:

• block formatting means for dividing said digital image signal into blocks of plurality of picture elements;
• orthogonal transforming means for performing orthogonal transform on the formatted image signal;
• quantizing means for quantizing coefficients obtained through the orthogonal transform with a quantization table;
• means for dividing each block of the image signal outputted from said block formatting means into a plurality of sub-blocks and obtaining the maximum and minimum values of the image signal level of picture elements in said each sub-block;
• and
• deciding means for deciding the quantization table on the basis of said maximum and minimum values.

A coding apparatus for reducing a digital image signal, comprising:

• block formatting means for dividing said digital image signal into blocks of plurality of picture elements;
• orthogonal transforming means for performing orthogonal transform on the formatted image signal;
• weighting means for performing weighting on coefficients obtained through the orthogonal transform with a weighting factor;
• means for dividing each block of the image signal outputted from said block formatting means into a plurality of sub-blocks and obtaining the maximum and minimum values of the image signal in said each sub-block;
• and
• deciding means for deciding the weighting factor on the basis of said maximum and minimum values.

A coding apparatus for reducing a digital image signal, comprising:

• block formatting means for dividing said digital image signal into blocks of plurality of picture elements;
• orthogonal transforming means for performing orthogonal transform on each formatted block;
• weighting means, provided with a smaller number of multipliers than the number of picture elements in said each block, for performing weighting on coefficients obtained through the orthogonal transform;
• and
• means for performing variable length coding on said coefficients on which weighting is performed.