Selection of the maximum dynamic range of transformed data and the data precision of transform matrices according to the bit depth of input data

A method of decoding image data, comprising:

• frequency-transforming input frequency-transformed image data to generate an array of output image data by a matrix-multiplication process, according to a maximum dynamic range of the transformed data and using transform matrices having a data precision;
• and
• selecting the maximum dynamic range and/or the data precision of the transform matrices according to the bit depth of the output image data, wherein
• the selecting includes:
• setting the data precision of the transform matrices to a first offset number of bits less than the bit depth of the output image data;
• and
• setting the maximum dynamic range of the transformed data to a second offset number of bits greater than the bit depth of the output image data.

A data encoding apparatus for encoding image data, the apparatus comprising:

• a frequency transformer configured to frequency-transform input image data to generate an array of frequency-transformed input image coefficients by a matrix-multiplication process, according to a maximum dynamic range of the transformed data and using transform matrices having a data precision;
• and
• selector circuitry configured to
• select the maximum dynamic range and/or the data precision of the transform matrices according to the bit depth of the input image data;
• set the data precision of the transform matrices to a first offset number of bits less than the bit depth of the input image data;
• and
• set the maximum dynamic range of the transformed data to a second offset number of bits greater than the bit depth of the input image data.

An image data decoding apparatus comprising:

• a frequency transformed configured to frequency-transform input frequency-transformed image data to generate an array of output image data by a matrix-multiplication process, according to a maximum dynamic range of the transformed data and using transform matrices having a data precision;
• and
• selector circuitry configured to
• select the maximum dynamic range and/or the data precision of the transform matrices according to the bit depth of the output image data;
• set the data precision of the transform matrices to a first offset number of bits less than the bit depth of the output image data;
• and
• set the maximum dynamic range of the transformed data to a second offset number of bits greater than the bit depth of the output image data.