Fast inverse integer transform for video decoding

Apparatus for computing an inverse integer transform from a matrix of coefficients derived by decoding a signal, said apparatus comprising:

• a decoder that determines said matrix of coefficients, an ordered progression of indexed locations in said matrix, and an index value corresponding to a highest-indexed location in said matrix that contains a predefined coefficient;
• and
• control circuitry that:
• when said index value is in a first range of values, above an upper threshold, computes said inverse integer transform using a first group of operations;
• when said index value is in a second range of values, between a lower threshold and said upper threshold, computes said inverse integer transform using a second group of operations, said second group of operations being less complex than said first group of operations;
• and
• when said index value is in a third range of values below said lower threshold, computes said inverse integer transform using a third group of operations, said third group of operations being less complex than said second group of operations.

Video apparatus comprising:

• a display;
• and
• driver circuitry that drives said display, said driver circuitry computing an inverse integer transform from a matrix of coefficients derived by decoding of a video signal, said driver circuitry comprising:
• a decoder that determines said matrix of coefficients, an ordered progression of indexed locations in said matrix, and an index value corresponding to a highest-indexed location in said matrix that contains a predefined coefficient;
• and
• control circuitry that:
• when said index value is in a first range of values, above an upper threshold, computes said inverse integer transform using a first group of operations;
• when said index value is in a second range of values, between a lower threshold and said upper threshold, computes said inverse integer transform using a second group of operations, said second group of operations being less complex than said first group of operations;
• and
• when said index value is in a third range of values below said lower threshold, computes said inverse integer transform using a third group of operations, said third group of operations being less complex than said second group of operations.