Two-dimensional orthogonal digital filters (Q1299521)

The paper investigates 2-D digital orthogonal filters. The authors show that using a 2-D all-pass transformation of a 1-D digital filter realized with an orthogonal structure, one can obtain a 2-D orthogonal digital filter. The transfer function of a unit realizing the all-pass transformation can also be implemented as an orthogonal unit. The authors propose two different structures having their transfer functions of the all-pass type. Such structures can be used as replacements of delay units in a 1-D prototype to obtain 2-D filters. Two examples of designing 2-D digital low-pass filters are examined. The first example shows the use of the true rotation of the coordinate system in the complex frequency plane, while the second example uses a pseudo-rotation. In both examples, suitable 2-D frequency responses (amplitue responses) of the filters are illustrated with 3-D plots.