Fitting to image by piecewise bi-cubic surface

The problem of constructing surface to fit image data is discussed. The data points of an image can be regarded being sampled from an original surface which can be approximated by piecewise quadratic polynomials. On each local region, a quadratic polynomial surface is constructed with the image data as constraint. The combination of all the quadratic polynomial surfaces forms the fitting surface which approximates the original surface with a quadratic polynomial precision. The experiments for comparing the new method with the existing ones are included.