Analysis of Linear Interpolation Schemes for Bi-Level Image Applications

In the ofice. it is often ecessary to scan a picture at a certain resolution and then reproduce it at a different (usually higher) resolution. This conversion can be achieved by interpolating the scanned signal between the sample intervals. This paper discusses a class of linear interpolating methods based on resampling polynomial functions. In addition, we introduce new methods to compare the performance of these interpolating schemes. The signal models used are one-dimensional step and pulse functions. These bi-level models are suficient to describe many blacklwhite documents. The performance of the linear interpolators is determined by evaluating their accuracy in reconstructing the original bi-level signal. The analysis considers the effects of the coarse scan and fine print intervals as well as the quantization effects. Experiments using the IEEE facsimile chart as input verifv the analytical findings. The results how the advantage of using odd-order polynomials, such as the first order and T R W cubic. Also, we discuss the relationship between the interpolating ratio and the number of quantization levels needed to represent the scanned signal.