Up-conversion

Basic Method

The most basic method of up-conversion is to run through each line and duplicate each pixel to generate an image that is twice as wide. Applying the same process to each column of the wide image produces a final image that is double the size of the original. Whilst this is quick and simple the final image will have aliases at harmonics of the original sampling frequency. This pixel duplication method is equivalent to creating a new image by inserting zeros in-between the old pixels and filtering with a (1, 1) filter.

A much better result can be obtained by using a filter with more taps that is designed to suppress the alias components in the image. There are many different ways to design a filter and all have different tradeoffs between pass band ripple, roll-off speed etc. Optimal filter design was not the main objective of this work and will only be discussed briefly.