Down-conversion

The down-conversion routines were written after the up-conversion code had been finalised so they are quite similar. The down-conversion routine halves the size of the image and can be applied repeated times to achieve a quarter or eighth image size.

Down-converting an image that was produced by the up-conversion can be done quite easily. Simply take every other pixel in both dimensions to retrieve the original image. Applying this technique to real images that have not been up-converted does not work well and the resulting image suffers from aliasing effects.

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