A sibling reply to this one tell you how to tell libpng not to bother using different filters and just always use the null filter, but this will make some input images into _huge_ files (maybe similar size to uncompressed image data) so be warned.
If you had software that you knew spat out images with specific properties you could choose the filter by reference to what you know about the images, e.g. imagine you always produce noise anyway, the null filter is fine, if you produce a horizontal gradient you want the SUB filter, if a vertical gradient, the UP filter. But you'd need to make custom PNG code not rely on a generic library.
If you had software that you knew spat out images with specific properties you could choose the filter by reference to what you know about the images, e.g. imagine you always produce noise anyway, the null filter is fine, if you produce a horizontal gradient you want the SUB filter, if a vertical gradient, the UP filter. But you'd need to make custom PNG code not rely on a generic library.