In general, UIC covers more of the image codec specs with decode than with encode. This check implies that encoding with signedpixel data is a known limitation that is not fully implemented. UIC's jpeg2000 encode is minimalist in other ways too, such as thatoutput imagesare limited to a single tile. As a sample, it is intended to be a starting point for your development and not a product-ready jpeg2000 implementation. At this point we have not scoped out how much effort it would take to add this capability.
I couldfile thisasa feature request if you like. It would be helpful to knowa bit more abouthow you're hoping to use UIC,and specifically why you need signed encode support.