PixelRepresentation in JPEG Lossless

[ruslik]

Hello,

I have a question related to the compression of signed pixel data with lossless jpeg. Offis brings the pixeldata in the unsigned range before the compression, modifies the Modality LUT, and sets the PixelRepresentation to unsigned.

My question is if it is legal to have image compressed with JPEG Lossless having signed PixelRepresentation, and how should it be decoded?

I can think of two different ways of decompression of such images:
- considering that after decompression the pixel data is already signed (that would mean that the compression rate is horrible, because small differences between signed values around 0 (as 0xffff and 0) would be seen as huge differences)
- or considering that pixeldata was brought to the unsigned range for better compression rate, so that i have to substract 0x8000 (or maybe 2^HighBit ?) to obtain the original pixel data.

Thanks,
Ruslan.