Lossless JPEG

[vsaase]

Hi,

in the medical community the Lossless JPEG format (SOF type 0xc3, not JPEG-LS or JPEG2000) is very popular due to the DICOM standard. It is used for graytone images, 16 bit or 12 bit most of the time.

Some links:

• https://en.wikipedia.org/wiki/Lossless_JPEG
• https://www.w3.org/Graphics/JPEG/itu-t81.pdf

Implementations of JPEG Lossless (SOF type 0xc3):

• https://github.com/malaterre/GDCM/tree/master/Utilities/gdcmjpeg
• same as https://github.com/DCMTK/dcmtk/tree/master/dcmjpeg ?
• https://github.com/rordenlab/dcm2niix/blob/master/console/jpg_0XC3.cpp
• https://github.com/cornerstonejs/cornerstoneWADOImageLoader/blob/master/codecs/jpegLossless.js

Is anyone aware of Rust implementations? Is there maybe a quick way to do it using existing code of this library? Probably the main difficulty would be to support 16 bit?

[vsaase]

I now implemented Lossless decoding in my fork: https://github.com/vsaase/jpeg-decoder/tree/lossless

This is at the moment however a breaking change, as the decode function returns u16 instead of u8 and also internally data is now u16. We could use generics to support both.

[fintelia]

Other image-rs crates use &[u8] slices to store pixel data, even when the pixels themselves are u16's or f32's. Think that could work here?

[vsaase]

Ok, I changed it so that for 16bit images decode now returns big endian u8 bytes, like the png crate.

[fintelia]

If possible, native endian would be preferable to big endian. In the main image crate we actually end up having to swap the byte order for PNG's

[vsaase]

I also prefer native endian, changed it. I don't see the JPEG standard making a statement to that.

[Shnatsel]

Lossless JPEG has been implemented in #193; I believe this issue can be closed.