Lepton support

[SergeiVorobyov]

Lepton Image Format Support

• Added support for the Dropbox Lepton image format for files with the .lep extension.
• Unlike the changes in PR #178, this implementation uses the library from the lepton_jpeg_rust project to decode Lepton files directly into memory, which are then passed to the internal JPEG encoder. This approach significantly reduces encoding time and avoids using temporary files during intermediate steps.

Given that the lepton_jpeg_rust project is well-maintained and actively developed, the encoding quality and performance are excellent. Decoding overhead is minimal, thanks to the AVX2-optimized version of the library, which JPEGView automatically selects if the processor supports the AVX2 instruction set; otherwise, it falls back to the generic version.

Note on Dependency

JPEGView does not statically link to the lepton_jpeg_rust libraries. Instead, it loads one of them dynamically when the first Lepton image is opened. By default, the following library names are used:

• lepton_jpeg.dll – for generic CPUs
• lepton_jpeg_avx2.dll – for AVX2-capable processors

These names are configurable via the LeptonLibName key in JPEGView’s INI file and can be modified if needed.