I have added the program at position 14 after IrfanView in the lossless apps list, with remark that it supports up to JPEG 7 due to the dependence on the Windows version.
The source package contains only source code in the VB language and some library components, among them this one:
So this is responsible for the JPEG functions of the program.
It seems that the JPEG lossless transformation functions are also provided somehow by GDI+, because I couldn't find them in the VB sources.
The JPEG rotation performed by the program is indeed lossless for the appropriate image dimensions.
In case of odd dimensions, a recompression is done with copying the quality-related parameters from the source, i.e. subsampling and quantization tables.
This seems like a somewhat reasonable solution.
However, it seems they forgot to transpose the quantization tables appropriately in the process.
This is a slight glitch because the quantization tables are mostly nearly symmetrical.
This is another Filmstrip image viewer with Folder Tree (=> Show Folders).
In the View mode matching Opus' Filmstrip style, Windows 11 25H2, arithmetic (trans)coded JPEG files:
Like cPicture, the program has the full spectrum of Filmstrip options: Top, Bottom, Left, Right (=> Show settings > Viewer > Thumbnails).
Regards
Guido