Fork of JPEGView by David Kleiner - fast and highly configurable viewer/editor for JPEG, BMP, PNG, WEBP, TGA, GIF and TIFF images with a minimal GUI. Basic on-the-fly image processing is provided - allowing adjusting typical parameters as sharpness, color balance, rotation, perspective, contrast and local under-/overexposure.
Right now the lossless JPEG transcode feature is under the "Lossless JPEG transformations" menu, but there's probably a better place for it.