Bulk image convert to progressive
Progressive JPEG is a format, used on the web, that is loaded progressively. First showing a picture (whole) low quality which gradually increase quality as more data are obtained from the image of the network. Progressive JPEG improving the compression organizing better the bytes and giving special treatment to the data and noise.
This does not mean that the image quality is reduced.
In this web as an experiment about the size of the JPEG, being compressed with and without progressive.
Hope it Help.