Preserve "progressiveness" of JPEG files

[mandx]

Most of all JPEG files uploaded to my sites are saved in progressive format, but no thumbnail generated by sorl-thumbnail is generated as progressive when the original image is. This is essential when creating thumbnails of large images, for instance, for display within a carousel/slider.

Is there a quick way to workaround this, like a custom backend based on the existing ones?

[sorl]

Added 'progressive' option in dev branch, Thanks!