-1, I think you have a colorspace conversion error in those samples.
Black level is at 16 should be 0
White level is at 235 should be 255
Sometimes it gets this way depending on the program used to create the jpgs.
yeah, this is a simple export from avidemux,
i didn't mess around with the colors or options originally.
one quick of changing the black levels blew out the whites.
feel free to correct, and post results.
No real need to correct the contrast is pretty good as it is, but perhaps in other samples it could be more noticeable.
I usually export from virtualdubmod, if it accepts the video file that is, and it won't do jpgs.