Processing the Viking Lander camera data [pdf]

You can reproduce some of the image processing described here with software today.

For example, in Figure 3, the histogram at the top right is a "periodogram" of the original image data. It shows that the original image is skewed towards the high end of the frequency spectrum. They apply a high-pass filter (discard the lowest frequencies) so the processed image shows higher details than the original.

If you had the original photograph as an image file, let's say an image of the surface of Mars, [0] you could filter out the lowest ten frequency components with a Python script: [1]

    pip install avena
    avena filter high 10 pia19676-fig1_ml_mcam04403coloradjusted24bwscale.jpg

The result: http://imgur.com/a/ASusx

Notice the details are more visible.

[0] http://www.nasa.gov/jpl/msl/pia19676/geological-contact-zone...

[1] (shameless plug) https://github.com/eliteraspberries/avena

About two years ago the Avaneya project released software that can decode the Viking Lander tapes. A few tapes contain images that were (as far as I know) never released.

Beautiful results: https://gist.github.com/jakeogh/fa995a3277d500ab59b1

There's even a very nice DVD which takes the included raw tape data and processes it: https://directory.fsf.org/wiki/Avaneya:_Viking_Lander_Remast...