So what type of image processing did NASA do in the early days?
- They converted the data from 8-bit (256 grays) to 6-bit (64 grays), with the notion that 64 is twice the amount humans can discern anyway.
- Apply a high-pass filter to the image: average the surrounding 125 pixels and then subtracting the running average from the value of the pixel.
- Eliminate distortion using reference points marked on the image.
- Removal of “spike noise”, by averaging – any pixel with a difference of more than 32 levels of gray from its neighbours.
Here’s an image from Mariner 4:
Here’s the associated histogram:
This process relied on the analog video signals sent back from a spacecraft being transformed into digital data, which was achieved in 1963. By 1964, the NASA Jet Propulsion Lab’s IBM 7094 system had been programmed to process Ranger data. By 1969, image processing was fully incorporated into the data processing pipeline.