PJ49 Challenging images

To return as many images as possible, Junocam typically uses a lossy image compression algorithm, similar to JPEG, which was originally developed for the Mars Observer Camera in the late 1980s. This algorithm runs in Juno's main computer and compresses the images by factors of 5 to 20. The compressed images are then stored in a large DRAM buffer to await transmission to Earth; this buffer is protected by an error-correcting code (ECC).

Unfortunately, as Juno encounters more and more radiation, so many bits are changed that the damage is sometimes beyond the ability of the ECC to correct. This results in unrecoverable errors to the compressed Junocam data. Once decompressed, such images look much like the bad video often seen in the early days of HDTV television, where the "transform blocks" that image compression algorithms use turn into mostly-random noise in some areas of the image but not others. We held back these images from the normal processing flow to avoid confusion, but provide them separately in case anyone wants to try their hand at repair.

Going forward, we plan to use our lossless compression algorithm, which is by design more resistant to bit errors at the cost of providing much less compression (typically only about 1.5:1) and allowing fewer images to be taken.