Yeah, that's the thing that always strikes me as amazing about the Pioneer Jupiter images, and why it's so important to keep them "alive." Thanks for the great versions, Ricardo.

Emily

Is it really smaller though? I didn't make measurements, but it seems to take up the same amount of latitude judging by the bands. As for the longitude, it certainly looks narrower, but much of that seems to be due to a color change; if you compare the Spot to an eye, the "eyeball" has changed from red to white, so that what seems to be the whole Red Spot is just the internal oval cyclone.

Its longitudinal extent is getting shorter - this apparent difference is real. If it continues shrinking at the same rate it will become circular around 2040 or so. That's thought to be an unstable configuration so something interesting is going to happen. The big question is - exactly what? There was also some interesting GRS discussion in this thread.

BTW I wish the original digital Pioneer imaging data were available somewhere. Due to the nature of the Pioneer imaging system (spin scan imaging with just a single 'pixel') processing the data is difficult. Still I'm sure that reprocessing it on modern computers would result in something better than the processing done more than 30 years ago. What some of the people here have been doing with ancient data like Mariner 6 and 7 images and Voyager images certainly makes this likely.

An obvious processing idea would be to simply place the spin scan pixels on a cylindrical map, project the map on an ellipsoid and render a perspective view. This was computationally extremely expensive to do in the mid 1970s but takes only a few seconds to render on today's computers. There will be problems at the limb and terminator due to Jupiter's rotation since acquiring the images took about 30 minutes IIRC but that's not a showstopper.

Great work! I am also working with that dataset. I have put most of my time into trying to find digital data, but I am beginning to to think it futile. Also, while there is slight improvement, I have found that really good reproductions can be largely reconstructed from the best versions in print. Due to the low number of pixels/high level of enlargement and 6-bit encoding, the original graylevels can be pretty well reconstructed (although it is by no means truly photometric).

Modern processing will benefit in having a better green channel (remember that the Pionners only had a Red and a Blue color channel) and in geometrical correction.
From what I've made out of the imaging system, the images were scanned using the spacecraft spin (spin scan) and movement relative to the planet. So let's say, the X axis was given by the spacecraft "horizontal" movement as it passed by Jupiter, and the Y axis by it's own rotation.
So the distortions are enormous and the images tool a lot of time to be built. We are talking several minutes here. Yet there are some good quality images taken at interesting angles. Closest approach pictures do reveal nice details, and yes, the GRS photos are unique.

I've made some progress in producing a cylindrical map out of the dataset, but it's somewhat inaccurate. So it is possible to "complete" each individual image coverage with those taken before and after.

One problem is that if you look at the Jupiter images before they were rectified, they look like sausages, thanks to the motion of the spacecraft. Also, while Jupiter was nearby, and hence large, a scan took about 40 minutes. Given the planet's fast rotation, that means a significant shift. The rectification process, while it made it look the correct shape, is therefore quite skewed.