I repeated the same process for the frames in the other three ‘footprints’, using whichever feature was most suitable for alignment purposes. Hoping to achieve sub-pixel precision, the measurements were made on images at a scale of 200%, then applied using a separate macro within the ImageJ software utility.

Images damaged by cosmic ray hits, missing lines or truncated sections, and other flaws riddling the Voyager dataset complicated the process massively. Repairing these issues ate up a significant percentage of the total time and work invested in the project. The screenshot of the OPUS PDS results page shows some of the damaged frames that needed extensive processing, or replacing altogether.

The Mosaicing Stage

Once I aligned all the frames within the four footprints covering the Saturn system, I assembled the 150 mosaics in order to produce the final animated sequence. For reasons both of time and accuracy, I preferred a semi-automated process, especially since the steadily increasing angular size of Saturn added yet another level of complexity.

Thus, I resolved to construct the first mosaic manually, which would be my reference for the remaining 149 mosaics in the movie. I measured the ratios of pixel distances between major features, such as the Maxwell Gap within the C-ring, the inner edges of the C-ring, the outer edges of the A-ring, and the extent between the limb on the left side, and the terminator on the right.

Having measured these key points, I used the information to manually construct mosaics for frames No.50, No.100, and No.150. Since the increase in the apparent size of Saturn is non-linear (due to the acceleration of the spacecraft toward the planet), I resorted to using ‘cubic splines’ plotted in a spreadsheet to give smoothly interpolated values for the expected pixel locations of these features in the other frames.

After the values in this spreadsheet were 'plugged-in' to Paint Shop Pro macros, each mosaic was built up in a progressive manner, first joining the two frames on one side of the planet (specifically the LEFT ANSA and LEFT LIMB footprints), then likewise for the other two frames, before joining the two separate mini-mosaics to form the completed 4-image frame.

Rinse and repeat another 149 times!

Adding Color

Once completed, the black and white movie sequence looked magnificent. However, Voyager 2 had shuttered an orange-green-ultraviolet color composite only a matter of hours prior to this ring movie. Although vastly lower in resolution, it was suitable for colorizing these 4 frame mosaics. The prospect of aligning and resizing the color frame to the black and white mosaics was a non-trivial problem. Once again, I chose to manually work on four keyframes, overlaying the color data on the B&W mosaics, then utilizing the Excel cubic splines macro to plot values for all other frames.