File:125-Fold Time-Lapsed Perijove-04 Fly-Over Animation Derived from Raw JunoCam Images, 2017-02-02.webm

English: On February 2, 2017, NASA's Juno spacecraft performed her 4th perijove pass (PJ-04), a close flyby over Jupiter. Juno orbits around Jupiter take about 53.5 days. They are elliptical and very eccentrical. The JunoCam instrument, Juno's public outreach and education camera, was operational during PJ04, and took several images.

The images covered all of Jupiter latitudes. This allows rendering seamless animations from above Jupiter's north pole till above its south pole along Juno's trajectory. The animation shown here is time-lapsed by a factor of 125. Each frame of the animaton is rendered immediately from a respective raw JunoCam image. These raw JunoCam images consist of color strips ("framelets") the camera takes while the Juno spacecraft rotates with a spin rate of about two revolutions per minute. For each frame of the animation, the raw JunoCam framelets are merged to a color image showing Jupiter from a perspective as it has been for the respective simulated trajectory position. The raw JunoCam colors underwent "decompanding" and weighting in order to reconstruct approximately "natural" colors. Since the contrast of Jupiter's cloud top is mostly pretty low, for this animation, I've decided to apply two enhancement steps. First dividing by a Lambert shading model, in order to get the colors relative to a white mate solid spheroid illuminated by the Sun. In contrast to a white mate solid, Jupiter has an atmosphere. This results in a twilight zone beyond the terminator. Therefore, the previously described method of de-Lambertianing results in a brightening effect of the twilight zone. No correction has been applied to this effect. In order to further enhance constrast, I've squared the resulting radiometric quotients. In other words, I've applied a gamma-stetch of 4.0 (applying 4th power) relative to square-root encoded colors. (Raw JunoCam data are roughly square-root encoded.) As a side-effect, this additional gamma-stretch further brightens the terminator region. Future versions might adjust for the over-enhancement of the twilight. The animation is derived from JunoCam's perijove-04 images #099 to #109. The JunoCam images have been taken from different perspective along Juno's trajectory. The same surface point of Jupiter changes appearence with perspective and time. This effect is not adjusted for in the animation. Therefore the changes from one raw JunoCam image to the next is accompanied by a change of Jupiter's appearence. The simulated real time covers 2017-02-02T12:25:00.000 to 2017-02-02T14:10:00.000. For most of the sequence, north is to the left. The projection is spherical with a vertical (latitudinal) field of view (FOV) of 45 degrees, and a horizontal (longitudinal) FOV of 115 degrees. The simulated pointing is constant except three 45 degree-jumps to the left, in order too keep Jupiter in the field of view. In parts of the animation, the respective raw JunoCam image doesn't cover the whole simulated field of view. This results e.g. in a curved upper or lower truncation of Jupiter, or in an unsharp or truncated limb zone. Rendering the stills for the animation took about two days of CPU time.

Besides the raw JunoCam images (credit: NASA / JPL / SwRI / MSSS), the processing uses ffmpeg for graphics and video file conversions, SPICE trajectories dumped with the SPICE/NAIF utility spy.exe, a decompanding table provided by MSSS and accessible via NASA's PDS, preliminary radiometric calibration weights determined by MSSS, and C++ compilers to compile home-made C++ source code into proprietary image processing software.

Credit: NASA / JPL / SwRI / MSSS / Gerald Eichstädt