Exquisite Saturn Images Options

[Bjorn Jonsson]

Yes, it's probably Iapetus' shadow. In particular, there was no big storm at that latitude in September 2004. I used images obtained back then for a global map of Saturn's southern hemisphere and the longitudinal coverage is complete.

This leaves one question: The shadows in the northern hemisphere. The lower one is probably cast by Mimas but I'm not sure about the other one.

[Ken90000]

I don't know. I have been playing around with the Solar System Simulator. The only two of the "Classical Nine” satellites of Saturn able to project their shadows on Saturn’s cloudtops are Mimas and Enceladus (oh and the much misaligned Iapatus). My playing around suggests that Mimas is perfectly place to project the northnernmost (and smaller) shadow. I know there are other more accurate (and less pretty) simulators out there the include the Voyager 15 set of satellites. Sadly, I am on dial-up here in SW Indiana and have no bandwidth to search those simulators.

My vote still is an Iapetus Shadow in the Southern Hemisphere with Mimas’ shadow, although smaller, projected farther in the Northern hemisphere with one of the “co-orbitals” projecting its larger shadow closer to the rings’ shadow.

We are in for a great eclipse season. I cannot wait to see the result of Titan’s shadow on the cloudtops of Saturn.

-Ken

[stevesliva]

I still support my theory that it is the result of a partial eclipse of the sun by Iapetus as viewed from Saturn's cloudtops.

Neat... made me wonder if there were other photos of that. Like this one. Or this.

[nprev]

Stunning examples, Steve. Unfortunately, I doubt that Cassini has obtained time-sequenced imagery of satellite shadows thus far analogous to these excellent Earth/Moon series...based on what I've seen of the raw data, the spacecraft snaps maybe ten frames at the most of a given target relatively quickly, then moves on to the next objective. You're right, though--neat thought!

[volcanopele]

Yep, tis an annular eclipse by Iapetus:

[Bjorn Jonsson]

I just discovered that the smaller 'shadow' in the northern hemisphere is actually not a shadow. It is an image blemish and not a real feature. It was present in all of the source images (R/G/B) and (more importantly) it is also visible in other images at exactly the same location. The other dark spot in the northern hemisphere seems to be a real feature (a satellite shadow).

I will be posting an updated version of the color composite several hours from now.

[elakdawalla]

Here's my version of the narrow-angle image of Rhea (taken twice in clear filters plus RED, GRN, and BL1) that accompanied the wide-angle version Bjorn is putting together. To make this, enlarged all by a factor of two, aligned the red, green, and blue ones, and made the RGB version. Then I stacked the two clear ones to soften the JPEGging and futzed with the contrast a bit. Then I converted the RGB to Lab color and swapped the clear image in to the Brightness channel.


By the way, I noticed something while digging in to the Atlas images in the PDS. Whenever they take a multi-filter set on a target, most of the color filter ones are highly compressed. They take clear ones at the beginning and/or end of the multispectral sequence, and at least one of those clear-filter images is usually not compressed to nearly as high a degree. So it's probably a good practice, when making RGB composites, to overlay the RGB image on the clear-filter one to improve the detail in Cassini images.

Looking forward to your updated version of the wide-angle shot, Bjorn.

--Emily

[Bjorn Jonsson]

Here is an updated version of the WA shot:



In addition to removing the blemish in the northern hemisphere (the one I initially thought was a shadow) I aligned the color channels a bit more carefully, removed a few less obvious blemishes, made some minor resampling artifacts less obvious and made a higher quality JPG file.

The resampling artifacts were due to the fact that as usual I did most of the processing at three times the original image size and finally cropped the image a bit and shrunk it back by a factor of three.

I had already noticed that for multiple filter sequences some of the images are usually compressed. Usually not enough to be highly obvious unless you sharpen them but still enough to probably make it a good idea to use the clear filter one for the brightness channel unless the filtered images look significantly different from clear filter ones (for example MT and UV images of Saturn).

[David]

Here's my version of the narrow-angle image of Rhea (taken twice in clear filters plus RED, GRN, and BL1) that accompanied the wide-angle version Bjorn is putting together. To make this, enlarged all by a factor of two, aligned the red, green, and blue ones, and made the RGB version. Then I stacked the two clear ones to soften the JPEGging and futzed with the contrast a bit. Then I converted the RGB to Lab color and swapped the clear image in to the Brightness channel.

That's gorgeous. I love those pictures of "world against world"; they give a sense of presence, of immediacy, and of three-dimensionality that you don't get from seeing disks and crescents silhouetted against space.

I wonder if I could have permission to use that image, or a cropped version of it, as an avatar picture, since I still haven't got one? "No" is a perfectly acceptable and inoffensive answer...

[elakdawalla]

I've now blogged my and Bjorn's images. While doing that, I decided it was time to write something I'd meant to do a long time ago:

A tutorial on making RGB images with Photoshop

I would really love people to test out the tutorial and send me comments.

Thanks!

Emily

[tedstryk]

WOW! This thread has been a nice welcome-home present!

[ElkGroveDan]

Emily that was a great tutorial, concise yet clearly detailed. The only thing I do different is that I align the off-set images using transparency adjustments - more than anything because the difference blending tool wasn't available on the earliest versions of PS that I taught myself on.

I'm going to bookmark this. It's much better than the one on the MER web site. Which makes me think you should also write one up for your readers on the anaglyph process too.

[Ian R]

Emily, I hope you don't mind, but I took your image and adjusted the R/G/B levels until the colours matched Bjorn's composite:



I'd also like to congratulate you on an excellent tutorial. The only possible addition I can think of at this time is to mention the alternative to the 'Difference' layer attribute that I use. Changing the top layer opacity to 50%, as well as converting it to a negative image, is the best way to accurately align two layers(in my opinion).

Ian.

[ugordan]

Another nice Saturn shot taken on July 28:

[ugordan]

Another one from quite an extensive wide-angle sequence as it turns out. This one doesn't have a green frame unfortunately, but it does feature a rare capture of Titan and Saturn in the same frame, a whole transit sequence as a matter of fact. Dione also included.

As I said, synthetic green needed to be produced and this somewhat reduced the hue range usually seen on Saturn's disc.