QUB2PNG, Playing with Cassini VIMS cubes Options

[ugordan]

I don't have access to that paper to really know what they did. Even if that were the case, I wonder if a repeat would be straightforward as I get the impression they were looking at very specific wavelengths on the edge of a methane window and whether or not VIMS' discrete wavelengths would fit the bill. The closest channels are 166 at 2.03424 microns and 168 at 2.06757 microns.

I did try some funky ratios between spectral windows, below are some composites. The left-hand sides show R=5 microns, G=2.7 microns, B=2 microns. The right sides are all ratio composites:
R=5 microns/2 microns
G=5 microns/2.7 microns
B=2.78 microns/2.7 microns & contrast stretched.

The upper image is one of the longest IR exposures, while the lower one is more typical of distant shots so it's more noisy.


In the 5/2 ratio image the contrast between dark equatorial stuff and the rest is practically lost. Tui Regio and Hotei Arcus consistently stand out. Intriguing.

Things at Titan at small scales really start to look strange if you take a ratio of 2.7/2.78 microns. Quivira, for example, looks completely different:


Top left: normal 2 micron reflectance
Top right: 2.7/2.78 micron ratio, heavily contrast stretched
Bottom left composite: R=ratio, B=2 micron, G=( R+B )/2
Bottom right composite: Classic 5 micron (red), 2 micron (green), 1.26 micron (blue, slightly overexposed in raw data)

[remcook]

They used filters from ground-based telescopes, so a (small) range of wavelengths convolved. The paper itself doesn't give much more info than i've just given I'm afraid. Would be cool if it was possible with VIMS too, since the spatial resolution is much better and there are lots of observations.

[Bjorn Jonsson]

This is slightly off-topic but has anyone been able to download the TIFFs on the January 1, 2008 VIMS PDS data volumes? I'm getting "430 Forbidden" when using Wget and errors too when using IE or Firefox. I get the impression that something is wrong on PDS' end. I was able to download everything else.

The TIFFs are highly useful for figuring out which QUBs you want to convert to PNGs.

[ugordan]

Yeah, the TIFFs don't work for me either, it does seem like a problem with file access permissions on their end.

P.S. If you're using QUB2PNG for the conversion be warned that the way HIRES IR cubes are flatfielded is wrong in the latest version. I fixed it in the meantime, but never got around to posting it here due to apparent lack of interest. I may post an updated version some time soon.

[elakdawalla]

Rest assured, ugordan, it's not lack of interest, just lack of time. What you're doing with QUB2PNG is really awesome. Have you contacted any members of the VIMS team to tell them about it?

--Emily

[Bjorn Jonsson]

A similar situation in my case - lack of time so only very rudimentary testing so far but this will soon change.

I've been spending huge amounts of time making DEMs of Saturn's satellites but fortunately the "development phase" is finally over. Stay tuned for "Iapetus the Movie" .

[ugordan]

Emily, I'm curious - why do you think the VIMS team would want to know about this?

Anyway, here's the version that does flatfielding correctly (as far as I can tell):
 QUB2PNGv03.zip ( 45.78K ) Number of downloads: 712


P.S. Bjorn, that movie better be released soon or we'll start to get impatient now that we're know what's been cooking

[djellison]

>2 year old thread time warp.

Version 1 and 2 run great on my machine. Version 3 crashes immediately. XP64 machine. Just doing a straight qub2png filename.qub without any other details. Anything I can do to help in identifying and fixing. PLUS - did that suggestion of automatically spitting out a true color image get any traction?

[ugordan]

Hmmm, did v3 ever work for you properly? Does it crash with every *qub file? Do you get any printouts whatsoever when you run it manually in a command line box, both with and without a filename?

[djellison]

I don't think I ever tried V3 before today - so I don't know. Every QUB I had tried crashed it, including one's that worked fine in V2 and V1.

But - inexplicably - I restart my machine at lunch, and it seems to work now. Which is v good news.

That just leaves part two - the true color interpretation.

[ugordan]

Here's a standalone version of the tool for "true" color output only as they use slightly different processing pipelines. Put the two *.tab files into that calib subdirectory where qub2png.exe already resides. Usage is pretty much the same, filename and then an optional scale factor and gamma factor. Both factors default to 1.0 if unspecified. Output is a single 16 bit RGB PNG file.

 QUB2RGBv01.zip ( 89.93K ) Number of downloads: 588

Gamma corresponds to the power function mapping linear I/F data into the nonlinear sRGB colorspace. The correct value should be 2.2 for proper contrast representation, although this is rarely used with spacecraft imagery. CICLOPS seem to use around 1.33 gamma for their releases. If you leave gamma at a default setting, the contrast and saturation will be too high if your viewing/editing software assumes sRGB gamma of 2.2 (which by and large they all do by default).
For myself, I created a custom color space in Photoshop for ISS and VIMS calibrated imagery that has gamma set to 1.0 so Photoshop converts to sRGB on the fly, but you may want to skip that hassle and hence this option.

Word of warning: many of the cubes have at least some saturated visual channels, causing pink hues to be output. This is not real, but is an artifact of the saturation, quantum efficiency of the CCD at certain wavelengths and the way color is calculated. Here are two such cases, one severe and one less noticeable:

[djellison]

RESULT

http://twitpic.com/23vggd

[mhoward]

http://twitpic.com/23vggd

I love that. It gives a dizzying sense of actually being there.

[machi]

My first larger work with VIMS spectral qubes. Thank you Ugordan for your excellent program qub2png.
Animation of southern hemisphere of Saturn from distance ~1.1 mil. km - Youtube.
Further particulars in youtube' info.

[ugordan]

Nice! I do have one question, though - if that's the *southern* hemisphere, isn't Saturn rotating the wrong way round?