QUB2PNG, Playing with Cassini VIMS cubes Options

[ugordan]

I've made some progress with the IR channel on VIMS, have managed to do partial calibration of the cubes. It's still buggy, but at least it's something. Here's a couple of rough results, all using R=5um, G=2um, B=1.26um.


In case of Saturn the green and blue channels were scaled up to match the intense thermal radiation. The cubes were flatfielded, quantum efficiency corrected and divided by solar spectrum, though I don't know if all the steps were carried out correctly. Dark current subtraction remains to be done - it's possibly the reason why the lower left Titan insets have banding in the red channel. I'm actually pretty satisfied with the way these two turned out, they are reminiscent of official VIMS surface composites, including the "blue" material.

Hopefully I'll be able to put something out to convert cubes to PNGs before long. A better solution would be a GUI but that's the tedious part for me.

[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: 589

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: