[X] My Assistant

[Bjorn Jonsson]

This may be a bit specialized to say the least but if anyone can help I'd be grateful. I have now downloaded most of the raw Cassini images from the PDS imaging node plus the coiss_0011 volume from the PDS rings node. Volume coiss_0011 contains calibration stuff like flatfields, masks for removing dust rings and mottling etc.

I have been implementing calibration code which will eventually be added to my IMG2PNG utility, assuming there is interest in this. This utility is mentioned in this thread: http://www.unmannedspaceflight.com/index.p...wtopic=291&st=0 .

My code has been largely based on the CISSCAL source code on volume coiss_0011 but cleaned up a bit and rewritten using C++. This has been very successful despite a wide variety of rather arcane data formats on the coiss_0011 volume (bigendians, littleendians, IEEE and VAX floating point numbers, a weird TIFF file containing floating point data etc.). For example, flatfielding, linearization etc. works very well and in particular, for images of low contrast targets like Saturn and Titan makes a big difference if the images are to be greatly sharpened (no mottling or dustrings).

There is one problem though: Darkcurrent subtraction. This is a problem, the CISSCAL code for this is somewhat complex and may contain some bugs - what it does is to generate 'synthetic' darkcurrent images based on a model taking various factors into account. These 'synthetic' darkcurrent images get written to disk so each of them only has to be generated once. If anyone has 'sample' synthetic darkcurrent images I would greatly appreciate if at least one of these could be emailed to me since without this it is almost impossible for me to know if the images my code is generating are correct.

These images should (assuming my code is correct !) have names like \calib\darkcurrent\darks04228\n_dark027102410100_04228.img where '\calib' is in my case the calib-directory on the coiss_0011 DVD volume (which is lying on my hard disk).

Bjorn

[djellison]

The ISIS developers are aware that a Windows version is an almost must - HOWEVER - there's a Mac version of 2 out and about.

Doug

[Bjorn Jonsson]

The most important parts of my software for calibrating Cassini images now work and will eventually be incorporated into IMG2PNG. Making this work was greatly complicated by the fact that the Cassini calibration files are in all sorts of weird formats, TIFF files containing floating point data, PDS files containing bigendian/littleendian, VAX/IEEE floating point numbers etc. In particular, finding source code to convert VAX floats to IEEE floats took a lot of time - by 'source code' I mean something that actually works .

Using calibrated images makes a big difference for images of low-contrast targets like Titan and Saturn (no dust rings or mottling). Also most of the images have been converted from 12 to 8 bits with a non-linear function aboard the spacecraft before transmitting them to Earth.

I will upload a new version of IMG2PNG once it is complete sometime in (probably) early September. It will not work unless the entire contents of the calib directory on Cassini volume coiss_0011 are available on the machine where it is run. Beware that if you download it by getting the CALIB.TAR.GZ file and use WinZIP to decompress it you *must* turn off the TAR file smart CR/LF conversion.

BTW I have ISIS on my old machine and use it from time to time, especially when working with Voyager images (getting rid of distortion in particular) but it is not very easy to use.

IIRC the images CISSCAL outputs contain 4 byte floating point image data.