[X] My Assistant

[Nirgal]

Hi all,

motivated by the impressive raw imagery discovered by n1ckdrake and others in the PDS archives I'd like to do more work with the CTX
images ... however, when I'm download und unpack the images from the PDS archives (via img2png) and looking at the histogram then it seems that the greylevels of each image only occupy a rather limited range of about 60 DN , so could it be that the dynamic range of
the CTX camera is in fact only 6 bit, or is part of the original range lost in the course of the processing for the IMG files ? This seems strange considering the very high spatial resolution of the CTX.

Especially when looking at some of the
CTX JPG images published by MSS themselves
which all look like a considerably higher dynamic range than the streched IMG raw counterparts from PDS

Unfortunately I couldn't find much specification about the CTX image processing chain ob the web (www.msss.com)
So it is my hope that some of the experts in this forum experienced with PDS raw data could shed some light on this.

Thanks for any answers in advance.
Bernhard

[djellison]

Hopefully Mike C will be able to chip in. It's a stunning camera - great images, and hopefully, a global map in a couple of years

Doug

[mcaplinger]

Hopefully Mike C will be able to chip in.

The specification document should tell you all you need to know: the 8-bit archived data has gone though the instrument's 12-to-8-bit internal companding table, so it's not linear. There are response coefficients on the PDS volumes to clean up the pixel-to-pixel variation. I've never used the ISIS tools so I don't know anything about that processing flow, but from cartrite's example they seem to work quite well.